Aggregation of soy protein-isoflavone complexes and gel formation induced by glucono-δ-lactone in soymilk.

Sheng-Yang Hsia,Yu-Hsuan Hsiao,Jung-Feng Hsieh,Wen-Tai Li

doi:10.1038/srep35718

Abstract

This study investigated the glucono-δ-lactone (GDL)-induced aggregation of isoflavones and soy proteins in soymilk. High-performance liquid chromatography (HPLC) analysis indicated that isoflavones mixed with β-conglycinin (7S) and glycinin (11S) proteins formed 7S-isoflavone and 11S-isoflavone complexes in soymilk supernatant fraction (SSF). Most of the soy protein-isoflavone complexes then precipitated into the soymilk pellet fraction (SPF) following the addition of 4 mM GDL, whereupon the pH value of the soymilk dropped from 6.6 to 5.9. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and HPLC analysis suggest that the addition of 4 mM GDL induced the aggregation of most 7S (α’, α and β subunits), 11S acidic and 11S basic proteins as well as isoflavones, including most aglycones, including daidzein, glycitein, genistein and a portion of glucosides, including daidzin, glycitin, genistin, malonyldaidzin and malonylgenistin. These results provide an important reference pertaining to the effects of GDL on the aggregation of soy protein-isoflavone complexes and could benefit future research regarding the production of tofu from soymilk.

Highlights

Soymilk can be transformed into gelatinous soybean curd, which is referred to as tofu[10]
An increase in GDL concentration led to a decrease in the quantity of proteins in the soymilk supernatant fraction (SSF) and an increase in the soymilk pellet fraction (SPF)
90.1% of the soymilk proteins were aggregated into SPF following the addition of 4 mM GDL, and the total quantity of proteins increased from 0.12 ± 0.01 to 12.45 ± 0.54 mg/mL

Summary

Introduction

Soymilk can be transformed into gelatinous soybean curd, which is referred to as tofu[10]. One previous study reported that calcium chloride induced the coagulation of β-conglycinin, glycinin and isoflavones in soymilk[16]. The addition of 5 mM calcium chloride induced the coagulation of most of the 7S (α’, αand β), 11S acidic (A1a, A1b, A2, A3 and A4) and 11S basic (B1a) proteins was well as isoflavones, including daidzein and genistein. The results clearly demonstrate that isoflavones (including daidzein and genistein) bind to 7S and 11S to form 7S-isoflavone complexes and 11S-isoflavone complexes in soymilk. These soy protein-isoflavone complexes coagulate into SPF following the addition of calcium chloride. The soymilk proteins are aggregated by GDL, it is unclear how the isoflavones precipitate into the tofu during the production process. The objective of this study was to investigate the GDL-induced aggregation of 7S, 11S and isoflavones in soymilk

Objectives

Methods

Results