The Optimization Of Fermented Culture Of Propionibacterium Freudenreichii And The Application Of Its Metabolites On Foods

Preservative is one of the most important additives in the food industry. Nowadays Sodium Benzoate and Potassium sorbate are the widely used chemical preservative. However, studies reveal that these chemical preservatives may lead to some problems inducing carcinogenic effect. It is a trend that bio-preservative replace the chemical preservative in the food industry gradually for the safety reason. As a newly developed bio-preservative, propionicin has been studied intensively by the foreign researcher, however, it has no related report in China to our knowledge, especially on the microbiol inhibition activity. In this paper the metabolites inhibitory activity of a Propionibacterium.freudenreichii using the spoilage organism Pseudomnas.putida and Saccharomyces.sp Y190 as indicator strains.The inhibitory effect of propionibactium metabolite on spoilage organism Pseudomnas.putida and Saccharomyces.sp Y190, and the properties of the metabolites including inhibitory spectrum, and the concentration of the organic acid of the metabolites, and the antimicrobial sensitivity to heat and protolytic enzymes were studied in this thesis.Single Factor Design and Response Surface Analysis have been employed for the optimization of fermertation conditions and the composition of the fermentation medium; the metabolites of P. freudenreichii have been applied in juice and beverages to investigate its antimicrobial activity.The thesis investigated the antimicrobial activity of the metabolites of P. freudenreichii, its antimicrobial scope and the optimized condition for inhibitory experiments. The results showed that the best medium fou the metabolites of P. freudenreichii was medium with carborhadrate source of glucose; the optimal pH for metabolites to inhibit Pseudomnas.putida and Saccharomyces.sp Y190 were 6.0.and 4.0, respectively, and the highest antimicrobial activity is 25.6 AU/ml and 12.7 AU/ml, respectively. The optimal inoculation of P. freudenreichii is 10%. Results showed that it can inhibit the growth of gram negative bacteria, some yeast and fungi, but it can not inhibit the growth of Escherchia coli and the gram positive bacteria.The properties of the metabolites were also studied. Antimicrobial activity of the metabolites was stable in the temperature range of 60℃～121℃for 15 minutes. The metabolites were very sensitive to Pepsin and Trypsin.The optimal culture conditions of metabolites of P. freudenreichii were established. Single Factor Design experiment results showed that the optimal fermentation medium was 20.0g of defatted soybean powder, 20.0g of glucose, 10.0g of yeast powder, 0.25g of K₂HPO₄, 0.005g of MnSO₄, and distilled water1000mL, pH 7.0. Under this culture, the highest antimicrobial activity for Pseudomnas.putida and Saccharomyces.sp Y190 is 20.9AU/mL and 15.6 AU/mL, respectively.The study found that the whey powder, glucose and sodium lactate were the most important factors in the culture of metabolites to inhibit to Saccharomyces.sp Y190. The optimal levels of three important factors were studied by Response Surface Analysis. The optimization composition of the fermentation medium was as follow: 49.0g of defatted soybean powder, 0.6g of Glucose, 0.6ml of sodium lactate, 0.25g of K₂HPO₄, 0.005g of MnSO₄, distilled water 1000mL, pH 7.0. The final inhibitory activity of the metabolites was 19.8AU/mL when fermented with the optimization condition and medium.The result of application experiments showed that the metabolites of P. freudenreichii had strong inhibitory effect on the spoilage microorganisms of juice and acid milk drinks. The total plate counts of microorganisms of juice were more than 10⁷cfu/mL after stored for 7d and 15d at 4°C. When the juice which added with 1% and 5% the metabolites of P. freudenreichii were only 10²cfu/mL of total plate counts. The total plate counts of acid milk drinks were more than 10⁸ cfu/mL after stored at 25°C for 28 days. When the acid milk drinks which added with 1% and 5% the metabolites of P. freudenreichii were only 10⁵ and 10³cfu/mL of total plate counts, respectively.In this thesis we have studied the inhibitory activity of the metabolite of the Propionibacterium, the examination of partial properties of the metabolite and the optimization of culture condition. This has great value on the further use of the metabolite as food preservative in China. Further studies should be carried on to elucidate the detail properties of metabolites as food preservative.