Elsevier

Process Biochemistry

Volume 96, September 2020, Pages 122-130
Process Biochemistry

Molecular size and immunoreactivity of ethanol extracted soybean protein concentrate in comparison with other products

https://doi.org/10.1016/j.procbio.2020.06.007Get rights and content

Highlights

  • This study provides a better understanding of the mechanism of immunoreactivity reduction in soy protein products.

  • The allergen stability of different soybean protein products after pepsin hydrolysis was analyzed.

  • Solubility of most allergenic proteins was higher at pH 12 than at pH 8.2, and the lowest at pH 2.

Abstract

Soy protein products are widely used as high nutrient sources in many food industries. However, allergenic proteins make it as one of the “big 8” foods. The objective was to analyze the molecular size, changes in protein structure and immunoreactivity of ethanol extracted soy protein concentrate in comparison with other major commercial soybean protein products extracted at different pH, and allergen stability after pepsin hydrolysis. The results showed that immunoreactivity of defatted soy white flakes (SPC2) was 227.7 mg IgE/kg protein or 102.4 mg IgE/kg product based on enzyme-linked immunosorbent assay (ELISA), the highest compared with other soy products; soy protein isolate (SPI) was the lowest (76.7 mg IgE/kg protein). Solubility of most allergenic proteins was higher at pH 12 than at pH 8.2, and the lowest at pH 2, especially no ß-conglycinin was extracted at pH 2. These results contribute to the understanding of the mechanism of immunoreactivity reduction in Soycomil and demonstrate competitive advantages compared to other soy protein products.

Introduction

Soybeans play an important role in people's daily diet. They contain 40 % dry matter, and soy protein contains all the essential amino acids in the human body. It is a good source of protein that can match meat and milk. Soybeans also contain several bioactive components such as isoflavones [1,2], Bowman-Birk inhibitor [3], saponins [4,5], lunasin [6,7] that possess estrogenic, antifungal, and antioxidant activities believed to prevent hypercholesterolemia, some types of cancer, diabetes, kidney disease, and osteoporosis [[8], [9], [10], [11]].

Despite all these advantages, the Food Allergen Labeling and Consumer Protection Act of 2004 released soybean is currently one of the “big 8” common allergens, and the occurrence of allergies has made many people unable to benefit [[12], [13], [14], [15]]. The estimated around 0.5 % of the U.S. population is allergic to soy [[16], [17], [18]]. Although soybean contains at least 33 allergenic proteins that bind to immunoglobulin E (IgE) [19], only a few are responsible for most allergic reactions, so identifying these key proteins in soy protein products is important. ß-Conglycinin and glycinin account for about 70 % of the total storage proteins in soybean seeds [20], and are implicated as major allergens [21,22].

Due to the high protein concentration and technological properties (e.g., hydration, Oil absorption, emulsifying, Water retention and flavor binding characteristics) soy protein products are not only widely used in fried food, dairy products, breakfast cereals, puffed food, and dietary foods, but also used as livestock feed. However, the allergenic activity of some soybean proteins extensively limited the application and consumption of soybean protein products. The process that soybean undergoes in order to obtain these products may change its allergenicity. However, there is not much information about the components of allergens and their immunoreactivities in new soy protein products. The objective was to evaluate the molecular size, changes in protein structure and immunoreactivity, using human plasma from subjects allergic to soybean, of ethanol extracted soy protein concentrate in comparison to other major commercial soybean protein products extracted at different pHs, and the stability of allergenic proteins after pepsin digestion.

Section snippets

Materials

ß-Mercaptoethanol (ß-ME), tris buffered saline tablets, deoxycholate, bovine serum albumin (BSA), para-nitrophenyl phosphate (PNPP), tween-20 and Corning™ Sterile syringe filter pore size 0.02 mm were purchased from Sigma–Aldrich™ (Saint Louis, MO,USA). Reagents used for SDS–PAGE included running buffer with Tris/SDS/Gly, Coommassie Blue bio-safe dye, Laemmli blue dye and prestained SDS–PAGE molecular mass broad-range standards were obtained from Biorad (Hercules, CA, USA). Immunoblot PVDF

Soluble protein concentration

Soluble protein concentration of soy products extracted at different pHs are presented in Table 1. The results are expressed as percent of the extracted protein of samples that were initially extracted with buffer pH 8.2 and the remaining solid material was further extracted with either buffer pH 2.0 or pH 12.0. As shown, most results using RC DC, because the Lowry assay modified to be reducing agent compatible, were lower than with the DC, probably due to the existence of some reducing agents.

Conclusions

The results in this study suggest that protein solubility and the immunoreactivities of soybean protein products were different since the manufacture process was different. The immunoreactivities of SPC2 were 227.7 mg IgE/kg protein and 102.4 mg IgE/kg product, the highest compared with the other soy protein products since it was prepared without thermal or ethanol extraction. The immunoreactivity of SPI was the lowest (76.7 IgE/kg protein) if consumed the same amount of protein comparing with

CRediT authorship contribution statement

Huanyu Zheng: Methodology, Investigation, Resources, Writing - review & editing, Funding acquisition. Guosen Yan: Investigation, Writing - original draft, Software. Susan Marquez: Validation, Formal analysis. Stephenia Andler: Data curation. Yueming Dersjant-Li: Resources. Elvira Gonzalez de Mejia: Conceptualization, Methodology.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

We gratefully acknowledge for financial support from Science and Technology Department of Heilongjiang Province (ZD2019C005, 2019ZX08B01), Ministry of Science and Technology of the People’s Republic of China (2013AA102208) and China Scholarship Council.

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