Optimization of pre-fermentation process of paste sufu with mixed-strain fermentation by response surface methodology
In order to meet the diversified market demand for sufu,paste sufu was prepared by mixed-strain fermentation.The pre-fermentation condi-tions were optimized by response surface method using protease activity as evaluation index,and the physicochemical indexes,free amino acid frac-tions and sensory evaluation of paste sufu were determined.The results showed that the optimal technological conditions for the pre-fermentation of paste sufu by mixed-strain fermentation were as follows:Rhizopus oligosporus:Mucor:yeast:Lactiplantibacillus plantarum ratio 4:2:2:2,inoculum con-centration 1.0x106 CFU/ml,fermentation temperature 32 ℃,and time 60 h.Under these conditions,the protease activity of the paste sufu was 123.84 μg/g,which was significantly higher than that of R.oligosporus(90.07 µg/g)and Mucor(102.14 μg/g)single-strain fermentation(P＜0.05).The total free amino acids at the end of the pre-fermentation was 5.77 mg/g,of which 34.35％were essential amino acids at 1.98 mg/g,whereas the total free amino acids of sufu fermented by single-strain of R.oligosporus and Mucor were 4.25 mg/g and 3.66 mg/g,respectively.Compared with the sensory evalua-tion results at the pre-fermentation end point of the paste sufu with single-and mixed-strain fermentation,the paste sufu fermented by mixed-strain had the highest overall score,with strong aroma and rich flavor.On the whole,the paste sufu fermented by mixed strain was superior to the sufu fer-mented by singlestrain in all aspects.
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