Study On The Separation And Control Of Spoilage Microorganisms In Soy-mung Bean Milk

Soy-mung bean milk becomes popular because of balanced nutrition and no cholesterol. But that's also why spoilage organisms grow and reproduce in it easily, which causes short storage period of soy-mung bean milk. Fast spoilage of bean milk has negative impact on the soybean milk industry. Therefore, study on improving the shelf life of soy-mung bean milk has good prospects in application.The study separated spoilage organisms from soy-mung bean milk, analyzed the samples and identified them, after that, explored the affect of sterilization conditions, storage conditions and pH value on soy-mung bean milk. The experiment chose effective bacteria inhibitor basing on the bacterial characteristic. Several hurdles were studied, including high temperature sterilizing, low temperature storage and inhibitor to control growth of spoilage microorganisms, reduce the amount of bacteria inhibitors and achieve the desired extended shelf-life.At 36±1℃, soy-mung bean milk sterilized on 100℃for 15 min spoilaged in 24 hours quickly. Total count and pH of product changed fiercely. Total count of product increased rapidly from less than 100 cfu/mL to 10~5~10~6cfu/mL. The pH fell rapidly from 6.40 to 5.00 .20 strains from spoilage soy-mung bean milk were identified as bacteria. No molds or yeasts were found. All stains caused deterioration of soy-mung bean milk in 12 hours. 20 strains had similar colony morphology on nutrient agar medium. They were all gram-positive bacteria. Four kinds of bacteria were identified through physiological and biochemical characters. They were Bacillus subtilis, Bacillus cereus, Bacillus megaterium and Bacillus mycoides.The growth characteristics of 4 kinds of bacillus were studied. The results showed that sterilization temperature, sterilization time, storage temperature and pH all influenced on the growth of these bacillus. Their optimum growth temperature was 28~37℃. Storage temperature of below 4℃could completely inhibit their growth. The pH of optimum growth of these bacillus was 6.00~8.00. Even the pH fell to 4.00 or up to 10.00 couldn't inhibit the growth of bacillus completely. Sterilization temperature and time was proportional to sterilization effect, but inversely proportional to quality and stability of soy-mung bean milk. Sterilizing on 100℃for 15 min killed most microorganisms in bean milk, except little thermophile bacteria.Minimum inhibitory concentrations (MIC) of 8 antibacterial agents on 4 kinds of bacillus were studied. The experiments showed that the inhibition of Sodium Diacetate, Nisin, andε-Polylysine was remarkable. The optimization formulation analyzed by Response Surface Method(RSM) was, 0.0483% Sodium Diacetate, 0.0019% Nisin and 0.0066%ε-Polylysine. Inhibitory rate reached 100% by the formula. Soy-mung bean milk contained these preservatives could keep 4 days under 36±1℃, 20 days under 20℃, more than 60 days under 4℃. The results illustrated that the preservatives formulation worked well, greatly extended the shelf life of soy-mung bean milk.