Secondary Structure and Subunit Composition of Soy Protein In Vitro Digested by Pepsin and Its Relation with Digestibility.

Yong Yang,Yang Li,Lianzhou Jiang,Zhongjiang Wang,Baokun Qi,Rui Wang,Feifei Han,Xiaonan Sui

doi:10.1155/2016/5498639

Abstract

In the present study, in vitro digestibility and structure of soybean protein isolates (SPIs) prepared from five soybean varieties were investigated in simulated gastric fluid (SGF), using FT-IR microspectroscopy and SDS-PAGE. The result indicated that β-conformations were prone to be hydrolyzed by pepsin preferentially and transformed to unordered structure during in vitro digestion, followed by the digestion of α-helix and unordered structure. A negative linear correlation coefficient was found between the β-conformation contents of five SPIs and their in vitro digestibility values. The intensities of the protein bands corresponding to 7S and 11S fractions were decreased and many peptide bands appeared at 11~15 kDa during enzymatic hydrolysis. β-conglycinin was poorly hydrolyzed with pepsin, especially the β-7S subunit. On the other hand, basic polypeptides of glycinin degraded slower than acidic polypeptides and represented a large proportion of the residual protein after digestion. 11S-A3 of all SPIs disappeared after 1 h digestion. Moreover, a significant negative linear correlation coefficient (r = −0.89) was found between the β-7S contents of five SPIs and their in vitro digestibility values. These results are useful for further studies of the functional properties and bioactive properties of these varieties and laid theoretical foundations for the development of the specific functional soy protein isolate.

Highlights

Soybean protein isolate (SPI) is the main by-product of producing soybean oils, which have been widely used in many protein-based food formulations because of their excellent nutritional and functional properties, availability, and low cost [1,2,3].In the past few years, there has been an increasing interest in the structural design of food-based delivery systems to encapsulate, protect, and release bioactive components believed to benefit human health [4]
Wang et al [16] reported that hemp (Cannabis sativa L.) protein constituents of edestin were rapidly digested by pepsin, to release oligopeptides with molecular weight (MW) less than 10.0 kDa and suggested that the in vitro digestibility of HPIs was comparable to that of SPI
It should be noted that when 2 h digestion was introduced, SPI-A obtained the highest Degree of Hydrolysis (DH) values (8.75), followed by SPI-D (7.37), SPI-E (7.33), SPI-B (7.28), and SPI-C (6.90)

Summary

Introduction

Soybean protein isolate (SPI) is the main by-product of producing soybean oils, which have been widely used in many protein-based food formulations because of their excellent nutritional and functional properties, availability, and low cost [1,2,3].In the past few years, there has been an increasing interest in the structural design of food-based delivery systems to encapsulate, protect, and release bioactive components believed to benefit human health [4]. Soybean protein isolate (SPI) is the main by-product of producing soybean oils, which have been widely used in many protein-based food formulations because of their excellent nutritional and functional properties, availability, and low cost [1,2,3]. Increasing evidences suggest that (1) the structural properties of proteins in plant foods have a major role in resistance to denaturation [10, 11] and (2) plant proteins manifest stability upon gastrointestinal digestion [12, 13]. Wang et al [16] reported that hemp (Cannabis sativa L.) protein constituents of edestin were rapidly digested by pepsin, to release oligopeptides with molecular weight (MW) less than 10.0 kDa and suggested that the in vitro digestibility of HPIs was comparable to that of SPI. Sze-Tao and Sathe [17] suggested that pepsin hydrolysis of almond

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Discussion

Conclusion