Chemical characteristics of low-fat soymilk prepared by low-speed centrifugal fractionation of the raw soymilk.

Large oil-protein particles (2 to 60 microm) were found in raw soymilk (or water extract of soybean), which was prepared in specific conditions. The large particles could be separated by sedimentation by centrifuging raw soymilk for 5 to 30 min at a low gravitational force ranging from 96 to 2410 x g. Chemical analysis showed that 80% to 90% of the total lipids and 30% to 40% of the total proteins were located in the precipitated fraction. The supernatant fraction had a dramatically higher protein-to-lipid ratio than the whole soymilk. The ratio of 11S/7S proteins and the ratio of 11S acidic/basic subunits were significantly (P < 0.05) higher in the precipitate than that either in the whole soymilk or in the supernatant. Besides centrifuging conditions, other factors, including soymilk concentration, grinding method, soybean variety, and soybean storage, also significantly (P < 0.05) affected the centrifugal fractionation. This study showed that low-speed centrifugation facilitated the separation of oil-protein particles from raw soymilk, and can be used as an innovative method for preparing low-fat soymilk and 11S protein-enriched ingredients. The findings also increased our understanding of the association or aggregation between proteins and lipids in raw soymilk after grinding.