Formulation Optimization and Storage Quality Change of Rice Milk Fermented by Compound Bacteria

Taking rice flour and skimmed milk as the main raw materials, the formulation and storage quality of rice milk were studied based on the optimization of the suitable proportion of compound bacteria in the rice milk. By comparing the fermentation characteristics of the commercial leaven (Lactobacillus bulgaricus and Streptococcus thermophilus) and the Lactobacillus plantarum ZSM-002 in the rice milk, the suitable proportion of the compound bacteria in the fermented rice milk was determined. The formulation of rice milk was optimized by single factor combined with orthogonal optimization experiments (rice water ratio, skimmed milk addition, sugar addition, compound bacteria inoculation scale, fermentation time and fermentation temperature). The centrifugal sedimentation rate was used as the index to determine the proportion of compound stabilizer through uniform design experiment. Finally, the storage quality of optimized rice milk was studied. The results indicated that proper microbes ratio of commercial leaven to ZSM-002 was 3:2. The optimized formula of rice milk was as follows:1:10 (g/mL) of material to water ratio, 3% compound bacteria inoculation scale, 10% skimmed milk, 9% sugar, 0.2% compound stabilizer (propylene glycol alginate of 60%, sucrose fatty acid ester of 0.2%, pectin of 38%, xanthan gum of 1.8%), temperature of 37℃ for 10 h.The centrifugal precipitation rate of fermented rice milk, rice milk acidity, living bacterium and sensory score were 2.25%, (17.03±0.92)°T, (8.53±0.08) lg (cfu/mL) and (8.83±0.20) scores.Under the condition of 4℃ storage after 7 d, the acidity was (34.2±1.56)°T, and the number of living bacterium was (7.44±0.12) lg (cfu/mL). The number of probiotics in Lactobacillus beverage reached 10⁶ cfu/mL. The rice milk was sticky and had a mild lactic acid flavor.