Soy glycinin, the major globulin of soy protein, has on average 2 sulfhydryls (�SH) and 18-20 disulfide bonds (S-S) per hexamer. The paper investigated the changes of sulfhydryls and disulfide bonds during the hydrolysis process of soy glycinin with Alcalase. �SH and S-S were determined by the Ellman's method and also detected by SEC-HPLC with fluorescent labeling by monobromobimane (mBBr). The results showed that the content of �SH was first increased then gradually decreased during the hydrolysis. �SH and S-S were shown to be concentrated in peptides with low molecular weight (MW). The hydrolysis conditions including temperature and pH had no obvious effects on contents of �SH and S-S, but they could affect their distribution. With the temperature increasing, -SH in MW > 10000 peptides and S-S in MW > 5000 peptides were gradually decreased, while -SH in MW  5000 peptides was gradually shifted into smaller-MW fractions. S-S in MW >1000 peptides was increased and MW <1000 was gradually decreased. The results here, as a preliminary study to screen �SH and S-S, could serve as a theoretical guide not only to elucidate the molecular changes during soy glycinin hydrolysis but also to enrich bioactive peptides containing cystein from the hydrolysates.

Distributions of sulfhydryl groups and disulfides in different molecular weight peptides hydrolyzed from soy glycinin by Alcalase

244th National Meeting (2012)

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