30C-29 |
Study of the behavior of soy protein isolate when submitted to heat treatment and to treatment with maleic anhydride, and the effects of these treatments on enzyme hydrolysis by a-chymotrypsin |
A. S. Souza, V. S. Nunes Silva, F. M. NETTO, and J. Amaya-Farfán. Departamento de Planejamento Alimentar e Nutrição, Universidade Estadual de Campinas, Faculdade de Engenharia de Alimentos, C.P. 6121, Campinas-S.P., 13083-970, Brazil The potential of soybeans for direct feeding or as a source of functional ingredients increased considerably throughout the last decade. Hydrolysates also play an important role in the composition of formulations for specific ends and also in the nutritional enrichment of foods. The objective of this study was to evaluate the behavior of soy protein isolate (SPI) when submitted to heat or to a chemical treatment with maleic anhydride (MA), and the effects of these treatments on hydrolysis by a-chymotrypsin. The native soy protein isolate (SPIn), produced in the laboratory, was submitted to heat treatments at 70 (IPS70) and 80°C (IPS80) for 10', and to chemical treatment with 0.1535M MA (IPSM). Hydrolysis was monitored using pH-Stat to obtain 4.5% of DH. The trypsin inhibitors in the isolates were quantified using BAPNA as substrate. The protein profiles of the isolates and hydrolysates were analyzed using SDS-PAGE and RP-HPLC. The levels of inhibitor were 81.40; 51.80; 41.70 and 45.26 UTI/mg protein for IPS; IPS70; IPS80 and IPSM respectively. The electrophoretic profiles of the SPIn and the heat-treated isolates showed no differences in the relative proportions of the 7S and 11S fractions, although when compared to IPSM, differences in the sub-units were found. The chromatographic profiles of the isolates showed great differences in the hydrophobic nature of the isolates. The susceptibility of the 7S and 11S fractions to hydrolysis was greater in the hydrolysates treated at 80°C and with MA. The hydrolysates showed different profiles with respect to MW and the hydrophobic nature of the peptides, although presenting the same DH. The results suggest that the characteristics of the hydrolysates were dependent on the treatment previously suffered by the protein, and not exclusively on the DH, and that the hydrolysates could show differentiated functional characteristics. Project partially financed by FAPESP (proc. 9812980-8)
Session 30C, Food Chemistry: Proteins
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