Statistical and kinetic studies of the changes in soybean quality during storage as related to soymilk and tofu making.

The objective of this study was to develop statistical equations and kinetic models to describe the changes of soybean quality during storage. Significant correlations (P < 0.0001) were found among most of quality attributes including color parameters (Hunter L, a, b, and DeltaE), solid extractability (as expressed by soymilk solids content), soymilk pH and protein content, tofu yield, hardness, and protein content. Regressed linear equations were developed between color indices (L/L(0), DeltaE) and soymilk/tofu making properties. Empirical equations were developed to relate soybean color indices (L/L(0), DeltaE) and storage conditions including variables of initial moisture content (MC), relative humidity (RH), temperature (T), and duration (t). Kinetics of the changes in soybean color and extractability during storage at 70% RH and 22 to 40 degrees C were investigated. The kinetics was well described by zero-order kinetics. The Arrhenius equation adequately described the temperature dependence of the reaction rate constants for all parameters, from which the activation energies and rate constant were obtained. The equations developed in this study provided simple methods to monitor soybean quality and predict quality changes of soybeans during storage at various conditions.