Correlation between Pattern of Nitrogen Transformation and Process Control during Fermentation of Rice Dreg Protein for Sauce Production
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Abstract:
Rice dreg protein (RDP) was used as the main material for fermentation to produce sauce, and the correlation between the process control and nitrogen transformation pattern during the fermentation was investigated. The fermentation temperature, salt concentration, amount of added brine, and other control conditions were optimized via dynamic monitoring of the changing patterns of total nitrogen content, amino nitrogen content, soluble protein, and total nitrogen conversion rate in RDP sauce during a 30-d fermentation. The amino nitrogen and total nitrogen contents of RDP sauce and soy sauce obtained under the same conditions were compared, and the antioxidant activity of RDP sauce was evaluated preliminarily. The results showed that the conversion of nitrogen in RDP sauce peaked on the second day of fermentation at 50 ℃; fermentation at 35 ℃ required a longer duration, favored the conversion of nitrogen, and yielded a high-quality product. Moromi with a salt concentration of 11% was conducive to conversion of nitrogen. When the amount of brine was 2.2, 2.5, and 2.8 times as much as the koji weight, no significant effects on the total nitrogen and amino nitrogen contents were observed, while a higher amount of brine promoted the degradation of RDP protein and increased the total nitrogen conversion rate in RDP sauce. Based on this comprehensive analysis, the optimized processing conditions were as follows: the amount of added brine was 2.8 times the koji weight; the fermentation temperature was below 35 ℃; and the salt concentration of the moromi was 11%. Under these conditions, an RDP sauce with a total nitrogen conversion rate of over 70% was obtained. The amino nitrogen and total nitrogen contents of RDP sauce were significantly higher than those of soy sauce, and RDP sauce possessed significant antioxidant activity.
