Study On The Compound Biological Preservatives Application In Dried Bean Curd And The Mechanism

Dried bean curd is one of the preferred non-fermented soy products,which is a kind of historical and cultural food in China.They are rich in protein,fat,carbohydrates,such as easy to breed microorganisms,its short shelf life affects the quality of sale.So the main problems is how to prolong their shelf-life,and the main solution is to use preservatives. Therefore,it is very important to develop compound biological preservatives with wide range of antibacterial spectrum in which are used in dried bean curd industry.The effect of nisin,citric acid,and natamycin on shelf-life extending of dried bean curd was studied.The main conclusions of the experiments were as follows:1) The result indicated that triggered dried beancurd corruption and degeneration is the main species of bacteria,a total of 11 kinds,9 gram-positive bacteria,2 gram-negative bacteria.Simultaneously the fungus is the secondary bacteria species,obtains the yeast and mold each one kind.Through the results of isolation and identification,we could determine the initial bacteria species,the main bacterias include:B is belong to the Bacillus of Bacillus group,df2,df7 are the Aerococcus of Streptococcaceae,C,df5 are the Staphylococcus of Micrococcaeae,df6 is the lactobacillus of Lactobacillaceae,Y0 is Lactobacillaceae,Y1 is the Streptococcaceae of Peptococcaceae,Y3 is the Aeromonas of Vibrionaceae,Y7 is the Lucibacterium of Vibrionaceae,Y8 is the Ruminococcus of Peptococcaceae.2) The experiments of effect on bacteria of preservatives were done when the initial concentration solution bacteria was 10~3cfu/mL.The best antibacterial concentration was 1.5mg/mL Nisin mixed with 1.25mg/mL citric acid.3) The inhibitory effect of natamycin on mildew and microzyme inhibition was studied.When the initial concentration of spore suspension of mildew and microzyme solution were both 10~3 cfu/mL,0.5mg/mL natamycin could completely inhibit the growth of mildew and microzyme.4) Nisin,citric acid and natamycin were used as preservatives to inhibit microbe in dried bean curd.It was found that the growth of microbes could be effectively inhibited with Nisin 0.045g/kg,citric acid 0.038g/kg and Natamycin0.015g/kg and the dried bean curd remained a good sensory quality,shelf-life extended more than 20 days.Also biological preservatives had better effect either on the inhibition of microbes or the safety compared with potassium sorbate.5) Adding preservatives bacteria after freeze-drying bacteria,observed cell morphology in the electron microscope,and we found that cells with preservatives are smaller than strains cells without preservatives,presumably because of cell rupture resulting in leakage of cytoplasm,so they inhibit the effect of cell grow.