Propetries And Structural Features Of The Aggregates During Hydrolyzation Of Soy Protein

Soy protein hydrolysates possess favourable physico-chemical properties such as goodsolubility, dispersibility and stability, it also have some functional properties such asantioxidant activity, antihypertensive effects, cholesterol reduction, non-antigenic andimmunoregulation and so on. So soy peptides have fascinating development prospects.However, an inevitable problem in the hydrolyzation of soy protein is peptides aggregatedduring treatment with proteases. The aggregates are insoluble and reduce the yield of thesoluble product. This paper was to study the aggregation behavior of soy protein hydrolysates,aimed to master the rule of the aggregation and physicochemical properties of the aggregates.The internal structure of the aggregates was further investigated.Soy protein isolates (SPI) are mainly composed of glycinin (11S) and β-conglycinin (7S).In this paper, the aggregation behavior of hydrolysates from SPI,7S and11S with Alcalasewere studied respectively. It was shown that the hydrolysates of11S were mostly apt toaggragation, followed by SPI, while the hydrolasates of7S would not aggregated throughoutthe hydrolyzation.7S and its hydrolysates had an inhibiting effect on aggregating behavior of11S hydrolysates, and a stabilization effect on the structure of aggregates.Then the influence of various hydrolyzation conditions on the aggregation of11Shydrolysates was studied by nephelometry. The results showed as follows.1) Species ofenzymes had an influence on aggregation of11S hydrolysates. Alcalase was most likely tolead to aggregation of11S hydrolysates, followed by papain, and finally were trypsin, pepsin,neutral protease respectively.2) The concentration of11S played an important role in theaggregation. The aggregation was more obvious with higher protein concention.3) The higherthe temperature, the more obvious the aggregation.4) pH had a less impact on aggregation. AtpH8.0,11S hydrolysates aggregated most obviously during hydrolyzation by Alcalase.Subsequently, the proterties of water soluble ingredients and insoluble aggregates of11Shydrolysates were studied. The particle size of the aggregates increased with the DH, and theyield of the aggregates first increased then decreased with the increasing DH. At DH5%, themaximum aggregates were obtained with the yield of about21%. The molecular weight of thewater soluble ingredients was larger than that of water insoluble aggregates. SDS-PAGEshowed that the aggregates were mainly consist of peptides with molecular weight smallerthan6.5kDa. The surface hydrophobicity, the content of hydrophobic amino acids and theweighted retention time in C18column of water soluble ingredients were all lower than thatof water insoluble aggregates. This indicated that the hydrophobic interaction is the maindriving force for the formation of aggregates.At last, the distribution of disulfide-linked peptides in aggregates was investigated. The content of total sulfhydryl decreased with the increasing DH. This might be caused by theoxidation of sulfhydryl to non-disulfide products or the removal of sulfhydryl from Cysteine.The content of total sulfhydryl in water soluble fragments was higher than that of waterinsoluble aggregates determined by4-DPS method. Tricinine-SDS-PAGE labeled with mBBrshowed the molecular weight of peptides that contained sulfhydryls in the aggregates waslower than that of water soluble fragments. With the combination of diagonal electrophoresisand MALDI-TOF/TOF-MS, the results showed that the peptides of aggregates were mainlyfrom basic polypeptide, while the peptides of water soluble fragments were mainly fromacidic polypeptide.