Soymilk production is increasing year-on-year due to being perceived as a good way to obtain many important functional dietary components. Indeed, compared to bovine milk, soymilk production is expected to increase in the future. Considering the balance between supply and demand for protein sources, replacing some meat protein with soybean protein by improving the quality of soybean product is considered valuable. Consequently, this review will examine and summarize the progress of research being conducted on soymilk. A knowledge of soymilk requires an understanding of its structure, and numerous approaches have been taken in this regard. Investigations on heating, milling and extraction in soymilk processing are considered essential. Further, investigations on secondary processing of soymilk, such as concentration, membrane treatment, drying, and freezing are also introduced.

Manninotriose is a characteristic trisaccharide contained in fermented soybean foods, and is produced by desorption of one molecule of fructose from stachyose. In this study, we examined the manninotriose content in several kinds of commercially available fermented soybean foods and homemade foods, such as natto, miso, and tempeh, to clarify the factors affecting manninotirose production. The water-soluble fraction was obtained from both purchased or homemade fermented food, and the oligosaccharide contents were measured using high-performance liquid chromatography. We observed difference in manninotriose content among different kinds of fermented soybean food, which suggests that production of manninotriose is dependent on the microorganisms involved in the fermentation. Manninotriose concentration differed among natto, miso and tempeh in decreasing order. This tendency shows that natto has higher production efficiency of manninotriose, defined as the ratio of manninotriose to the initial stachyose content in the molar basis. The time course study of fermentation demonstrated that manninotriose concentration increased with degradation of stachyose, and the concentration of manninotriose was maintained during fermentation and storage. It was suggested that the factors affecting manninotriose production were the difference in stachyose content in the soybeans used as raw materials, the types of microorganisms involved in fermentation, and the conditions of fermentation, such as temperature and salinity.

Ayu-narezushi is a traditional dish from Toyama, Japan that is produced by the fermentation of ayu (Plecoglossus altivelis) with rice-koji. The chemical and microbiological characteristics of ayu-narezushi made with and without koji were investigated to elucidate the effect of koji on fermentation. In both samples during fermentation, lactic acid and free amino acid content increased, and pH, carbohydrates and solid contents decreased. This tendency was more apparent in the samples fermented with koji. In both samples, the number of lactic acid bacteria increased during fermentation, especially in the samples prepared without koji. Throughout the fermentation period, the dominant lactic acid bacteria species in the samples prepared with koji was Lactobacillus sakei. The predominance of L. sakei in the samples prepared without koji gradually decreased during fermentation. It is suggested that the rice-koji used in this study contributed to both the formation of a stable microflora dominated by L. sakei and a pleasant flavor.