Antioxidant Activity and Contents of Total Phenolic, Monacolin K, GABA and Citrinin of <i>Monascus</i>-Fermented Soy Sauce

The fermentation properties and microbial diversity of soy sauce fermented by germinated soybean

BACKGROUND

The quality of commercial soy sauce is variable at present. Technical work is needed to improve the quality and flavor of soy sauce, especially in China. Material is a factor for influencing soy sauce characters in fermentation.

RESULTS

Germinated soybean sauce (fermented by germinated soybean) had a gamma aminobutyric acid (GABA) concentration of 6.83 μg mL-1 , whereas a control (a soy sauce fermented by soybean) had a GABA concentration of less than 2.42 μg mL-1 . Germinated soybean sauce also contained significantly higher levels of isoflavones, total polyphenol, and amino acid nitrogen than the control soy sauce. Microbial diversity results showed that Bacillus was the dominant bacteria in germinated soy sauce compared with the control. Aldehydes, alcohols, esters, and phenols were the major flavor components of germinated soybean sauce.

CONCLUSION

A soy sauce with high levels of GABA, isoflavones, and total polyphenol was developed using germinated soybean. Stenotrophomonas, the typical pathogen found in the control, was reduced dramatically and replaced by Bacillus during fermentation with the germinated soybean. The germinated soybean sauce exhibited a better aroma and taste than the control. Soy sauce fermented by soybeans that germinated for 48 h exhibited greater advantages than soy sauce that germinated for 24 and 72 h. © 2020 Society of Chemical Industry.

Preparation of soy sauce by walnut meal fermentation: Composition, antioxidant properties, and angiotensin-converting enzyme inhibitory activities

Remaining walnut meal after oil extraction still contains many nutrients. However, these by‐products have not been effectively used. In this study, walnut meal and Aspergillus oryzae (3.042) were used in combination to prepare a soy sauce‐like material with high amino nitrogen content (ANC). The optimal conditions for the preparation of walnut soy sauce (ratio of brine:koji of 1.7:1 for 6 days at 45°C) were determined using response surface experiments (RSE), which showed maximum ANC of 855 mg/100 ml. The results of amino acid analysis indicated that walnut soy sauce had a similar amino acid composition compared with three commercial soy sauces. It contained all the essential amino acids and had a high content of umami amino acids such as Glu and Asp, which may give it a stronger umami taste. Moreover, the crude walnut soy sauce was extracted sequentially using ethyl acetate, n‐butanol, acetone and water, and the total phenols, total flavonoids, reducing sugars, and the peptides of different solvent extracts were measured. Results showed that the total phenolic and flavonoid contents were highest in the ethyl acetate extracts. However, water residue had the highest levels of reducing sugars and peptides. In vitro, the water residue showed the highest antioxidant capacity and angiotensin‐converting enzyme (ACE) inhibitory activity, due to more reducing sugars and peptides. These results indicated that walnut soy sauce may have significant antioxidant and ACE inhibitory activity. The findings provide a scientific basis for developing a replacement for soy sauce and broaden the beneficial application of walnut meal.

Effects of koji-making with mixed strains on physicochemical and sensory properties of Chinese-type soy sauce

BACKGROUND

Two kinds of soy sauces were prepared with Aspergillus oryzae koji (SSAO) and mixed koji (SSAOM, A. oryzae mouldstarter:Monascus purpureus mouldstarter = 1:2, w/w) respectively. The effects of mixed koji on the essential indices, oxygen radical absorption capacity, color indices, free amino acids and volatile compounds of soy sauce have been studied, followed by a sensory evaluation between SSAO and SSAOM.

RESULTS

The contents of non-salt soluble solid, reducing sugar, total acid, total nitrogen and amino nitrogen in SSAOM increased by 21.50%, 9.88%, 15.35%, 5.98% and 41.43%, respectively, compared with the control SSAO, owing to the higher activities of acid protease and glucoamylase in the mixed koji. Moreover, SSAOM showed higher antioxidant activity, higher levels of free amino acids and much more attractive color. Meanwhile, flavor groups such as esters, aldehydes, pyrazines and sulfur-containing compounds in SSAOM were also improved. The contents of free amino acids and aroma compounds were consistent with the sensory evaluation. According to descriptive sensory analysis, SSAOM showed higher intensity for sweet and umami attributes; in addition, higher flowery, burnt, fruity and caramel-like attributes were perceived in SSAOM, while SSAO showed higher ethanolic and sour attributes.

CONCLUSIONS

The investigated soy sauce prepared with mixed koji can be considered as an effective method to accelerate the fermentation process and improve the flavor of soy sauce.