Thermal treatment for soybean flour processing with high-quality color and reduced Kunitz trypsin inhibitor

Abstract

In this work thermal treatment was applied in whole soybean flour and bleached whole soybean flour production aimed at Kunitz trypsin inhibitor (KTI) reduction and color. A 22 Central Composite Rotational Design was developed to evaluate the effects of temperature (91.80–148.20 °C) and time (15.9–44.10 min). In general, the bleached whole soybean flour presented higher KTI reduction and better color than whole soybean flour in the evaluated temperature and time ranges. It was observed that at 148.2 °C for 30 min the whole soybean flour presented a lower KTI value (1.56 mg/g) than bleached whole soybean flour (1.48 mg/g) and good luminosity. As the bleached presents an extra step in the treatment process, new experiments were made with whole soybean flour without bleached to evaluate KTI and color reduction as a time function (10–30 min) at 148.2 °C. The time was evaluated the verify the behavior of KTI and color of whole soybean flour. The treatment at 148.2 °C for 20 and 30 min presented the lowest KTI values, however, the L* color value at 20 min was higher and soybean flour was whiter, hence 20 min was considered the best condition for whole soybean flour production. Practical applications: In order to increase the nutritional quality of soybeans and use them as food, the inactivation of protease inhibitors is required. As soybean nutritional value is adversely affected by protease inhibitors presence that are considered anti-nutritional factors, these need to be eliminated. Thermal treatment has been used as a physical method to inactivate these factors. However, it must be controlled to avoid essential amino acids destruction. Thermal treatment prior to soybean processing for flour production is common. However, recommendation for the best time and temperature for the grains is nonexistent in order to inactivate and/or reduce their phytochemicals with anti-nutritional action, to the detriment of those with functional effect, preserving their nutrients. Usually, commercial soybean products are thermally treated with less than 20% of in natura soybean trypsin inhibitory activity.