Screening Of Antifungal Lactic Acid Bacteria And Its Application In The Steamed Cake

Steamed cake is a kind of cake with chinese traditional characteristics.Steamed cake is made by steamed technique,so fine organization and soft palate were popular with modern people.But water content of steamed cake is up to 28~30%,it is one of the most difficult to storage in the pastry.Metabolites of Lactic acid bacteria have bacteriostatic activities.Sourdough with lactic acid bacteria fermented can effectively improve product quality and nutritional value.Sourdough fermented by lactic acid bacteria with high bacteriostatic activities was applied to the steamed cake.It could effectively extend the shelf life and improve the quality and nutritional value of steamed cake.This study aimed to isolate and screen the high antifungal lactic acid bacteria(LAB)from the traditional fermented food by Oxford cup method and 96-microwells plates method,and analyze bacteriostatic components of lactic acid bacterial and identify lactic acid bacteria by the molecular biology.The freeze-dried sourdough was used to substitute for the cake flour at equal amount s and studied the influences on cake batter,steamed cake quality and microorganisms.Main contents and conclusions were as follows:Main microorganisms in the steamed cake were analyzed by the traditional method of separation,purification and identification.Steamed cake had seven kinds of bacteria after 16 S rRNA gene amplification and 11 kinds of fungi(1 kind of yeast and 10 kinds of mold)after 26 S rDNA gene amplification.Staphylococcus and Kocuria were major corruption bacteria.Penicillium,Aspergillus and Cladosporium were major corruption molds in steamed cake.Penicillium and Cladosporium sphaerospermum were main molds early and Aspergillus niger and Aspergillus flavus in the late storage of steamed cake.A total of 300 LAB strains were isolated from the traditional sourdough,fermented rice and fermented grains from different place.25 LAB with antifungal activity to main molds in steamed cake were screened by 11 LAB were got by O xford cup method and micro-well plate method DT0-7,DT2-4 and CT1-4 had good antifungal activity.Based on 16 S rDNA gene sequencing,DT0-7 and DT2-4 were identified as Lactobacillus plantarum(Lp),while CT1-4 was identified as Weissella cibaria.DT2-4(Lp)was used for the following application in sourdough fermentation since it had a greater antifungal ability.The antifungal activity of DT2-4(Lp)fermentation supernatant was analyzed by different pH,enzyme,temperature and hydrogen peroxide treatment.The results showed that main antifungal substance was organic acids.Organic acids were analyzed by high performance liquid chromatography(HPLC)and Gas C hromatography-Mass Spectrometer(GC-MS).The contents of phenyl lactic acid,lactic acid and acetic acid were respectively 95.91 mg/ L,14.81 mg/L and 2.94 mg/L by HPLC.It contained succinic acid,acetic acid,benzoic acid,citric acid,azelaic acid,palmitic acid,linoleic acid and stearic acid by GC-MS.Cake flour was selected as sourdough fermentation substrates for Lp.Optimization of sourdough fermentation was carried out by response surface experiment based on single factor experiments.DY 190,21% inoculation amount and fermented for 24 h at 38°C was found to be the optimal sourdough fermentation condition.In this condition,the inhibition rate of Lp sourdough was was 75.74%.The results of organic acids was determined by HPLC as follow: the phenyl lactic acid was 3.99 mg/100 g,lactic acid was 0.52 g/100 g,and acetic acid was 0.62 g/100 g.The results of organic acids was analyzed by GC-MS as follows: succinic acid,benzoic acid,citric acid,azelaic acid,palmitic acid,linoleic acid and stearic acid.Cake flour was instead of different proportion of lactic acid bacteria fermented flour(0%,25%,50%,75%)in making steamed cake.The results of RVA showed that sourdough fermented flour was less gelatinized and recrystallization,and could delay aging.Cake batter rheology showed that with the increasing of sourdough fermented flour replacement rate,cake batter viscosity increased significantly than the blank group.It showed that the cake batter system was more stable than the blank group.The quality and flavor of steamed cake adding sourdough fermented flour were better than the blank group.Different substitution rates of sourdough fermented flour in steamed cake had influences on microorganisms of steamed cake as follows: Total number of colonies of the steamed cake with adding sourdough fermented flour were less than blank group.With the increasing of substitution rate of sourdough fermented flour,the total number of colonies decreased.The total amount of fungi in the steamed cake with adding sourdough fermented flour were less than blank group.With the increasing of substitution rate of sourdough fermented flour,the total number of fungi decreased.Adding sourdough fermented flour could effectively inhibit the growth of molds in the steamed cake.