Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
In this research, stepwise cooking and temperature fuzzy controller were designed during the infrared irradiation of apple with intermittent heating method. For this purpose, the dry blanching process and dehydration of apple slices were examined at three temperatures of 70, 75 and 80 °C based on ...
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In this research, stepwise cooking and temperature fuzzy controller were designed during the infrared irradiation of apple with intermittent heating method. For this purpose, the dry blanching process and dehydration of apple slices were examined at three temperatures of 70, 75 and 80 °C based on the blanching speed and vitamin C preservation. The fuzzy controller of the temperature with the feedback loop was designed, simulated, and implemented by comparing two first and second order transfer functions in MATLAB software. Simulation efficiency was examined using the indices of integral squared error (ISE), integral absolute error (IAE), integral time-weighted absolute error (ITAE) and steady state error (ess). The results revealed that the temperature of 80 °C and time of 15 minutes were appropriate for blanching operation and temperature of 70 °C was appropriate for dehydration. The simulation results confirmed that the higher order of the transfer function led into a faster response, but increase in oscillations and reduction in the stability were not appropriate. For the first-order transfer function, the values of efficiency indices, including (ISE), (IAE) and (ITAE) were calculated to be 0.760, 0.821 and 0.589, respectively, of second-order transfer function. The simulation indicated the reliability of the fuzzy control model and showed an acceptable computational efficiency, since the fuzzy rule test during simulation showed a high sensitivity to maintain steady state error (ess) close to zero.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
Introduction: Fruits and their products in the dried form are good sources of vitamins, energy and minerals. However, during the process of drying or dehydration there are changes in quality parameters in dried products. Texture is one of the most important quality attributes of fruits during drying, ...
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Introduction: Fruits and their products in the dried form are good sources of vitamins, energy and minerals. However, during the process of drying or dehydration there are changes in quality parameters in dried products. Texture is one of the most important quality attributes of fruits during drying, reflecting their mechanical and microstructural properties. Apple is perishable fruit. Drying of apple is very important because of High losses are experienced during the seasonal glut. A novel process in food industry is the simultaneous infrared dry blanching and dehydration operation (SIRDBD) with intermittent heating method (radiation at constant temperature) exerted on fruits and vegetables that is known to enhance the quality of the final product. In the food industry, end-products must achieve a compromise between several properties, including sensory, sanitary and technological properties. Prediction of changes in texture during drying could be helpful in a better process control and improvement in overall acceptability of a dried snack food. The change of the elastic or viscoelastic texture of the fresh apples to rigid, fragile and brittle in the apple chips were evaluated by instrumental and sensory methods. Many attempts have been made to describe the viscoelastic behavior of dehydrated fruits and vegetables. Maxwell’s or compression models are limited to homogeneous, isotropic materials. In contrast, texture profile analysis (TPA) is more suitable for heterogeneous biological materials and shows a good correlation with organoleptic evaluation. Typical TPA parameters are including hardness, adhesiveness, springiness, cohesiveness, gumminess, chewiness and resilience. In this research, for the first time, textural analysis of dried apple slices by infrared heating at different temperatures and different moisture levels was performed. Finally, the optimum texture and overall acceptance of the product are described according to the instrumental analysis. Materials and methods: Apples (Golden Delicious variety) were purchased from a local market and kept in 0°C±1°C and relative humidity ranging from 90% to 95%. Before every thermal processing, the apple specimens were picked up from the cold storage and then they were put into use after reaching the ambient temperature. The samples were skinned manually and then cut into slices with different thicknesses of 5mm, 9mm and 13mm, all 20mm in diameter. The sliced apples were immediately subjected to simultaneous blanching and infrared drying. The texture of dehydrated apple slices using infrared radiation at three surface temperatures of 70, 75 and 80 °C were studied. The product in three thicknesses was dried to achieve a moisture level of 15, 20 and 25% wet weight basis. Then, texture profile analysis (TPA) was carried out to 50% compression strain using texture analyzer. The sensory evaluation of dried slices was also considered for desire texture (Good mouth feels texture, lack of hard tissue, no shrinkage) and overall acceptance (The final acceptability of the product in terms of total sensory properties including color, texture, flavor and aroma) by 10 professional panelists. For statistical analysis, a completely randomized design (CRD) was used in a factorial form (33) and Duncan test with 95% confidence level. Result & Discussion: The results showed that drying to studied moisture levels reduced the hardness and adhesiveness and increased springiness, cohesiveness, gumminess, chewiness and resilience in comparison with raw apple tissue. Hardness of samples dried at higher temperature was higher due to rapid removal of moisture which might have caused collapse of capillary voids inside the product. Due to shrinkage samples became denser and thus a larger fracture force was to be expected. As water content increases (i.e., higher RH) water plasticizes the cell walls and the material and product becomes softer and more pliable, thus hardness decreases. The increase of hardness could be because the rapid mass transfer that damaged the membrane and cell structure of the fruits during drying. Another important factor responsible for the increase of hardness of finish-dried samples is the low final moisture content when compared with other samples. High temperature drying method enables samples to reach low moisture content at relatively short duration and therefore the product with harder texture was obtained. The maximum value of adhesiveness was observed for fresh apples, which could be attributed to the high moisture and sugar content. Adhesiveness decreased with moisture loss, indicating the availability of free water on the sample surface. A significant decrease in springiness following high-temperature drying could be attributed to the glass transition phenomenon and changes from elastic to plastic behavior. In the period of softening, cohesiveness increased with moisture loss. Hardening caused a decrease in cohesiveness depending on the drying temperature. Gumminess is the energy required to disintegrate a semisolid food to a state of readiness for swallowing. High values of gumminess revealed “firm” and “crisp” with a cell rupture mode of tissue failure and lowest values of gumminess could be classified as “soft”. At the end of drying and with apple hardening, chewiness increased to values equal or above initial chewiness, indicating that a larger amount of energy is needed to masticate dried apples. Resilience had increasing with moisture loss. By increasing the thickness of the slices, the cohesiveness and springiness decreased and hence chewiness significantly decreased. The overall acceptance and desire texture in dried samples was observed at lower water evaporation rate conditions (lower temperatures, lower thickness and higher moisture content). In these conditions, the hardness of apple slices tissue was equal to 695.177 ± 7.685 grams. During drying of the apple, textural behavior was varied from the viscoelastic (higher initial hardness, with cohesiveness, springiness and lower resilience) to elastic and then to plastic or glassy.
Sara Aghajanzadeh Suraki; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad; Abas Rezaei Asl
Abstract
Introduction: Tomato consumption is recommended due to its brilliant color, amazing taste, high antioxidants and vitamins content. Pectin methylesterase (PME) is known as a pasteurization index in tomato juice. This enzyme plays important roles in cloud stability, color, viscosity and organoleptic properties ...
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Introduction: Tomato consumption is recommended due to its brilliant color, amazing taste, high antioxidants and vitamins content. Pectin methylesterase (PME) is known as a pasteurization index in tomato juice. This enzyme plays important roles in cloud stability, color, viscosity and organoleptic properties of the juice. PME induces the cloud loss in the juice due to the formation of the insoluble calcium pectate; its inactivation is therefore needed to maintain the juice stability. Degradation of ascorbic acid (AA) in the juice is considered as a major challenge during thermal food processing procedures. Furthermore, during its degradation non enzymatic browning occurs, affecting the taste and color. Novel juice processing methods such as infrared (IR) heating and pulsed electric field (PEF) reduce the adverse effects of the conventional thermal method. Quick IR heating produces a juice having higher nutritional value and better quality. During PEF processing, the juice is subjected to high voltage electric pulses for a few microseconds to inactivate target microorganisms and enzymes. Considering the protein structure of the PME, PEF processing at a higher temperature can be effective in this enzyme inactivation. A quick pre-heating of the juice using IR heating was therefore applied in this study. Furthermore, the ohmic heating, occurring during PEF treatment, was not prevented. The synergistic effect of thermal treatment and a non-thermal one (continuous PEF system) on some physicochemical properties of tomato juice were investigated.
Materials and methods: Tomato juice, with an initial temperature of 30℃, was firstly preheated using a continuous IR heating system. During the IR treatment, a temperature controller was applied to set the outlet temperature of the juice to 40, 45 and 50℃. The preheated juice was then passed through a continuous PEF system. The process chamber of the PEF system consists of two parallel stainless steel electrodes with 0.55 mm distance. The length and width of the exposed electrode surface were 10 mm and 0.5 mm, respectively. A square-wave bipolar pulse with a width of 1 ms was selected to perform the treatment within the range of 22.73 to 36.36 kV/cm at 32 Hz. The outlet temperature of the juice was recorded using a data acquisition system during 3.52 s PEF treatment. The treated juice was cooled in an ice-water bath to minimize the effect of cooling period on PME inactivation. AA content, PME activity, cloud value and color of the juice were measured using iodine titration, Kimball, spectroscopy and image processing, respectively.
Results and discussion: Results showed that higher PME inactivation was observed in the juices treated at higher IR pre-heating temperature in combination to higher PEF intensity, resulting in higher cloud stability of the juice. While preheating of the juice decreased the AA content, PEF treatment has no significant effect reflecting the heat sensitivity of this vitamin. Furthermore, color aspects of the juice were more affected by heating treatment in comparison to the PEF processing. Browning index (BI) increased as the AA content decreased. By measuring the total color difference (TCD) it was shown that the PEF had no impact on color properties of the juice. Therefore, the synergistic effect between the IR heating and PEF treatment was also effective in producing the juice having the high nutritional value and better appearance.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
Introduction: L-Ascorbic acid (vitamin C) is the most important vitamin in terms of nutrition. Ascorbic acid is a thermolabile (heat-sensitive) compound that can be degenerated aerobically or anaerobically. The degradation rates of ascorbic acid differ with the changes in environmental conditions such ...
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Introduction: L-Ascorbic acid (vitamin C) is the most important vitamin in terms of nutrition. Ascorbic acid is a thermolabile (heat-sensitive) compound that can be degenerated aerobically or anaerobically. The degradation rates of ascorbic acid differ with the changes in environmental conditions such as temperature and water activity. It is ascertained that the other nutrients residing in a food can be preserved in case the Vitamin C content is preserved. Thus, the compound is considered as the nutritional quality index during the food processing. The simultaneous infrared dry-blanching and dehydration (SIRDBD) with intermittent heating method is a novel process in which the temperature is kept constant. Over-blanching causes product quality decline and nutrients, especially vitamins, deterioration. Therefore, the precise process conditions (time and temperature) are specified with the objective of preventing over-processing. To do so, such factors as access to the specific center temperature, access to a certain level of enzymatic inactivation and preservation of a given ratio of Vitamin C should be taken into account. This is subject to the biophysical properties of fruits and slices size and shape. The aim of this study was to determine the appropriate operating conditions for blanching step. For this purpose, the effect of irradiation temperature and thickness of the product on the destruction of polyphenol oxidase (enzymatic browning agent) and vitamin C were investigated.
Materials and methods: Apple slices (Golden Delicious variety) were prepared with thickness of 5, 9 and 13 mm and 20 mm in diameter. Irradiation was carried out at three constant temperatures of 70, 75, and 80 ° C. The central temperature of the product was recorded during processing. To evaluate the enzymatic activity of polyphenol oxidase (PPO) and its effect on the product color, apple slices were removed from the device in 2- minute intervals and the process was continued till the time no sign of color change stemming from catechol reagent addition was observable. Vitamin C content measurement was carried out with 30- minute intervals during drying till apple slice reaches constant weight. It was performed based on titration by the use of 2, 6-Dichlorophenol-Indophenol (DCPIP). To calculate the browning index (BI) due to PPO activity, image acquisition was made with the use of a flatbed scanner. The treated samples were placed on the scanner and then a black box was utilized so as to prevent the interferences of the peripheral lights and light reflections. The images featured a 300 dpi quality and were saved in TIFF-24 bit format. Color analysis of the obtained images was carried out in color spaces L*a*b* by the use of “color space convertor” pelagin in ImageJ software, version 1.6.0. Statistical analyses were carried out in SPSS software, version 19. To do so and in order to assess the time required time for the blanching, there was made use of completely randomized design (CRD) in factorial format (32) considering two factors, namely thickness (in three levels) and temperature (in three levels). The statistical analyses of the vitamin degradation kinetic constant (k), as well, were conducted based on randomized complete block design (RCBD) in the course of which the temperature and thickness were considered as the block and the treatment, respectively. Mean comparisons were undertaken based on Duncan test in a 95% confidence level (P
Mina Davoodi; Mahdi Kashani-Nejad; Aman Mohammad Ziaiifar; Mohammad Ghorbani
Abstract
Introduction: There are many methods for freezing and thawing of meat. Suitable technology must be applied for freezing and thawing of chicken to keep the quality of product effectively. Novel methods including high pressure, ohmic heating and high-voltage electrostatic field have been recently considered ...
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Introduction: There are many methods for freezing and thawing of meat. Suitable technology must be applied for freezing and thawing of chicken to keep the quality of product effectively. Novel methods including high pressure, ohmic heating and high-voltage electrostatic field have been recently considered for thawing process. IR heating provides positive advantages compared to conventional heating such as reduced quality losses, shorten heating time, significant energy saving and uniform heating. Although IR has been used for various food treatments but a few researches have been reported for its application in thawing process. This study investigates the effects of this new method on thawing time, thawing loss, thawing rate, water holding capacity, color, pH, shear force, characteristics of frozen ground chicken and also optimizes the thawing conditions using response surface method.Material and methods: Fresh chicken breast was purchased from a local market (Gorgan, Iran). After washing and mincing, they were cut into a cube form (3×3×5 cm3) and stored in the freezer at -20 ℃ for 5 days before thawing process. Thawing was performed using an IR-warm air apparatus consisted of IR lamp (Far IR 1500 watts), heating elements (4 electrical elements with power 750 W), air velocity unit, centrifugal fan and thawing chamber. For thawing of samples, three variables including IR power (12.27- 247.73 W), air temperature (27.57- 49.43℃) and air velocity (0.21- 7.47 m/s) were applied. The central composite rotatable design was created by entering the three independent variables at five different levels in 20 runs with six central points. Response surface analysis was performed using Design-Expert software. The equipment was allowed to work at least 10 min to stabilize the specified conditions before the start of each thawing run. Frozen sample was then removed from freezer and placed under the infrared lamp with 12 cm distance. Quality of ground chicken breast was determined by thawing time, thawing loss, thawing rate, water holding capacity, pH and color indices.Results and Discussion: The methodology and techniques used in freezing and thawing processes play an important role in the preservation the quality of frozen foods. The results showed that increasing IR power, air temperature and air velocity decreased the thawing time (13.5–6.8 min), thawing loss (6.1–0.03 %) and increased thawing rate (11.11-30.67 cm/h), WHC (65.45–94.16 %) and improved the quality characteristics of thawed ground chicken. Generally, the ability of meat to retain free or bound water is one of the important quality characteristic of raw meat. One of the most important indicators of quality on thawing food is water holding capacity. The final pH is dependent on the amount of drip loss between the stocky and tenuous filaments. In addition, the difference in pH can be due to texture damage. Generally, the pH of chicken breast after postmortem is about 5.6- 5.8. The ∆E values and pH of the ground chicken breast was also in the same range during thawing process. Numerical optimization conditions were investigated based on the lowest thawing time, thawing loss and highest thawing rate and water holding capacity. The best suggested condition by the software was IR power 247.73 W, air temperature 38.97℃ and air velocity 6.75 m/s (desirability= 0.79). Based on the obtained result using T-test analysis, there was no considerable difference between the experimental values and the predicted one (P
Najimeh Taghavi; Aman Mohammad Ziaiifar; Habibollah Mirzaee; Alireza Sadeghi Mahoonak; Mohammad Ghorbani; Hassan Sabbaghi
Abstract
Introduction: Frying is a unit operation in which food is heated in oil to alter its eating quality. First reviews of frying performed on the principles of heat and mass transfer and oil uptake in foods, because during the frying process heat and mass transfer occurred between product and frying medium. ...
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Introduction: Frying is a unit operation in which food is heated in oil to alter its eating quality. First reviews of frying performed on the principles of heat and mass transfer and oil uptake in foods, because during the frying process heat and mass transfer occurred between product and frying medium. In fact, the food loses moisture content and lost water will replace with oil. The moisture loss in the product causes rapid formation of the crust while the core remains soft and moist; therefore higher oil uptake occurred in the crust. There is an argument about the effect of frying on the sensory characteristics of foods, changes of nutritional value and health concerns in fried foods and methods applied to reduce oil content. Consumers prefer eating foods with lower oil content. One of the typical methods for reducing oil uptake in food commodities is using of coating before frying process. Edible coatings are known as a thin layer of edible polymers which is placed on the surface of the food. Application of edible coating decreases some destructive factors like the presence of various gases such as oxygen and carbon dioxide and humidity. Hydrocolloides are referred to a group of polysaccharides and proteins which create many features such as consistency in aqueous solutions, foams stability, emulsions, improve the sense of mouth and create a similar state of fatty and oily mode for products with lower content. In fact hydrocolloid coatings can reduce the excessive oil uptake due to their interesting thermogelling properties and at the same time they are invisible and have no negative influence on the sensory attributes of fried foodstuff. Even more, fried products have low fat content with improved nutritional values, higher crispiness and better palatability. Pishmeh is described as deep-fried dough pastry which is usually prepared by local producers of Turkmen (Iran). This product absorbed high oil content during frying process. This study was carried out to evaluate the effects of hydrocolloid coatings including Aloe Vera, Carboxymethyl cellulose (CMC) and Xanthan on the oil uptake of Pishmeh.
Materials and methods: Hydrocholloid materials such as Aloe Vera, Carboxymethyl cellulose (CMC), Xanthan and complex of Xanthan-CMC were used. The gums were prepared at concentrations of 0.5 and 1% by dissolving in water at 70 ° C by stirring with a homogeneous mixer until a clear suspension was obtained. To extract the Aloe Vera gel, first, a thick epidermis (The shell) was separated from parenchyma using cutter. The parenchyma was immersed in a container of distilled water to lose bitter taste for 5 minand then parenchyma was taken out from water and transferred into a mixer (for 1 minute at 25 °C) and finally converted to a uniform colloidal solution. In the next step, the prepared dough samples were immersed in the colloidal suspensions for 1 min and the coated samples were placed on a mesh tray to remove the excess residuary coats. The samples were fried in sunflower oil at 170 °C for 6 min. The samples were then placed on a metal tray after frying to remove excess oil. After removing the oil and reaching the ambient temperature, physical and chemical tests were carried out on the sweet Pishmeh. The experiments included determination of moisture, fat content, measurement of coating parameters (such as coating ratio and frying efficiency) and color analysis.
Results and Discussion: The result showed that coating by hydrocholloid materials was led to decrease water loss in comparison to non-coated sample (control) during frying. Furthermore, oil uptake of coated samples was lower than control sample (p
Zahra Mohammadi; Mahdi Kashani-Nejad; Aman Mohammad Ziaiifar; Mohammad Ghorbani
Abstract
Introduction: The commercial lye peeling method used in kiwifruit processing industry is water and energy intensive process and has negative impact on the environment. Infrared (IR) technology has been proposed as an alternative to food processing technologies with attractive merits such as uniform heating, ...
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Introduction: The commercial lye peeling method used in kiwifruit processing industry is water and energy intensive process and has negative impact on the environment. Infrared (IR) technology has been proposed as an alternative to food processing technologies with attractive merits such as uniform heating, high heat transfer rate, reduced processing time and energy consumption, and improved product quality and safety. However, no previous reports were found on the feasibility of kiwifruit peeling using IR heating technology. Therefore, the goal of this research was to develop a new and sustainable peeling technology for kiwifruit using IR radiation heating.
Materials and methods: A lab scale IR dry-peeling system for kiwifruit was designed and constructed. The system consisted of two major sections including the IR heating and rotating rollers. The rotating kiwifruits (Actinidia deliciosa cv Hayvard) were heated using a ceramic IR element. The effects of IR radiation power (250-850 W), distance between IR emitter and sample (10-70 mm) and heating time (45-125 s) on the peeling performance of kiwifruit were investigated. The lye peeling method including 15% NaOH solution at 95 ͦC for 4 min was selected as a control treatment. The operating parameters of IR peeling were optimized using RSM.
Results and Discussion: The second-order polynomial models predicted by RSM showed a significant fitting (p < 0.0001), and the lack of fit for all fitted models was found to be not significant (p > 0.1105). The validation experiments were in good agreement with the predicted values by the fitted models. The heating with a power of 446 W at the distance of 70 mm for 125 s were found as the optimum operating conditions for kiwifruit IR peeling. The comparison of the peeling performance of kiwifruit peeled by IR and by lye peeling showed that both the IR and lye peeling could produce a satisfactory peelability (> 90%) and ease of peeling (> 4.5) for kiwifruit. The IR peeled kiwi had significantly low weight loss (4.5% vs. 11.7%), surface temperature (64.1 ͦC vs. 95 ͦC) and color difference (2.4 vs. 11.4) and high firmness (57.5 N vs. 40 N) compared to lye peeled treatment. Because the dry-peeling is a chemical- and water- free process, residuals of kiwifruit skins after IR peeling could be easily utilized as value-added by products. Based on the research results, it is concluded that IR dry-peeling has a promising potential for commercialization. This investigation should also help kiwifruit processing industry in developing the environmentally safe IR peeling technique to produce high quality products from kiwifruit.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
Introduction: Color is the most important feature of food appearance, since it strongly affects consumer acceptance. The abnormal color is closely related to degradation of food quality or food spoilage. Various factors affecting color of the product include the composition and surface properties of ...
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Introduction: Color is the most important feature of food appearance, since it strongly affects consumer acceptance. The abnormal color is closely related to degradation of food quality or food spoilage. Various factors affecting color of the product include the composition and surface properties of the foodstuff, process conditions (temperature and time), and the type of pretreatment processes. Therefore, for the design of a new process, kinetic modeling is essential for extracting basic kinetic information in a system to predict changes. Intermittent irradiation is the novel processing method in food industry which the surface temperature of product is kept constant. Darkening process occur in the fruit slices during drying, resulting in undesirable color changes. Undesirable color variations can be attributed to Millard's browning reactions between sugar and amine compounds or ascorbic acid oxidation. Thermal degradation kinetic models define maximum maintenance conditions for qualitative factors to produce a safe food. Color descriptive models are known as zero order, first order, and fractional conversion model. The fractional conversion model represents the response rate required at a given time to complete a phenomenon. This modeling is necessary for designing online quality control systems for thermal processing in the food industry and preserving the apparent quality of the product by optimizing the most important drying parameters. In this study, the kinetic of color changes in apple slices was investigated, in order to maintain appearance quality of product during simultaneous infrared dry-blanching and dehydration with intermittent irradiation.
Materials and Methods: Apple slices (Golden Delicious Variety) were dried in three thicknesses of 5, 9 and 13 mm using three constant surface temperatures of 70, 75 and 80 ° C. Image acquisition of apple slices was made use of a flatbed scanner with an interval of 15 minutes during processing. The treated samples were placed on the scanner and then a black box was utilized so as to prevent the interferences of the peripheral lights. The images featured a 300 dpi quality and were saved in TIFF-24 bit format. The color analysis of the images was carried out in color space of L*a*b* by the use ImageJ software, version 1.6.0. The lightness parameter (L), redness (a), yellowness (b), the intensity of the color changes (∆E), chroma (Cr) and browning index (BI) were described during product processing using fractional conversion model. Equilibrium color parameters (Cf) were also used as an indicator to compare different process conditions. The fitting of the model was done using the curve fitting toolbox in the 2009 version of the MATLAB software with 95% confidence level (P
Hamid Bakhshabadi; Habibollah Mirzaee; Alireza Ghodsvali; Seyed Mahdi Jafari; Aman Mohammad Ziaiifar
Abstract
Introduction: Black Cumin seed (Nigella sativa L.) as one of the novel edible oil resources used commonly nowadays as seasoning in food product industries due to considerable medicinal properties and high nutritional impacts. Oil extraction by pressing method as an approach compared to other methods ...
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Introduction: Black Cumin seed (Nigella sativa L.) as one of the novel edible oil resources used commonly nowadays as seasoning in food product industries due to considerable medicinal properties and high nutritional impacts. Oil extraction by pressing method as an approach compared to other methods including solvent extraction is faster, safer and cheaper. In the oil extraction process, the preparation of the seeds is a substantial stage for obtaining oil with high quality and efficiency. Microwaves are electromagnetic waves that have a frequency ranged from 300 MHz to 300 GHz with corresponding wave lengths ranged from 1 mm to 1 m. On the other hand the artificial neural network as a powerful predictive tool in a wide scale of process parameters has been studied on an industrial scale in this research in order to achieve a simple, rapid, precise as well as effective model in the oil extraction of Nigella sativa L seed.
Materials and Methods: In the present study Black Cumin seeds after preparation including cleaning and passing resistance of the samples in front of air and moisture were stored in a plastic bag until the day of experiments. Then, they have been pre-treated with microwave within different processing times (90, 180 and 270 S) and powers (180, 540, and 900 W). Afterwards, seeds’ oil was extracted by screw rotational speed levels approach (11, 34 and 57 rpm). Different selected parameters including extraction efficiency, oil acidity value, color and oxidative stability were determined. To predict the alterations trend, the artificial neural network (ANN) design in MATLAB R2013a software was used.
Results and Discussion: According to MSE and R2 values obtained in this study, feed forward neural network with transfer function sigmoid hyperbolic tangent and Levenberg- Marquardt learning algorithm with topology of 3-10-5 (input layer with 3 neurons– a hidden layer with 10 neurons – output layer with 5 neurons) were selected as the optimal neural network with R2 more than 0.995 and MSE equal to 0.0005. Also, the results of the optimized and selected models were evaluated and these models with high correlation coefficients (over 0.949), were able to predict the changes' trend. According to the complexity and multiplicity of the effective factors in food industry processes and the results of this research, the neural network can be introduced as an acceptable model for modeling these processes. By determining the activation function in neural networks which was a function of sigmoid hyperbolic tangent in this study and also, with having the amounts of weight and bias, the connections created by the neuro-fuzzy model can be extracted. By defining this simple created mathematical equation, in computer software such as Excel, we can have a useful, simple and accurate program for predicting the desired parameters in the process of oil extraction by using microwave pre-treatment. Due to high accuracy of neural model we can trust the prediction of these models with high confidence, and this model can be used to optimize and control the process, which can lead to saving in energy and time, and on the other hand, can create a better final product.
Adel Dezyani; Aman Mohammad Ziaiifar; Seyed Mahdi Jafari; Mohammad Ghorbani; Alireza Sadeghi Mahoonak
Abstract
Introduction: High sensitivity of fruit and vegetables juices to heat has been resulted to the development of spray drying method for drying this category of products. Spray drying is a well-established and widely used method for transforming a wide range of liquid food products into powder form. The ...
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Introduction: High sensitivity of fruit and vegetables juices to heat has been resulted to the development of spray drying method for drying this category of products. Spray drying is a well-established and widely used method for transforming a wide range of liquid food products into powder form. The process involves spraying finely atomized solutions into a chamber where hot dry air rapidly evaporates the solution leaving the spray-dried particles. Spray-dried powders can be stored at room temperature for prolonged periods without compromising the powder's stability. Powders are cheaper to transport and easier to handle in manufacturing plants. Spray-dried powders are economical to produce compared to other processes, such as freeze-drying. Spray drying has many applications, particularly in the food, pharmaceutical and agrochemical industries. The conversion of high value food materials, such as fruit and vegetable extracts, into particulate form is not easy due to the presence of a high proportion of low molecular weight sugars in their composition which lead to the problem of stickiness. The particles stick to one another, to the dryer and to cyclone walls and remain there, forming thick wall deposits, while very little product comes out at the dryer's exit. This might lead to low product yield and operating problems. In general, the stickiness causes considerable economic loss and limits the application of spray drying on foods as well as on pharmaceutical materials. In order to reduce stickiness, different solutes have been used as carriers and coating agents for the spray drying. Some examples of these are Arabic gum, maltodextrins, starches, gelatin, methyl cellulose, gum tragacanth, alginates, pectin, silicon dioxide, tricalcium phosphate, glycerol monostearate and mixtures of some of them. Of these additives, maltodextrin offers a good compromise between cost and effectiveness. It has been found that it contributes to the retention of some food properties, such as nutrients, color and flavor, during spray drying and storage. On the other hand, the feed flow rate, the inlet and outlet air temperatures, atomizer speed, feed concentration, feed temperature and inlet air flow rate are important factors that have to be controlled in a spray drying process. Tomato paste is a typical example of a product that is very difficult to be spray dried due to the low glass transition temperature of the low molecular weight sugars present.
Materials and methods: This study was carried out to evaluate the effect of inlet air temperature of dryer (120, 150 and 180 °C) and concentration of drying aid or carrier agent of maltodexterin along with whey protein concenterate ratio of 4 to 1 (25, 37.5 and 50% w/w) on the quantitative and qualitative properties of tomato paste powder including moisture content, bulk density, solubility, powder morphology, amount of lycopene, and production efficiency. Response surface methodology was used to choose optimum conditions of the powder production process.
Results and Discussion:the results revealed that the production efficiency (not significant) and solubility (significant) were increased with increased higher inlet air temperatures of dryer; however, at these conditions moisture content (significant), bulk density (not significant) and amount of lycopene (significant) in the powder were decreased also higher concentrations of carrier agent increased the production efficiency, solubility and amount of lycopene in the powder; however, moisture content and bulk density of powder were decreased.
Conclusion: Optimal conditions in order to achieve maximum production efficiency, solubility, the amount of lycopene and the lowest moisture content of powder, bulk density were achieved at inlet temperature of 150°C and carrier agent concentration of (w/w) 50%.
Hadi Bagheri; Mahdi Kashani-Nejad; Mehran Alami; Aman Mohammad Ziaiifar
Abstract
Introduction: Roasting is one of the processing steps involved in the nut industry to improve the flavor, color, texture and overall acceptability of the product. Ppeanut is a fruit or pod of the order Leguminosae and contains 47–50% oil, 25–30% protein and is an essential source of minerals and ...
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Introduction: Roasting is one of the processing steps involved in the nut industry to improve the flavor, color, texture and overall acceptability of the product. Ppeanut is a fruit or pod of the order Leguminosae and contains 47–50% oil, 25–30% protein and is an essential source of minerals and vitamins; thus it makes a substantial contribution to human nutrition. Peanuts are readily acceptable as a cheap protein source and popular snack item that can be eaten alone or combined with other foods. Recently, peanuts have gained much attention as functional food and roasted peanuts is one of the most popular snack foods, in which roasting is a key step in the process and directly impacts the quality (crispness, taste, and flavor) and shelf-life of the final product. Understanding of the roasting process is of interest because roasting is a critical processing step not only for peanuts, but many other food products such as coffee, cocoa, grains and other tree nuts. Roasting is a process to develop color, flavor and textural characteristics of product through chemical reactions, therefore proper roasting is critical to flavor and texture development as well as nutritional content of the final product.
Materials and methods: In this study, dried Goli peanuts were supplied from a local market in Minodasht, Iran in 2015 and stored at 4°C until processing. The average moisture content of peanut kernels was measured as 5.1 % (d.b.). Kernels were sorted manually to get the uniform sizes for roasting. 100 g peanut kernels were soaked in 500 ml of 25% salt solution for 30 min. After soaking, the salt solution was drained using a strainer and the excess water was removed by a cloth filter. After soaking, the moisture content of soaked peanut kernels increased to 8.27 % (d.b.). For roasting, three temperatures (140, 160 and 180°C) and three times (10, 20 and 30 min) and constant air velocity (1 m/s) were applied. Roasting was performed in a hot air roaster equipped with a controller to adjust the roasting temperature. After roasting, the whole kernels were allowed to cool at room temperature (23 ± 2°C). Roasting process was performed in 3 replications. Instrumental texture measurements (Uniaxial compression test) were carried out at room temperature using a TA-XT Plus Texture Analyzer using cylinder probe (diameter 25 mm) on peanut halves. The textural parameters of peanut halves were expressed as fracture force (initial peak or first fracture force (N)), hardness (highest peak compression force (N)), initial tangent modulus or apparent modulus of elasticity that shows sample rigidity in the linear part of the force-deformation curve (N/m) and compressive energy or area under the curve for the compression that is the work (N×m) required to attain deformation, indicative of internal strength of bonds within product. Sensory attributes including colour, texture, flavor, odour, total acceptance and final acceptance were assessed according to a five-grade hedonic scale (5 points – the best, 1 point – the worst). A completely randomized factorial design was used to evaluate the results and analysis of variance (ANOVA) was carried out to compare the mean values. All significant differences were reported at P ≤ 0.05 levels. Minitab statistical software (Minitab Release 16, Minitab Inc., USA) was used for all statistical analyses in the present research. However, MSTATC (Version 2.10, Michigan State University) was used to determine significant differences.
Results & discussion: Roasting is one of the most important steps in peanuts processing that leads to the development of the desired aroma, taste, texture and color of the final product. The results showed that increasing the roasting temperature and time decreased the fracture force (75.19–45.92 N), instrumental hardness (81.74–48.90 N), apparent modulus of elasticity (7.508-5.446 N/s), compressive energy (469.0–199.1 N.s) and improved the sensory characteristics of peanut kernels. During roasting process, moisture content of peanut kernels decreased and they became more crumble and fragile which causes to break easier and moisture reduction helps to create a desirable crisp texture. The results of the consumer test showed that the roasted peanut kernels have good acceptability for color (4.50), texture (4.15), flavor (3.89), odor (4.05), total acceptance and final acceptance (3.97) on roasting temperature and time (160°C and 30 min). The results obtained for VIP coefficients (standard coefficients) in PLS regression for fracture force, instrumental hardness; apparent modulus of elasticity and compressive energy variables indicated that apparent modulus of elasticity could be able to predict the individual sensory attribute of peanut kernels except color. PLS results showed that apparent modulus of elasticity could successfully predict quality sensory characteristics of peanut kernels. Thus, instrumental apparent modulus of elasticity could be replaced with sensory analysis for evaluation the quality of peanut kernels.
Safie Khalilian; Aman Mohammad Ziaiifar; Ali Asghari; Mahdi Kashani-Nejad; Mohebbat Mohebbi
Abstract
Introduction: Thermal properties of food during the frying process and mass transfer mechanisms (water and oil) can help in controlling the quality of the fried product (Fiszman et al., 2005). During the frying process, heat was transferred from the oil to the sample surface that it increases the temperature ...
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Introduction: Thermal properties of food during the frying process and mass transfer mechanisms (water and oil) can help in controlling the quality of the fried product (Fiszman et al., 2005). During the frying process, heat was transferred from the oil to the sample surface that it increases the temperature almost to 100 °C, the water evaporates and moved out. The sample surface was covered by bubble layers with various size and distribution. The formation of vapor bubbles on the samples surface have been effective on the micro-flows which is one of the important factor in the coefficient of heat transfer (Sahin et al., 1999). Therefore, knowledge of the relationship between the boundary layer and the surface heat transfer coefficient can determine the thermal behavior and kinetics of the migration of moisture and oil. Eggplant (Solanum Melongena L.) is one of the major agricultural crops of Asian and Mediterranean countries. Iran after China and India has achieved third place in eggplant production, which has made it remarkable, and economical. Eggplant absorbs high amounts of oil during the frying process due to its high moisture content (more than 90%) and high porous structure even if the residual water content is still quite high after frying.
Materials and methods: Fresh eggplants (Solanum melongena L. family Solanaceae) were obtained from the local market and stored at 4°C. Eggplant samples were washed with water tap and cut with manual mold into equal and similar cylindrical pieces (2.5×1cm). They were then washed with distilled water and surface water was removed using tissue paper. Finally, the samples were packed by poly-ethylene in order to prevent surface drying. A commercial sunflower oil was purchased from Ladan Factory, Iran.
Eggplant samples were dried at different temperature of hot air drying 40, 70, 100 and 130°C until moisture content 5 and 12 db%. Samples were drawn from the drier after drying, cooled at room temperature (25°C) and deep fat fried.
A domestic deep fat fryer with temperature control of ± 1°C (Seb, France) was used for carrying out frying operations. The fryer was filled with 2.5 l sunflower oil. The eggplant to oil ratio was kept at 1:50 w/v to reduce temperature variation in the oil bath. The frying was performed at 130, 150 and 170 °C for regular interval times 1, 2, 3, 4, 5 and 6 min. The frying oil was changed after 10 h of frying time. The samples were immediately removed from oil and were located on wired plate for draining and remove excess oil on the surface, and allowed to cool at room temperature before analyses. All experiments were performed in triplicates and the presented results are the mean of the obtained values.
Oil and moisture content were determined according to AOAC, 1995.
K type thermocouples (copper-nickel) with accuracy of ±1°C were used to measure the temperatures of samples. Temperature acquisition TC-08, Pico® (Technology Limited, England) with accuracy ±0.5°C and temperature controller PID Rex- D-100® (RKC) were used to data collection and oil temperature control, respectively.
In this study, convective heat transfer coefficient was calculated between surface sample and oil according to Farinu and Baik (2008).
In order to predict surface heat transfer coefficients and mass transfer kinetic eggplant samples during deep frying was used artificial neural networks. Then, the 4 inputs including: frying temperature (130, 150 and 170 °C), frying time (1, 2, 3, 4, 5 and 6 min), 4 pre-treatments drying temperature by hot air (40, 70, 100 and 130 °C) until the two moisture levels (5 and 12 %db) were used and output parameters including moisture and oil content, heat transfer coefficient with two replications which in total of 288 data were used to form the network structure.
Results and discussion: Results of this study showed that there is some complicated relationship between convective heat transfer and moisture and oil content. In addition, the convective heat transfer coefficient in up and down surface of the sample showed that oil absorption will be from upper surface. This phenomenon can be attributed to upper surface due to more bubbles of vapor out of the sample. This leads would slower the formation of crust on the upper sample. Finally, channels and cavities of the upper level will be more susceptible to the contact of oil. The results of predictive parameters of heat and mass transfer during deep frying eggplant samples using artificial neural network multilayer perceptron as a non-linear method showed closely relationship with experimental data. It indicates that the proper functioning of this method for modeling and studying the relationship between heat and mass transfer phenomena during deep frying of eggplant samples.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
Introduction: Frying phenomena occur during the immersion of the product in oil at a temperature of 150–200 ºC, where a simultaneous heat and mass transfer take place. This is the most popular thermal processes of potato cooking. This fast drying is critical to improve the mechanical and structural ...
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Introduction: Frying phenomena occur during the immersion of the product in oil at a temperature of 150–200 ºC, where a simultaneous heat and mass transfer take place. This is the most popular thermal processes of potato cooking. This fast drying is critical to improve the mechanical and structural properties of the final product. These conditions lead to high heat transfer rates, rapid cooking, browning, texture and flavor development. The fried potato is easier to transport and provides better texture. Researchers have assumed the existence of two regions for fried product, separated by an interface: the core (unfried) and crust (fried) regions. In general, frying process is very complex for two main reasons: i) due to the simultaneous heat and mass transfer between food material and frying oil, ii) due to the progressive deterioration of the oil and structural changes in foods (crust and core regions). The moving boundary problem may be found in many areas of frying research involving heat and/or mass transfer. In this study, heat and mass transfer is entirely investigated during frying of potato strips. The transport phenomena during frying are including: i) Heat convection from the hot oil to the interface via the crust region, ii) Water evaporation at the moving interface at a temperature of 100 ºC, iii) The unsteady state heat conduction in both regions of crust and core, iv) The oil uptake into food. As a result, high temperature and low moisture conditions develop as frying proceeds. Water vapor bubbles escaping from the surface of the food cause considerable turbulence in the oil. Therefore, Heat and mass transfer are dependent on each other during frying process. In fact, heat and mass transfer during frying can be controlled by heat transfer at the product surface. Evaporation rate depends on the temperature difference between oil and boiling point of water. There is little information on modeling, both empirical and phenomenological, for moisture loss and oil uptake during frying. Knowledge of accurate heat and mass transfer parameters is important for modeling processes. Designing of frying processes is possible through the use of mathematical models. The aim of this study is to develop a more completely and realistic approach for determining of heat and mass transfer parameters and their relation to oil temperatures. The main process parameters influencing oil uptake are frying temperature and duration. Heat transfer coefficients for different oil temperatures determined using simple method. Mass transfer of water was assumed to be governed by Fick's law of diffusion. For more details, empirical models were used to describe the mass transport in forms of moisture and oil.
Materials and Methods: The frying operation of potato strips was performed in the fryer that was equipped by thermo controller system with K type thermocouple at three different oil temperature of 145, 160 and 175 ºC for 60, 120, 180 and 240 seconds. The core temperature changes of product recorded on computer during process using T type thermocouple connected to data logger. The moisture and oil content of samples measured for each process time and temperatures. The heat and mass transfer parameters such as kinetic coefficients of moisture (Km) and oil transfer (Ko), mass transfer coefficient (Kc), effective diffusivity (D) and heat transfer coefficient (h) were evaluated with dimensionless temperature and concentration ratio plots and also empirical equations. Relationship of these parameters to the temperature of the oil investigated using the Arrhenius equation. Thermal conductivity of potato strips during frying determined as a function of moisture content using the Anderson and Spell equations.
Results & Discussion: The results showed that mass transfer Biot number (Bim), mass transfer coefficient (Kc) and effective moisture diffusivity (D) increased significantly with increasing in oil temperature. In regression models, the linear correlation between kinetic constant of water loss and oil uptake was observed that is verification on effect of drying pretreatment on reducing oil uptake. In fact, with increasing of oil temperature the kinetic constant of water loss increased and caused increased in kinetic constant of oil uptake. Kinetic models could correctly confirm determination of mass transfer parameters. The heat transfer Biot number (Bih), convective heat transfer coefficient (h) and product thermal conductivity (k) decreased significantly with an increase in process temperature. With increasing in the rate of evaporation, following greater amount of input energy used for water loss. This would reduce the amount of available energy to increase internal energy of product and thus reduce the convective heat transfer coefficient at high temperatures. Frying process caused remove of water from product and increasing of porosity, thus observed gradually fell in thermal conductivity. Although the minimum thermal conductivity at various temperatures are close together, but two equations of Anderson and Spell showed significant difference for values of thermal conductivity and Spell was more close to published papers. High activation energy is achieved for lower moisture content that is normally due to the strong water-substrate interaction.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad
Abstract
Introduction: Texture is one of the most important attribute in foods and is always issues for the manufacturing of fried products, because texture plays a crucial role in consumer acceptance and the perceived quality of foods. Prediction of changes in texture during frying can be helpful in process ...
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Introduction: Texture is one of the most important attribute in foods and is always issues for the manufacturing of fried products, because texture plays a crucial role in consumer acceptance and the perceived quality of foods. Prediction of changes in texture during frying can be helpful in process control. Structurally, this quality parameter in fried potato strip made from the formation of a composite structure with two layers as: dry and oily outer layer (crust), and a moist or soft interior layer (core). So, the explanation of texture development during frying is difficult because of the innate heterogeneity of the fried potato tissue. Moreover, both thermal degradation and texture development are functions of variables such as processing time, oil temperature and vaporized moisture of product. Textural changes during frying described as the result of various physical, chemical, and structural changes involved in the frying process. One solution to reduce the complexity of real bio systems in engineering is using various empirical correlations. Application of these relations for prediction of textural changes during frying can help us for understand the proper conditions to achieve desired texture. The purpose of the present investigation was to study the influence of the frying temperatures on texture of potato strips. In fact, textural changes during various stages of frying potatoes including initial heating, surface boiling and falling rate period were investigated. Texture evaluation is done by mechanical measurements, because the stimulus in texture perception is mainly mechanical. Also, textural studies are not clearly performed up to now with focus on cook value as a main factor in potato frying. According to the definition of cook value, this parameter indicates total time of baking in 100 °C. Fractional conversion applied as a technique for analyzing texture degradation kinetics and softening of vegetables upon prolonged heating. A few assumptions were made during study: i) Potato shrinkage is neglected ii) Product is not completely dried iii) The stages of frying were considered separable only based on surface and center temperature iv) Texture of potato strips affected by cook values of each frying stages. Materials and methods: The potato strips with specified size fried at a constant temperature of 145, 160 and 175 °C for 30, 60, 90, 120, 150, 180, 210 and 240 seconds. Then, various stages of the process were separated using surface and center temperature profiles of product that were recorded by data logger and T-type thermocouple in computer. Heating extremity of each stage was determined using cook value parameter. Mechanical properties such as apparent modulus of elasticity (Secant modulus) and toughness were used to show which occurred during frying. The secant modulus (S) variations described using fractional conversion model. The degree of cooking for each sample was expressed in term of cook value and its relationship with the overall acceptance of product was examined. Finally, the suitable temperature was determined by sensory evaluation to achieve the desired texture to determine the proper cook value and to prevent over cooking of product. Results and Discussion: The stages of frying by immersion for experimental conditions can be divided as: I. Initial heating (The first 30 seconds for all oil temperature) II. Surface boiling (30-60 s). III. Falling rate (up to end, longest period). IV. Bubble end point (not considered). Generally, higher oil temperature showed larger center and surface cook values because of the fast temperature increase inside product. During initial heating period (I) because of temperature increase without boiling, the changes in cook values versus time are negligible. Surface cook value increased slowly compared with core during surface boiling. Maximum cook value for core temperature was higher, because of the vapor pressure at the center of the product and thus water evaporation at temperatures above 100 °C (cook value above 1 second). During falling rate period due to gradual reduction of evaporation rates, and thus the vapor pressure drop within product, boiling temperature reduced to 100 ° C. The major part of texture destruction occurred during initial heating period and the changes of textural characteristic were going to be constant at the end of surface boiling. The slope of the regression line for fractional conversion model decreased as temperature increased and therefore product was harder, but equivalent value of secant modulus was independent of process temperature. The consumer texture desired was found for temperature of 160 °C with medium cook value. The kinetics of potato softening followed an exponential decay equation with good correlation on empirical data. The temperature dependence of the degradation rate was reliably modeled by the Arrhenius equation. Activation energy (Ea) for model parameters Se and Ks was 13047.12 and -24949.74 J/mol, respectively. Negative Ea for kinetic constant (Ks) indicated an inverse relationship with oil temperature. In addition, elevated oil temperatures caused less softening of French fries because of higher cook value and thus higher evaporation rate.
Azadeh Ranjbar Nedamani; Aman Mohammad Ziaiifar; Mahdi Parvini; Mahdi Kashani-Nejad; Yahya Maghsoudlou
Abstract
Introduction: Canning is the most effective way to food preservation. Starch- based foods include the major food materials such as porridges. These foods due to sensitivity to high shear rates used in rotary retorts and thus texture decomposition, usually sterilized in static retorts. Broken heating ...
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Introduction: Canning is the most effective way to food preservation. Starch- based foods include the major food materials such as porridges. These foods due to sensitivity to high shear rates used in rotary retorts and thus texture decomposition, usually sterilized in static retorts. Broken heating behavior, can headspace and initial temperature have important role on heat transfer rate and the position of cold area in these products. Heat breaking phenomena in the thermal curve, which can be seen in foods containing starch, is essentially related to gelatinization and destroying of starchgelstructure. Starchmaybe naturally exist in foods ormay be added to food formulations as an additive to create the consistency, filler, volumeproviders, emulsionstabilizer and etc. However, during thermal processing of foodscontaining high amounts of starch, complexstructural changes occur which leads to viscosity increases. These changes aredue to structural changes of starch during gelatinization; such as irreversible swelling of the starch granules, melting of starchcrystals, leaking of starch granule compound. Depending on thetype of starch and its concentration, the final product can bean aqueous solution or agel structure. Increasing in starch viscosity after gelatinization leads to decrease in heating rate, but with the advancement of heating time, when most granule swelling occurs, and the granules are being disrupted and the viscosity is reduced. This leads to increase the heating rate. This dual behavior of starch dispersion viscosity, leads to break in heating curve. Such solutions are named broken heating curve foods.The aim of this study was numerical simulation of the effect of starch concentration and initial temperature on heat transfer rate of starch dispersion during static sterilization with COMSOL software. Materials and methods:To prepare 100ml of 3.5 and 5% starch dispersion, 3.5 and 5 g starch was dissolved in 96.5 and 95 ml distilled water at 24.7C, respectively. The solution was then heated at 50C for 10 min to avoid sedimentation during the heat process. Samples were filled at 50 and 75C initial temperatures. In each can (9.9×10.1cm), T- type thermocouple was placedin one-third length from the bottom. All measurements were performed in triplicates. The 8-port data logger (Pico-TC08, England) and related software (PicoLog) were used to record the temperature data with 10s intervals.The full filled cans (without headspace) were statically heated in vertical position with no rotation. Numerical solutions of the governing equations were performed by COMSOL Multiphasics 4.2b software. A BDF method for time stepping and Backward Euler to time discretization were used. The system used to run the test and solve the equation was Intel VR CoreTM i5CPU M 460 @ 1.70 GHz and 6GB RAM. Numerical simulation of COMSOL software include spairing two physical phenomena: heat transfer and fluidflow. Since the system was cylindrical shaped can contain food with natural convection, non-isothermal laminar flow equationswere used. For this problem, one geometry and two domains were defined. The governing equations for non-isothermal laminar flow for domains were defined. Since in thermal diffusion analysis, the formula methods are more correct than empirical methods, formula methods were used in this study for calculating j and f. The accuracy of these calculations was evaluated using CFD. Parameter - f is the slope of heating curve. Jhindex, as a dimensionless correction factor. Results and discussion: The results showed that thecold area is near theone-tenth ofcans bottom. Inboth product initial temperatures, varying the concentration of the starch in product from 3.5 to 5% leads to longer heating time. The increase in the thermal process time at one-tenth of can bottom is more than one-third of can bottom. The time which the dispersion reaches to static temperature also changes with starch concentration in dispersion. The temperature difference in 5% starch dispersion at static temperature at the end of heating process is more considerable than 3.5% starch dispersion. Higher starch concentration induces a decrease in f (The fh coefficient represents thetime required to move heating process one cycle in heating curve and it can be calculated from the slope of the linear part of heat curve) at one-third of can bottom while an increase in f at one-tenth of can bottom. This behavior can be related to the fact that the starch gelatinization takes place earlier in one-third of can bottom than one- tenth due to the faster increase in temperature.
Hassan Sabbaghi; Aman Mohammad Ziaiifar; Alireza Sadeghi Mahoonak; Mahdi Kashani-Nejad; Habibollah Mirzaee
Abstract
Introduction: Heat transfer processes are important for almost all aspects of food preparation and play a key role in determining food safety. Temperature difference between the source of heat and the receiver of heat is the driving force in heat transfer. Convection is the transfer of heat by the movement ...
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Introduction: Heat transfer processes are important for almost all aspects of food preparation and play a key role in determining food safety. Temperature difference between the source of heat and the receiver of heat is the driving force in heat transfer. Convection is the transfer of heat by the movement of groups of molecules in a fluid. The groups of molecules may be moved by either density changes or forced motion of the fluid. In a typical convective heat transfer a hot surface heats the surrounding fluid, which is then carried away by fluid movement. The convection heat transfer coefficient or h value is defined as the rate of heat that will be convected at the product surface–fluid interaction through a unit surface area of the material if a unit temperature gradient exists between the product surface and the surrounding fluid and is very important in modeling and design of frying systems for foods. Frying is a very turbulent process with random and dynamic movement of small bubble particles over the boundary layer of the product surface. Deep fat frying is a very fast method of food processing among conventional heat transfer methods. The frying by immersion can be divided into four stages: (1) initial heating (the temperature of the internal part is slowly increased to boiling point); (2) surfaces boiling (crust formation and higher oil turbulence); (3) falling rate (long period, vapor transfer at the surface decreases) and (4) bubble end point (dried product). These four states during frying can be generalized as non-boiling phases (stages 1 and 4) and boiling phases (stages 2 and 3). So, Convection heat transfer during immersion frying may be divided into two stages: 1) free convection during initial heating of the material and 2) forced convection during the boiling phase. In this study, the convective heat transfer coefficient investigated as a function of the water loss rate during frying process due to the effects of evaporation and boiling on this thermal parameter. Understanding of changes in heat transfer coefficient for thermal control of the frying process is very important to achieve optimum quality of product. Materials and Methods: The potato stripes with specified size are fried at temperature of 145, 160 and 175 °C for 60, 120, 180 and 240 seconds using sunflower oil. The center and surface temperatures of potato stripes were recorded with two-second intervals using T type thermocouple and data logger. Moisture content of French fries was measured by drying them within an oven instrument. Mean moisture and oil content of potato stripes was measured. The h value was estimated and its changes studied during process using heat energy balance between the sample and oil by assuming that total heat transferred by convection from oil to potato is equal to the sum of energy spent on heating potato and energy spent on water evaporation. Moreover, changes in the fraction of total heat used for evaporation at different temperatures were expressed as an empirical model. Results and Discussion: The results showed that the temperature at the center increased up to the evaporation temperature (“A” zone: about 60 seconds after process beginning). Then, it remained constant at this temperature for a while due to evaporation (“B” zone: about from 60 s till 160 s). This constant temperature period decreased as temperature increased. After this period, the center temperature approached to that of oil (“C” zone: increasing product surface temperature to oil temperature). These various stages of the process were separated. The moisture loss rate was high at the beginning of frying and oil uptake increased as the moisture content diminished. As oil temperature increases, the sample moisture content for the same frying period decreases since an increase in temperature results in a higher kinetic energy for water molecules leading to a more rapid moisture loss in form of vapor. The heat transfer coefficient is increased as the oil temperature increased and at the first time of process observed higher h value. It was due to more water loss rate and so the higher turbulence within the oil before crust formation and for elevated temperatures. The maximum heat transfer coefficient for the temperatures of 175, 160 and 145 °C is estimated 943.68, 847.81 and 682.64 W/m2°C, respectively. Estimated h value also shows a linear increase with water loss rate. Since most of the energy used is associated with the evaporation of water present in the potato, for lower temperatures, the fraction of total heat needed to complete the evaporation is higher and it also represents lower h values by reducing the oil temperature. Also, the variation in the fraction of total heat used for water evaporation showed exponential rise to maximum behavior. Conclusion: The proposed model for studying evaporation heat fraction fitted experimental data properly, with standard error values range of 0.01-0.03. Evaporation heat fraction could have been affected by oil temperature changes, water loss rate and h value (linear depend with the water loss rate) during process.
Masoud Hashemi Shahraki; Aman Mohammad Ziaiifar; Mahdi Kashani-Nejad; Mohammad Ghorbani
Abstract
Oil uptake occurs mainly during cooling immediately after frying. Post-frying centrifuge step used to remove the attached oil to the surface of friedproduct. Response surface methodology (RSM) technique was used to develop models for the responses to the centrifugal force (100, 200 and 300 rpm) and centrifugal ...
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Oil uptake occurs mainly during cooling immediately after frying. Post-frying centrifuge step used to remove the attached oil to the surface of friedproduct. Response surface methodology (RSM) technique was used to develop models for the responses to the centrifugal force (100, 200 and 300 rpm) and centrifugal time (20, 50 and 80 s), frying temperature (140, 170 and 200 C) and frying time (4, 6 and 8 min), Investigated factorsoptimized with respect totheoil and moisture contents, color and textural parameters. The models showed very well fitness with experimental data. The coefficients of obtained models with RSM, was optimized by using genetical gorithms and was observedthat GA optimized models showingbetterfitnesswith theexperimentalresults than RSM models. The resultssuggest thatpost-frying centrifuge step in300 rpm for 80 sand fryingin 175-180Cfor 7-8 minleadsto French fries withlowestmoisture and oil contentand best color and texture.
