EXTRACTION OF OLIGOSACCHARIDES DURING COOKING OF WHOLE SOYBEANS

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Abstract
Raffinose and stachyose present in soybeans have been reported to cause flatulence. The objective of this work was to study the aqueous extraction of whole soybeans during water cooking to determine optimum conditions for maximum removal of oligosaccharides with minimum loss of protein. Chief variables were bean to water ratio (1:3, 1:5, 1:7.5 and 1:10) and pH. Residual oligosaccharides in the soybeans were determined by silylation followed by GLC analysis. During 20 min boiling in water, a 1:10 ratio resulted in 33% oligosaccharide extraction (g per 100g original oligosaccharide) with 1% protein loss (g per 100g original protein) while a 1:3 ratio gave only 7.7% oligosaccharide removal with 0.9% protein loss. When the time was extended to 60 min, a 1:10 ratio resulted in 59% extraction with 2.6% protein loss and 12% total solids loss (g per 100g original soybean solids). With the latter treatment, sucrose fell from 6.5 to 3.0% dry basis and fructose fell from 1.6% to 1.0%. Addition of 0.5% NaHCO3 to the tap water (initial pH 8.1) increased ohgosaccharide removal but trebled protein loss to 6.8% while addition of HCI to initial pH 4.3 gave about the same protein loss and oligosaccharide removal as tap water.