Secondary Structure and Subunit Composition of Soy Protein In Vitro Digested by Pepsin and Its Relation with Digestibility.
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.
Key Laboratory of Processing Agricultural Products of Heilongjiang Province, College of Food and Bioengineering, Qiqihar University, Qiqihar, Heilongjiang 161006, China; College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Yong
Y
Yang
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Zhongjiang
Z
Wang
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Rui
R
Wang
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Xiaonan
X
Sui
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Baokun
B
Qi
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Feifei
F
Han
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Yang
Y
Li
College of Food Science, Northeast Agricultural University, Harbin, Heilongjiang 150030, China.
Lianzhou
L
Jiang
D005916:Globulins / Q000737:chemistry; D006868:Hydrolysis; D010434:Pepsin A / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry; D017433:Protein Structure, Secondary; D021122:Protein Subunits / Q000737:chemistry*; D030262:Soybean Proteins / Q000737:chemistry*
D005916:Globulins; D010455:Peptides; D021122:Protein Subunits; D030262:Soybean Proteins; C011474:glycinin; D010434:Pepsin A