Sugars and amino acids were extracted from okara following the
procedures of Giannoccaro et al. (2006) with slight modifications. Five
grams of freeze-dried, defatted okara were extracted with 80 mL of
80% v/v ethanol in a water bath (50 °C, 150 rpm, 30 min). Lactose was
added as an internal standard. Extraction was conducted thrice, and
the combined extracts were concentrated to 10 mL using a rotary
evaporator. One part of concentrated extract was added to 2 parts of
acetonitrile, and the mixture was stored at 4 °C for at least 24 h to
allow complete precipitation of proteins. The precipitate was removed
by centrifugation and the supernatant was stored at−20 °C before use.