Naturally Fermented Acid Slurry of Soy Whey: High-Throughput Sequencing-Based Characterization of Microbial Flora and Mechanism of Tofu Coagulation.

Yunhe Xu,Qing Ye,Huajiang Zhang,Yang Yu,Zhen Zhang,Lili Zhang,Xiaona Li

doi:10.3389/fmicb.2019.01088

Abstract

Tofu processing generates large quantities of whey as waste water. Although naturally fermented whey serves as a coagulant, the critical constituents remain unknown. High-throughput sequencing identified predominant Lactobacillus in the naturally fermented acid slurry. Lactobacillus casei YQ336 with high coagulating ability and lactic acid production was isolated and its soy protein coagulating mechanism was determined. The acid in YQ336 fermented acid slurry lowered soy milk pH and reduced negatively charged groups of denatured soy protein, leading to coagulation. Acid slurry metal ions also promoted pH decline; moreover, YQ336-produced protease might partially hydrolyse soy protein, further promoting coagulation. Thus, organic acids, metal ions, and enzymes together promote coagulation, with the former acting as the main contributing factor. This study will pave the way for future industrial application of L. casei YQ336 in acid slurry tofu processing and food manufacturing, thereby potentially reducing resource waste and environmental pollution.

Highlights

Tofu, a traditional Chinese food known as soy curd, constitutes an excellent source of plant protein that is rich in beneficial lipids, vitamins, minerals, and other bioactive compounds including isoflavones and soyasaponin
The use of fermented tofu whey in tofu processing avoids the environmental pollution caused by tofu whey emissions and serves as a tofu coagulant to avoid the addition of chemical coagulants, such as calcium sulfate or chloride, being conducive to the production of greener and safer tofu products
Soy whey comprises a good culture medium for growth of various bacteria (Yu et al, 2015), with the microorganisms in the resulting acid slurry directly related to its quality and tofu coagulation ability (Qiao et al, 2010; Fei et al, 2018)

Summary

Introduction

A traditional Chinese food known as soy curd, constitutes an excellent source of plant protein that is rich in beneficial lipids, vitamins, minerals, and other bioactive compounds including isoflavones and soyasaponin. The abundant nutritious and functional factors in tofu whey, such as soluble proteins, lipids, soluble sugar, vitamins, minerals, oligosaccharides, isoflavone, and saponin, support the growth of numerous microorganisms, causing serious environmental pollution (Masangkay, 2012; Corzo-martínez et al, 2016; Li et al, 2017). The acid slurry produced by tofu whey naturally fermented by its. Acid Slurry Tofu Coagulation Mechanism normal micro biota has been used as a traditional tofu coagulant for 400 years in China (Qiao et al, 2010; Fei et al, 2018; Zhang et al, 2018). The use of fermented tofu whey in tofu processing avoids the environmental pollution caused by tofu whey emissions and serves as a tofu coagulant to avoid the addition of chemical coagulants, such as calcium sulfate or chloride, being conducive to the production of greener and safer tofu products

Methods

Results

Conclusion