Integrated Metabolomics and Volatolomics for Comparative Evaluation of Fermented Soy Products.

Sang-Hee Lee,Digar Singh,Hae-Jin Kim,Sunmin Lee,Choong-Hwan Lee,Seung-Hwa Lee

doi:10.3390/foods10112516

Abstract

Though varying metabolomes are believed to influence distinctive characteristics of different soy foods, an in-depth, comprehensive analysis of both soluble and volatile metabolites is largely unreported. The metabolite profiles of different soy products, including cheonggukjang, meju, doenjang, and raw soybean, were characterized using LC-MS (liquid chromatography–mass spectrometry), GC-MS (gas chromatography–mass spectrometry), and headspace solid-phase microextraction (HS-SPME) GC-MS. Principal component analysis (PCA) showed that the datasets for the cheonggukjang, meju, and doenjang extracts were distinguished from the non-fermented soybean across PC1, while those for cheonggukjang and doenjang were separated across PC2. Volatile organic compound (VOC) profiles were clearly distinct among doenjang and soybean, cheonggukjang, and meju samples. Notably, the relative contents of the isoflavone glycosides and DDMP (2,3-dihydro-2,5-dihydroxy-6-methyl-4H-pyran-4-one) conjugated soyasaponins were higher in soybean and cheonggukjang, compared to doenjang, while the isoflavone aglycones, non-DDMP conjugated soyasaponins, and amino acids were significantly higher in doenjang. Most VOCs, including the sulfur containing compounds aldehydes, esters, and furans, were relatively abundant in doenjang. However, pyrazines, 3-methylbutanoic acid, maltol, and methoxyphenol were higher in cheonggukjang, which contributed to the characteristic aroma of soy foods. We believe that this study provides the fundamental insights on soy food metabolomes, which determine their nutritional, functional, organoleptic, and aroma characteristics.

Highlights

Fermentation is a metabolic bioprocess that causes biochemical changes in the organic substrate, through the action of microbial enzymes [1]
Methoxyamine hydrochloride, pyridine, potassium persulfate, N-methyl-N-(trimethylsilyl) trifluoroacetamide (MSTFA), 2,2 -azino-bis (3ethylbenzothiazoline-6-sulfonic acid), diammonium salt (ABTS), 6-hydroxy-2,5,7,8tetramethylchromane-2-carboxylic acid (Trolox), sodium acetate, acetic acid, 2,4,6-Tris (2-pyridyl)-s-triazine (TPTZ), hydrochloric acid (HCl), iron (III) chloride hexahydrate, sodium carbonate, Folin–Ciocalteu’s phenol, sodium hydroxide, gallic acid, and naringin were obtained from Sigma-Aldrich
Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) models, obtained from GC–TOF-MS analysis, displayed cheonggukjang, meju, and doenjang extracts that were clearly segregated from the unfermented soybean samples across PC1, which suggests their varying metabolite profiles, according to different fermentative bioprocesses

Summary

Introduction

Fermentation is a metabolic bioprocess that causes biochemical changes in the organic substrate, through the action of microbial enzymes [1]. Fermentation is considered a customarily important method of food processing, as it adds superior taste, flavor, and nutrition to the end-product, as well as enhanced shelf life, compared to raw materials [2]. Depending on the fermentation process, various fermented foods are produced, such as cheonggukjang (fermented soybean), meju (fermented soybean block), doenjang (fermented soybean paste), ganjang (fermented soy sauce), and gochujang (fermented hotpepper paste) [4]. The cheonggukjang, prepared traditionally, is made by steaming soybeans for several days with rice straw, and meju is made from boiled beans, wrapped in rice straw and fermented for several months. Doenjang is made by fermenting the meju for an extended duration, ranging 3 months to 3 years, and separating the liquid layer as ganjang (Figure 1) [5].

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Conclusion