Food Technology
Fatemeh Shokrollahi; Fakhri Shahidi; Mohammad Javad Varidi; Arash Koocheki; Farshad Sohbatzadeh
Abstract
IntroductionSorghum is a valuable source of starch for human use, being a drought-tolerant cereal grain that contains a large amount of starch (approximately 70%). However, native sorghum starch has limited application in the food industry due to its poor functional properties. Modification of sorghum ...
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IntroductionSorghum is a valuable source of starch for human use, being a drought-tolerant cereal grain that contains a large amount of starch (approximately 70%). However, native sorghum starch has limited application in the food industry due to its poor functional properties. Modification of sorghum starch would overcome its shortcomings and tailor it to the targeted application. Among physical methods, non-thermal plasma is a novel method for starch modifications. Plasma is an ionized gas including electrons, atoms, ions, radicals, and quanta of electromagnetic radiation that affects the functional properties of starch. The effect of plasma on starch is influenced by apparatus type, treatment conditions (feed gas, time, and power), and the source of starch. Two main mechanisms of starch modification are known as cross-linking and oxidation together with depolymerization. Although the effect of plasma on many types of starch has been investigated, no research has yet been found on sorghum starch modification by non-thermal plasma. So, this investigation determines the effects of non-thermal plasma on sorghum starch to overcome the deficiency of the native form and to explore wider applications for sorghum starch. Materials and Methods Sorghum starch was extracted by alkaline steeping and purified using toluene-salt-water treatment. Dielectric Barrier Discharge (DBD) plasma was performed to modify sorghum starch. The applied DBD plasma setup consisted of two flat rectangular aluminum electrodes with the dimension of 6.5×45 cm and 7×18 cm and an electrode distance of 3 and 6 mm for air and argon plasma, respectively. Each of the electrodes was covered with a mica sheet as a dielectric barrier. DBD reactor was supplied with alternating current (AC). The frequency was adjusted to 375 Hz. Starch samples were treated for 1, 10, and 20 min at 23 kV at atmospheric pressure. The amylose content of sorghum starch was determined by iodine binding colorimetry. Evaluation of other chemical parameters including protein, lipid, ash, and moisture was carried out according to AAC methods. The clarity was determined using a spectrophotometer at 650 nm. The swelling and solubility of 1.5% sorghum starch suspension (at 55, 65, 75, and 85 °C) were measured using the centrifuge method. The centrifuge-filtration method was performed to evaluate freeze-thaw stability of sorghum starches up to 4 cycles. Results and Discussion Chemical parameters showed that the extracted sorghum starch was purified. The amount of protein, lipid, ash, and amylose was 0.39, 0.15, 0.59, and 29.23%, respectively. Plasma caused significant altering in sorghum starch properties. Compared to the argon plasma, the air plasma was more effective at increasing the clarity, solubility, and freeze-thaw stability. Increasing the time of treatment also improved the above-mentioned functional properties. The clarity of native starch (14.02%) was increased to 56.10% for the sample treated with air plasma for 20 min, probably due to intense oxidation and depolymerization of starch molecules. While the lowest clarity (13.07%) belonged to the 1-min argon plasma treated sample, this value was improved with increasing time of treatment. Probably cross-linked bonds were predominantly formed during the first minute of argon plasma treatment, resulting in a reduction of paste clarity, while a competitive depolymerization and oxidation reaction could be a reason for the increase of paste clarity. Solubility was increased for all treatments (except for argon-1 min). The highest solubility in each of the temperatures was found for 20 min air plasma treated sample. Depolymerization of starch molecules under plasma treatment produces low molecular weight fragments which leach out easily and increase solubility. The swelling power of 20 min air plasma treated starch was lower than that of native starch, probably due to the structural disintegration. Other samples had higher swelling power. The lower freeze-thaw stability of 1 and 10 min argon plasma treated samples may be due to cross-linking which increase retrogradation. The 20 min air-plasma treated sample had higher stability than other samples in 3 and 4th cycles of freeze-thawing. The freeze-thawing stability of other samples was similar to that of the native starch. Conclusion Non-thermal plasma treatment improved the functional properties of sorghum starch. The best results were detected for the sample treated with air plasma for 20 min. Cross-linking may be the main reaction in the first minute of argon-plasma treatment. However, this mechanism was suppressed in a longer treatment time. It may also be stated that the effect of oxidation along with depolymerization was predominant in air-plasma treatment.
Food Technology
Samira Farizad; Hajar Abbasi
Abstract
Introduction
Hydrocolloid is a term refers to all polysaccharides extracted from plants, seeds, and microbial sources that regardless of their biological and nutritional role has various functional properties in food products such as concentration and gel production of aqueous solutions, stabilization ...
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Introduction
Hydrocolloid is a term refers to all polysaccharides extracted from plants, seeds, and microbial sources that regardless of their biological and nutritional role has various functional properties in food products such as concentration and gel production of aqueous solutions, stabilization of foam, emulsions and dispersed systems, prevention of ice and sugar crystals, control of the release of flavor compounds and consequently control and improve food quality. Ultrasound has been widely used in the food industry due to its numerous physical and chemical effects. The effect of ultrasound is due to cavitation, heating, dynamic mobility and shear stresses to the sample. Today, ultrasound is used as a green new technology with unique effects on food storage and processing. One of the newest applications of ultrasound is altering the structure of polymers such as polysaccharides. Changes in the structure of hydrocolloids lead to modification in their functional properties.
Materials and Methods
In this study, effect of ultrasonic waves, time (0-90 min) and processing temperature (25-75 °C) on physicochemical, rheological and functional properties of locust bean gum was investigated. In this regards, different parameters including changes in pH, solubility, minimum gelatinization concentration, viscosity and emulsifying properties (Emulsifying capacity, emulsion stability and particle dimensions) of treated locust bean gum were determined. Response surface methodology in central composite design was used to evaluate the effect of independent variables on qualitative properties of locust bean gum and model their changes. The best treatment condition was determined and the optimum treated samples were evaluated and compared in microstructure using scanning electron microscopy, rheological properties (rotational and oscillatory test) and Fourier transform infra-red.
Results and Discussion
The results showed that with increasing the time of ultrasound treatment, pH, and viscosity of the hydrocolloid decreased and its solubility and minimum gel concentration increased. However, with increasing temperature, pH, minimum gelatinization concentration and hydrocolloid viscosity increased and its solubility decreased. Optimization of treatment conditions was performed by considering the achievement of the best hydrocolloid performance characteristics. Two different temperature and time conditions were proposed for the desirable treatment of the hydrocolloid using ultrasound. In the first case, the selection criteria were to achieve the best solubility and emulsifying properties of the hydrocolloid, and in the second case, the selection criteria were solubility and emulsifying properties improvement while maintaining the gelatinization properties of the hydrocolloid. Based on the desired quality factors, optimization was performed and the results showed that in the first optimal sample (treated at 40 ° C and 48.9 minutes), solubility and emulsifying properties and in the second optimal sample (treated at 66.67 ° C and 15 Min) by maintaining the gelation properties of hydrocolloid, the solubility of the hydrocolloid increased significantly. The performance of treated samples validated developed models. SEM results showed that the ultrasound increased three-dimensional structure of gum. The smaller microscopic structure was observed in untreated sample and the larger one was in treated with ultrasonic waves for 40.9 minutes at 40 ° C. Therefore, ultrasound caused agglomeration of treated freeze dried gum. It is noteworthy that several holes observed in the structure of treated gum with ultrasonic, which can increase solubility of the gum. The flow behavior of the sonicated and control samples showed that the viscosity of all samples decreased with increasing shear rate, which indicates their pseudoplastic behavior. At low shear rates (about 0.01 per second), the viscosity of the control sample was higher than that of the sonicated samples. However, at high shear rates (about 40 per second), viscosity of the three samples were almost the same. Therefore, the control sample was more affective to shear rate compared to the treated samples. The modulus of elasticity (G ') and viscosity (G' ') of the treated specimens were lower compared to the control. Also, the frequency sweep of samples shown that in the frequency range under study, G 'and G'' were frequency dependent and with increasing frequency, the amount of these two parameters increased. This observation indicates the influence of rheological properties of the samples on the frequency changes that are commonly observed in suspensions. At low frequencies, the predominance of viscous behavior over elastic was observed in all three control and ultrasonic samples (G ''> G ') and this feature was higher in the treated samples than the control. The modulus of elasticity and viscosity of the treated sample for 49 minutes was lower than other treated samples for 15 minutes, which shows the effect of ultrasound on the rheological properties of the hydrocolloid.
Conclusion
The results of this study showed that ultrasonic waves provide a good opportunity to change the physical and functional properties of carob seed gum. It is possible to significantly improve the solubility and emulsifying activity of this hydrocolloid using ultrasound. It is necessary to determine the treatment conditions of the sample according to the intended application.
Food Engineering
Saeid Nejatdarabi; Mohebbat Mohebbi
Abstract
In this study the effect of drying conditions on physical and rehydration properties of foam-mat dried mushroom powder was investigated. Physical properties included moisture content, aw, hygroscopicity, particle size, flowability and cohesiveness, angle of repose, and Tg. The results showed physical ...
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In this study the effect of drying conditions on physical and rehydration properties of foam-mat dried mushroom powder was investigated. Physical properties included moisture content, aw, hygroscopicity, particle size, flowability and cohesiveness, angle of repose, and Tg. The results showed physical properties of mushroom powder significantly (p<0.05) affected by dry temperature. The water activity of mushroom powder was below 0.3, which leads to stable conditions. As decreasing drying temperature, the particle size of mushroom powder increased and led to the increase moisture content and aw. The mushroom powder showed better flowability as increased drying temperature. Tg of mushroom powder ranged from 41.3- 55.6°C. An increase in drying temperature led to increasing wettability and dispersibility. The drying condition had no-significant effect (P<0.05) on the solubility of mushroom powder.
