Food Technology
Behshad Tahani; Babak Beheshti; Mohsen Heidarisoltanabadi; Ehsan Hekmatian
Abstract
Introduction
Isfahan province is considered to be one of the top ten producing provinces of apple orchards with an area of 17,274 hectares and a production of 120,000 tons of apple. Determining the quality parameters of agricultural products requires the use of various methods, which are different according ...
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Introduction
Isfahan province is considered to be one of the top ten producing provinces of apple orchards with an area of 17,274 hectares and a production of 120,000 tons of apple. Determining the quality parameters of agricultural products requires the use of various methods, which are different according to the nature and characteristics of each product. The two main categories for dividing these methods include analytical (objective) methods and sensory (intrinsic) methods. Both qualitative assessment methods can be used in destructive and non-destructive ways. Apple is one of the fruits that can be stored for a relatively long time. Physiological changes during the storage period are inevitable and cause change to some quality characteristics of the fruit, such as firmness, moisture content, density, pH, and soluble solids. Using the methods of determining and extracting the quality characteristics of fruit during storage and monitoring the changes created, provides a suitable criterion for selecting and preparing the necessary conditions for storage and storage at the disposal of users and producers. X-ray imaging technique is among the methods used and computed tomography, which is now well-known in evaluation of various agricultural commodities and food quality. X-rays are electromagnetic waves with a short wavelength (0.01 to 10 nm) and high energy (from 120 electron volts to 120 kilo electron volts) that can penetrate many materials.
Materials and Methods
In order to determine the relationship between the physicochemical properties and the CT number of Golden Delicious apples, 280 Golden Delicious apples were collected from an orchard located in Semirom city of Isfahan province and stored in a cold room at 0 and 4 ºC and a humidity of 85±5%. These apples were harvested and collected from several trees after the fruit ripened completely. The weight and volume of apples were randomly selected based on the apples on the trees. The samples of stored apples were examined in 4 stages and based on the duration of storage on zero (the beginning of storage), 45, 90 and 135 days.. These tests included non-destructive tests of CT scan imaging and destructive tests to extract the physicochemical properties of apples, including CT number, pH, firmness, moisture, density, and soluble solids. In order to prepare CT scan images of apple samples (non-destructive X-ray test), a GE Healthcare multi-slice CT scan machine model 5122080-12 with 80 kV and 10 mA was used in the CT scan center of Al-Zahra Hospital in Isfahan. Moisture content was determined by weighing the samples and recording their moisture changes before and after drying in the oven at 105 ºC s for 24 hours. Total soluble solids were measured by refractometer device and reported as Brix degree. In order to measure the density of fruits, the weight and volume of each fruit was recorded. A digital pH meter was used to measure the pH of fruit. Penetrometer device was used to measure the firmness of apples. At the end, with the specified values, Pearson correlation coefficients between CT number and other physicochemical properties were determined. Also, by plotting the mentioned values, the most suitable regression equations with the highest coefficients of determination were obtained.
Results and Discussion
Based on the results, the average value of CT number, pH, firmness, moisture, density and total soluble solid of apple at two temperatures of zero and 4 ºC were -115.02 and -166.86, 3.85 and 3.86, 76 37.36 and 33.36 N, 0.82 and 0.80%, 0.76 and 0.72 g/cm3 and 15.30 and 15.79% Brix, respectively. The results showed that the CT number has a negative linear correlation with pH and total soluble solid and a positive linear correlation with the properties of apple firmness, moisture and fruit density. Based on the results, at two storage temperatures of 0 and 4 ºC, the coefficients of determination (R2) obtained from the linear regression model of CT number with pH levels of 0.75 and 0.55, apple firmness 0.32 and 0.57, moisture content 0.78 and 0.85, fruit density 0.82 and 0.84 and total soluble solid 0.85 and 0.62 were obtained.
Conclusion
These results shown that the non-destructive test of X-ray imaging can be used with a suitable approximation to determine some quality properties of apple products.
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.
Sepideh Aryaee Majd; Mania Salehifar
Abstract
Introduction: Donte is one of the most important fermented products in all over the world which similar to bread, after ferret fermentation process, dividing, shaping and rest of the dough, it would be frying in the oil instead of baking in the oven. We feel the need of using food additives (such as ...
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Introduction: Donte is one of the most important fermented products in all over the world which similar to bread, after ferret fermentation process, dividing, shaping and rest of the dough, it would be frying in the oil instead of baking in the oven. We feel the need of using food additives (such as antioxidants, enzymes and etc.) in order to produce such high quality products with long shelf life because of industrialization of donut, large function production and increasing customer demand. The antioxidant compounds causes the food to have long-lasting shelf life and this results in producing a practical product. This research was carried out to evaluate effects of apple extract(in quantities of 8,10,12% ) and pimento extract (in quantities of % 5/1، 5/2، 5/3) as a rich source of Antioxidant affecting the rheological paste properties including the Farinography test, physicochemical properties such as hardness in periods of 1 to 3 days, humidity and color, shelf life index including peroxide in three periods of 1 , 15, and 30 days after cooking, DPPH and total Phenol inhibition tests and sensory evaluation of the product. Effects of the extracts on the rheological dough has shown that apple and pimento influencing the Farinography factors caused. Moreover none of these extracts had a meaningful effect on the index of paste quality. Result of phytochemical evaluation indicated that the hardness in two periods of 1 and 3, color value indicated, peroxide index and total acceptance decreased as the apple and pimento increased. The humidity content increased as the apple and pimento were used more. The result of DPPH and total Phenol inhibition tests showed that the pepper extract in DPPH free radical control was more successful than apple extract, and the amount of phenolic compounds in pepper extract was 2.4 more than apple extract. All experiments were replicated three times Optimized conditions included the use of 11.95% apple extract and 3. 3% sweet pepper extract in donut dough formulation. Generally addition of plant extracts can decrease oxidation speed of donut effectively.
Materials and methods: Include procedures and method of producing donut and methods of extracting apple and pimento also include test to measure flour such as moisture, ash, acidity, pH and protein and moisture, hardness, color, peroxide index, farinografy test, Total phenol and DPPH free radical inhibitory. The statistical population includes different levels of apple and pimento extracts, measured parameters have been studied by using simple line and polynomial equations 2 and 3.After testing in research methodology and data extraction, data analysis was carried out using RSM method and Design Expert 8 and statistical significance was set at (p<0.05) All results have been made 3 times, on average.
Results & Discussion: The effects of the extracts on the rheological dough has shown that apple and pimento influencing the Farinography factors caused an increase in water absorption, and pimento reduced the stability, development time and increased the degree of softening. Moreover none of these extracts had a meaningful effect on the index of paste quality. It should be mentioned that the aforementioned effects are more influenced by the apple extract Result of phytochemical evaluation indicated that the hardness in two periods of 1 and 3 decreased as the apple and pimento increased. The humidity content increased as the apple and pimento were used more. The result of low light color value indicated that L* decreased by increasing apple and pimento extracts, which this had no impact on a* and b* color indexes. The result of shelf life tests showed that by increasing the amount of apple and pimento extracts in donut samples in two periods of 5 and 30 days caused decrease peroxide index and The result of DPPH and total Phenol inhibition tests showed that the pepper extract in DPPH free radical control was more successful than apple extract, and the amount of phenolic compounds in pepper extract was 2.4 more than apple extract. The sensory evaluation results showed that the increase in apple and pimento caused reduction in total acceptance of the produced. All experiments were replicated three times Optimized conditions included the use of 11.95% apple extract and 3. 3% sweet pepper extract in donut dough formulation. Generally addition of plant extracts can decrease oxidation speed of donut effectively.
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
Mohammad Reza Asghari; Raheleh Jami; Alireza Farokhzad
Abstract
Introduction: Nowadays, due to mechanization of life, consumers need of food which they spent little time for preparation, So Fresh cut industry is growing rapidly in the world. These products had strong growth since 1940, and in 2013, most sales of fresh cut fruit related to apples, against 21.8 percent. ...
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Introduction: Nowadays, due to mechanization of life, consumers need of food which they spent little time for preparation, So Fresh cut industry is growing rapidly in the world. These products had strong growth since 1940, and in 2013, most sales of fresh cut fruit related to apples, against 21.8 percent. Minimal processing operations include grading, washing, sorting, slicing, chopping and then packaging of fruit or vegetables. Since these operations result in quality loss, due to water loss, softening, microbial contamination, increased respiration, ethylene and tissue browning. To extend the shelf life of fresh cut fruit, some effective techniques including, low temperature, modified atmosphere packaging, nanotechnology and coating have been applied. Nowadays, edible coatings are used for fresh cut fruits to reduce respiration and control physiological changes. Nano-scale ingredients lead to increase surface to volume ratio so increases the activity of the particles and their impact, the other hand use of calcium compounds in the fruit can be caused strength of the cell wall and bridges between pectin polymers in cell wall and cell membrane so the activity of digestive enzymes decreases. Materials and methods: Golden delicious apples were selected for uniform size and appearance in a commercial orchard in Urmia. Fruit disinfected with disinfectant solutions for 10 min. half of the apples in the laboratory before cutting were immersed in nano calcium carbonate solution at concentrations of 0, 0.1, 0.2, and 0.4 % for 4 min and the other half of the fruit after cutting treated with the same concentrations of nano calcium carbonate for 2 minutes. Control fruit were treated with distilled water. Fresh cut were dried at 20 ᵒC for 15 minutes and placed in plastic containers (8 slices per a dish), In Refrigerator equipment at 1±0.5ᵒC and relative humidity 90-95% for 20 days. Results and discussion: Fresh cut apples coated with nano calcium carbonate reduced the enzyme activities. So that in treated samples compared to control samples polyphenol oxidase activity was reduced. Also, antioxidant activity and catalase levels were higher than the treated fruit during storage. As a result, fresh cut apples coated with nano calcium carbonate can be used as an easy way to increase the shelf life of apples in cold storage.
Latifeh Pourakbar
Abstract
Introduction: Lipid oxidation is a major cause of food quality deterioration during storage of oils, fats and other fat-containing foods. Oxidation of lipids results in changes that may affect the nutritional quality, wholesomeness, colour, flavour and texture of food. Moreover, the products of lipid ...
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Introduction: Lipid oxidation is a major cause of food quality deterioration during storage of oils, fats and other fat-containing foods. Oxidation of lipids results in changes that may affect the nutritional quality, wholesomeness, colour, flavour and texture of food. Moreover, the products of lipid oxidation may be potentially toxic and may lead to adverse effects such as the production of carcinogens, mutagenesis and aging. Autoxidation occurs when molecular oxygen reacts with unsaturated lipids. The process involves a free radical chain reaction that is most frequently initiated by exposure of unsaturated lipids to light, heat, ionizing radiation, metal ions or metalloprotein catalysts. Free radicals are defined as any chemical species having one or more unpaired electrons. Antioxidants are a group of chemicals capable of extending the shelf life of food that contain lipids. They are used to retard the development of unpleasant flavour caused by the oxidation of unsaturated fatty acids. They retard oxidation of lipids by reacting with free radicals, chelating free catalytic metals and also by acting as oxygen scavengers. Currently the food industry uses synthetic antioxidants such as BHA, BHT and TBHQ to retard lipid oxidation. However, there is concern about the safety and toxicity of synthetic antioxidants in relation to their metabolism and accumulation in body organs and tissues. Synthetic antioxidants are known among other things to cause impairment of blood clotting, lung damage and to act as tumor promoters. As a result of this, consumers have a preference for natural ingredients and there is a growing interest in the potential use of antioxidants from natural sources. Phenolic extracts from herbs and spices, cereals and legumes have been reported to effectively retard lipid oxidation in oils and fatty foods. As a result of concern for the safety of synthetic antioxidants, there is a growing interest in the potential use of phenolic extracts from plant sources as antioxidants in lipids. The potential use of phenolic extracts from different plant sources such as sorghum, herbs and spices have been studied extensively. Extracts of spices such as rosemary and sage are now available commercially for use as natural antioxidants. Phenolic compounds are defined as substances possessing a benzene ring bearing one or more hydroxyl substituents, including their functional derivatives. There are different sources of phenols such as grapes, olive oil, sorghum, beans, spices and herbs. Phenols have many favourable effects on human health. They decrease the risk of heart diseases by inhibiting the oxidation of low-density lipoproteins (LDL). A large range of low and high molecular weight phenols exhibiting antioxidant properties have been studied and proposed to be used as antioxidants against lipid oxidation. This is particularly true for those phenolics with multiple hydroxyl groups that are generally the most efficient for preventing lipid oxidation. Phenolic compounds are also known to possess antibacterial, antiviral, antimutagenic and anticarcinogenic properties. Generally the efficacy of phenolic compounds as antioxidants depends on a number of factors such as the number of hydroxyl groups bonded to the aromatic ring, the site of bonding, mutual position of hydroxyls in the aromatic ring and their ability to act as hydrogen or electron donating agents and free radical scavengers. All polyphenols are capable of scavenging singlet oxygen and alkyl radical through electron donating properties, thus generating a relatively stable phenoxyl radical. The goals of this study were to investigate the effect of incorporation of different apple cultivars’ phenolicextracts onformation of primary oxidation products in buttercomparing tosome of thesynthetic antioxidants such as BHA and BHT Material and methods: Different apple cultivars from different places of West Azerbaijan province had been collected and their total phenol content, flavonids and antioxidant properties were measured according to Folin-Ciocalteu, Colorimetry and Diphenylpicrylhydrazyl (DPPH) methods respectively. The measurement of peroxide value and thiobarbituric acid of local butter oil samples consisting of different concentrations of extract and synthetic antioxidants was performed as well. Discussion & Results: In conclusion, this investigation demonstrates that apple is a rich source of phenolic compounds and antioxidant capacity.Fuji and Sheikh Ahmad cultivars showed the maximum and minimum content of total phenol content, flavonoids and antioxidant activity which are 2940.24 and 1350.22 microgram equivalent gallic acid/ gram of dry extract; 2530.32 and 1200.74 microgram equivalent quercetin/ gram of dry extract and 91.87 and 32%. The maximum and minimum amount of peroxide value and thiobarbituric acid was reported for control and 400 ppm apple extract samples respectively. The results of this study showed that "Fuji" cultivar contained the highest antioxidant activity.The Fuji apple extract are able to reducethe formation of hydroperoxides in butter oil during storage at 6ooC. The phenolic extracts from Fuji apple to be more effective than BHA in stabilising butter oil at 60ºC. Apple phenolic extracts inhibited oxidation of butter oil. Theextracts were able to retard oxidation because of the ability of phenolic compounds toscavenge and stabilise lipid radicals by donating hydrogen atoms.Also the concentration of the extract was an effective factor in the inhibition of oxidation; that is, as we increased the concentration, the inhibition of oxidation also increased. Conclusion:: Due to their ability to act as reducing agents, phenolic compounds in apple phenolic extracts from Fujivarieties can be used as antioxidants in butter oil toretard formation of primary oxidation products, specifically hydroperoxides.
Omid Doosti Irani; Mahmood Reza Golzarian; Mohammad Hosein Aghkhani; Hassan Sadrnia
Abstract
Introduction: High percentage of orchard products, such as apples, is wasted due to mechanical damages that cause fruit quality loss. Damages due to static or dynamic pressure or impact are among very common mechanical damages that begin to bruise fruits. Post-harvest bruise damage is a major cause for ...
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Introduction: High percentage of orchard products, such as apples, is wasted due to mechanical damages that cause fruit quality loss. Damages due to static or dynamic pressure or impact are among very common mechanical damages that begin to bruise fruits. Post-harvest bruise damage is a major cause for the loss in fruit quality. Bruising means damaging fruit tissue and consequently physical changes resulting in fruit color and chemical changes resulting in fruit tastes (Xing and Baerdemaeker, 2005). Most research projects conducted on apple bruising have focused on the use of image processing techniques for detecting apple surface defects from images. In addition to images taken in visible spectral range, thermal images have been also used for this purpose. Having reviewed the literature and research gaps in this area, we set two hypotheses for this research project: first, the color characteristics of bruised tissue would change over time and these changes would be detectable on the images taken from the affected fruits. Second, there would be a significant difference between the surface temperature of bruised and sound tissues. The distribution of temperature on an impact-caused bruised tissue would change over time in a different manner compared with that for a sound tissue. The color and temperature variation is particularly related to the intensity of impact caused bruising and where the impact is applied on apples. Therefore, the first objective of this paper was to study the color changes on the tissues bruised from the impacts with three energy levels applied on three locations on apple surface with different curvatures: top, middle and bottom. The second objective was to investigate the temperature variation on the surface of the bruised apples and to examine the capability of visible and thermal imaging in detecting bruised tissues at different times after bruising occurred. Materials and Methods: For these purposes, the experiments were conducted on sixty apples of Golden Delicious variety. From sixty samples, five apples were used for determining apples ripeness index and five apples were used for determining emissivity factor which was used later in calibrating fruit surface temperatures on thermal images. Bruising was simulated by an impact pendulum. Bruising was conducted at three impact energy levels of 200, 700, 1200 mJ and applied at three locations on apple surfaces: top, middle and bottom. The samples affected by bruising-simulated impacting device were kept in a refrigerator at 5°C and were individually imaged in a regular basis until 624 hours after impact application. At the time of imaging, both visible and thermal images were taken from each sample. Samples visible images were taken in an imaging box with uniform controlled lighting. Thermal images were taken while samples were placed in a box that was thermally insulated from surrounding temperature. A newly defined color factor, named excessive yellow index (EYI) was extracted from visible color images. The EYI index formula is EYI = 1.5r+b-1.5g where r, g and b are red, green and blue color values, respectively. Factorial experiment was conducted for the assessment of EYI. This experimental design looked at the effects of three factors of time, impact energy and impact landing location on EYI. Result and discussion: The results showed that time passed after impact and the location of impact application had significant effect on EYI at 95% confidence interval. The apples EYI index decreased until 15 days after impact application and started increasing thereafter. Surface temperatures were extracted from the thermal images of samples. The results of processing thermal images showed that the bruised tissue was cooler than the sound tissue until 48 hours after impact application. Both tissues had the same temperature from 56 to 96 hours and then the bruised tissue started becoming warmer by 0.5-1°C after 96 hours. The color variation of bruised region was not detectable from visible images within the first 48 hours after impact application, while these regions were cooler than undamaged region and detectable from thermal images. The bruised regions started to turn dark brown at 48 hours after impact application. However, there was no temperature difference between bruised and sound regions on fruit surface for the period of 56-96 hours. The bruised brown regions paled after 360 hours. As a result, this reduced the capability of visible images for discriminating bruised apples from sound ones. Conclusion: The results of this research show that both the visible spectrum and thermal imaging systems can record the changes in color and temperature at different times after the bruising in apples. Therefore, these methods can be used as an efficient methods for grading apples.
