Abstract
Soymilk is one of those remarkable beverages, as well as material for tofu making. It contains almost 4 % protein, which has a good amino acid balance and health benefits. For soymilk making, the first step is commonly imbibition of the soybeans. Removing the imbibition step is expected to show some merits such as a decrease in the risk of microbial growth, cutting down water waste from imbibition and saving imbibition time. So the effect of removing the imbibition step on soymilk making was examined. Namely, non-imbibed soybeans (whole beans) were milled with the necessary amount of water in a blender under various conditions (revolution of blender and milling time) to prepare soymilk with no imbibition. Yield of the soymilks were almost equivalent between non-imbibed and imbibed beans, but solid content was lower in non-imbibed beans at low revolution of the blender. With increasing revolution, solid content increased and finally became almost equivalent to that prepared from imbibed beans. Thus, removing imbibition is thought to have only a slight effect on dispersion of soymilk and to be effective for improving soymilk processing conditions. Soymilk for beverages is quite different from that for tofu making. The soymilk for beverages is produced by milling imbibed or non-imbibed seeds at high temperature. High temperature milling is used to inactivate lipoxygenase, which is known to cause beany flavor. So soymilk prepared by high temperature milling was then characterized to analyze precipitation, denaturation and protein aggregation. For the result, milling at temperatures from 70 to 80 ℃ allowed precipitation and denaturation to increase and accelerate growth of aggregates, but over 80 ℃ , the size of protein aggregates decreased and were more dispersible. In addition to inactivating the lipoxygenase, milling over 80 ℃ was also shown to improve dispersion of soymilk. By replacing water bath heating with a Joule heating device, soymilk is shown to be much more rapidly and exactly heated. Using the Joule heating device, soymilk was prepared with various heating rates. For the results, heating rate affected the quality of soymilk and also tofu curd derived from the soymilk. An increase in heating rate decreased precipitation and viscosity. From the above data, processing conditions, such as imbibition, milling and heating are thought to greatly affect quality of soymilk. Further investigation on processing of soybean is thought to be important in the future.
