Effect of fermented rice culture on the microbiological, biochemical and sensory characteristics of low-salt douchi, a traditional Chinese fermented soybean condiment

Untargeted metabolomics analysis of non-volatile metabolites and dynamic changes of antioxidant capacity in Douchi with edible mushroom by-products

This study investigated the non-volatile metabolites and antioxidant activity of Douchi, an edible mushroom by-product. A total of 695 non-volatile metabolites were detected using UPLC-MS/MS-based metabolomics analysis, and the greatest impact on metabolite composition was observed during Koji-making and the first 5 days of post-fermentation. Throughout the fermentation process, 366 differential metabolites were identified, with flavonoids being the most prominent followed by amino acids and their derivatives, which were found to be important for the quality of edible mushroom by-product Douchi (EMD). The antioxidant capacity of EMD significantly increased with the longer fermentation time, which might be associated with the conversion of isoflavone glycosides to aglycones, amino acids and their derivatives, free fatty acids, group A saponins, and phenolic acids. These findings suggested that different fermentation phases of EMD significantly affected the non-volatile metabolite profile and antioxidant capacity.

Microbiology of fermented soy foods in Asia: Can we learn lessons for production of plant cheese analogues?

The food industry is facing the challenge of creating innovative, nutritious, and flavored plant-based products, due to consumer's increasing demand for the health and environmental sustainability. Fermentation as a unique and effective tool plays an important role in the innovation of food products. Traditional fermented soy foods are popular in many Asian and African countries as nutritious, digestible and flavorful daily staples or condiments. They are produced by specific microorganisms with the unique fermentation process in which microorganisms convert the ingredients of whole soybean or soybean curd to flavorful and functional molecules. This review provides an overview on traditional fermented food produced from soy, including douchi, natto, tempeh, and sufu as well as stinky tofu, including the background of these products, the manufacturing process, and the microbial diversity involved in fermentation procedures as well as flavor volatiles that were identified in the final products. The contribution of microbes to the quality of these five fermented soy foods is discussed, with the comparison to the role of cheese ripening microorganisms in cheese flavor formation. This communication aims to summarize the microbiology of fermented soy foods in Asia, evoking innovative ideas for the development of new plant-based fermented foods especially plant-based cheese analogues.

Characterization of the Key Aroma-Active Compounds in Yongchuan Douchi (Fermented Soybean) by Application of the Sensomics Approach

Yongchuan douchi is a traditional fermented soya bean product which is popular in Chinese dishes due to its unique flavor. In this study, the key aroma-active compounds of Yongchuan douchi were characterized by the combined gas chromatography-olfactometry (GC-O) and gas chromatography-mass spectrometry (GC-MS) with sensory evaluation. In total, 49 aroma compounds were sniffed and identified, and 20 of them with high flavor dilution factors (FD) and odor activity values (OAVs) greater than one were screened by applied aroma extract dilution analysis (AEDA) and quantitated analysis. Finally, aroma recombination and omission experiments were performed and 10 aroma-active compounds were thought to have contributed significantly including 2,3-butanedione (butter, cheese), dimethyl trisulfide (garlic-like), acetic acid (pungent sour), acetylpyrazine (popcorn-like), 3-methylvaleric acid (sweaty), 4-methylvaleric acid (sweaty), 2-mehoxyphenol (smoky), maltol (caramel), γ-nonanolactone (coconut-like), eugenol (woody) and phenylacetic acid (flora). In addition, sensory evaluation showed that the flavor profile of Yongchuan douchi mainly consisted of sauce-like, sour, nutty, smoky, caramel and fruity notes.