Strain screening, domestication and process optimization of fermented peanut milk

【Objective】 To screen and domesticate the strains suitable for fermenting peanut milk, and optimize the fermentation process, in turn, provide the basis for the production of fermented peanut products.【Method】 Used Lactobacillus Bulgaricus(Lb), L. casei(Lc), L. plantarum(Lp) and Streptococcus thermophilus(St) to ferment Yunnan red peanut. By using thetissue status, fermentation flavor and acidity of fermented peanut milk as the indicators to screen the best strains. After domesticating, the best strains were used to ferment peanut milk, and the fermentation conditions were optimized by single factor experiment and response surface methodology(Box-benhnken). Acidity and sensory score were used as evaluation indexes.【Result】 Lb and Lc were most suitable for fermenting peanut milk, with an Lb to Lc ratio of 1:1. After domestication, the curdling time of peanut milk fermented by strains was shortened by 1.5 h. On this basis, the fermentation conditions were further optimized. A quadratic regression equation had been established between acidity (Y₁) and sensory score(Y₂) on inoculum size(A), sugar amount(B), liquid-solid ratio(C), and fermentation time (D). The optimized model equation was Y₁=72.36 + 10.01A-3.57B + 0.2525C + 11.06D-1.53AB-0.915AC + 0.5325AD-1.84BC-1.83BD-1.07A₂-7.24B₂-8.88C₂-14.38D₂;Y₂=86.22+4.58A-1.02B+0.6917C+4.76D-1.65AB-0.6750AC+ 2.27AD-0.75BC-0.4BD+2.0CD-3.55A₂-4.21B₂-2.84C₂-5.26D₂. The effects of the factors decreased in the order of fermentation time>inoculum size>sugar amount>liquid-solid ratio, and the interaction between inoculum size and sugar amount, sugar amount and liquid-solid ratio, sugar amount and fermentation time on the acidity of fermented peanut milk was significant(P<0.05, the same below), while extremely significant effect was observed for the interaction between inoculum size and sugar amount, inoculum size and fermentation time, liquid-solid ratio and fermentation time on peanut milk sensory score(P<0.01), and the interaction between inoculum size and liquid-solid ratio, sugar amount and liquidsolid ratio had significant effects on sensory scores of fermented peanut milk. The optimized process parameters were:6% inoculum, 5% sugar content, 1:8 for the ratio of material to water, and 11 h fermentation time. Under this condition, the acidity of fermented peanut milk was 74.37 °T, the sensory score was 86.7, these were close to the theoretical prediction. Peanut milk curd is better, the color is milky yellow.【Conclusion】 The most suitable strains for fermenting peanut milk have been screened and acclimated, and the best fermented peanut milk process has been obtained by using response surface optimization, and fermented peanut milk product enjoys suitable acidity, high sensory score, and good flavor. This paper can provide guidance for the development and production of healthy peanut products.