Abstract
Soymilk is lower in calories compared to cow’s milk, since it is derived from a plant source (no cholesterol) and is an excellent source of protein. Despite the beneficial factors, soymilk is considered as one of the most controversial foods in the world. It contains serine protease inhibitors which lower its nutritional value and digestibility. Processing techniques for the elimination of trypsin inhibitors and lipoxygenase, which have shorter processing time and lower production costs are required for the large-scale manufacturing of soymilk. In this study, the suitable conditions of time and temperature are optimized during microwave processing to obtain soymilk with maximum digestibility with inactivation of trypsin inhibitors, in comparison to the conventional thermal treatment. The microwave processing conditions at a frequency of 2.45 GHz and temperatures of 70 °C, 85 °C and 100 °C for 2, 5 and 8 min were investigated and were compared to conventional thermal treatments at the same temperature for 10, 20 and 30 min. Response surface methodology is used to design and optimize the experimental conditions. Thermal processing was able to increase digestibility by 7% (microwave) and 11% (conventional) compared to control, while trypsin inhibitor activity reduced to 1% in microwave processing and 3% in conventional thermal treatment when compared to 10% in raw soybean.
Highlights
Soymilk is a high protein liquid with considerable amounts of carbohydrates, fats, essential vitamins and mineral, generally produced by grinding soaked soybeans in excess water, which is filtered to separate out the milk from solids and fiber
This study reports the effect of microwave processing on the reduction of trypsin inhibition activity (TIA) in comparison to the conventional thermal processing of soymilk
In the case of microwave processing, from the values of parameter estimates or regression coefficients it was concluded that the most influential factor affecting the In vitro Protein digestibility (IVPD) is the temperature with the highest regression coefficient of 1.694, followed by a square term of time, 1.250, a linear term of time, 0.3519, and lastly the interactive term of temperature and time with −0.620 regression coefficient
Summary
Soymilk is a high protein liquid with considerable amounts of carbohydrates, fats, essential vitamins and mineral, generally produced by grinding soaked soybeans in excess water, which is filtered to separate out the milk from solids and fiber. It is a stable oil in water emulsion, where the continuous phase is formed by dispersed soybean protein. Water, 3% protein, 1.5% fat and 1.5% of carbohydrates It contains 7.36 and 0.33 mg/100 mL of riboflavin and thiamin, respectively, a composition similar to cow’s milk but with little-saturated fat and no cholesterol [1,2,3]. The nutritional profile of soymilk and cow’s milk (3.25% milkfat) are summarized in Table 1 [4].
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