59D-20 |
Hydrophobicity of bitter peptides from soy protein hydrolysates |
A. D. CLARKE, M. Cho, N. Unklesbay, and F. H. Hsieh. Dept. of Food Science, Univ. of Missouri, Columbia, 256 Eckles Hall - Stringer Wing, Columbia, MO 65211 Proteolytic enzyme treatment of soy protein is carried out for improving chemical, functional and nutritional properties, but it may result in off-flavor. Bitterness is an objectionable character that is a major limitation in utilizing protein hydrolysates in food and beverage applications. The average free energy for the transfer of the amino acid side chains from ethanol to water (Q value) has been proposed as an important predictor of peptide bitterness. The objective was to characterize the bitterness and hydrophobicity of peptides from commercial soy protein hydrolysates for purposes of selectively removing bitter peptides or predicting degree of bitterness. Five peptide fractions from two commercial soy protein hydrolysates were recovered by ultrafiltration through four molecular weight cut-off (MWCO) membranes (1 kDa, 3 kDa, 5 kDa, and 10 kDa). Freeze-dried fractions were evaluated for relative bitterness expressed as caffeine equivalents, molecular weight distribution by HPLC, amino acid composition by standard hydrolysis methods, and hydrophobicity based on amino acid composition. The bitterness of soy peptides was related to molecular mass with maximum bitterness observed at approximately 4 kDa for one hydrolysate and 2 kDa for the other. Bitterness did not have significant correlation (P> 0.05) with hydrophobicity based on Q value calculated from amino acid composition and the transfer of free energy of individual amino acids. Bitterness of fractionated peptides was significantly associated with medium molecular mass (1-4 kDa) and small peptides (<1 kDa) were much less bitter. Fractionation through selected MWCO membranes revealed that separation of bitter peptides could be achieved with ultrafiltration. The hydrophobicity based on Q value did not correlate with bitterness; therefore, it is not useful for predicting bitterness of soy protein hydrolysates.
Session 59D, Food Chemistry: Proteins and Physicochemical Properties
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