Preparation And Application Of Starter Cultures With Super Concentration And High Activity For Fermented Sausages

The main research contents are as follows: (1) Strains for fermentation were isolated and purified from traditional sour meat. According to their growth profile and metabolism characteristics, the strains with properties suitable for use as starter cultures in sausage fermentation were selected. And the isolates were identified by morphological, biochemical, and physiological characteristics and sequence analysis of 16S rDNA; (2) Based on nutritional requirement for the growth of lactic acid bacteria, the enrichment medium of LAB was optimized. The effects of nitrogen source, carbon source, growth factor and buffer salt were evaluated via orthogonal design. And the medium composition concentrations were determined for maximizing the growth of LAB. By using single factor experiments, the optimum conditions for the strain, such as inoculation quantity, initial pH, fermentation methods were determined; (3) The strains were applied as starter cultures with super concentration and high activity for the production of fermented sausages. During manufacturing of fermented sausages, physico-chemical properties, such as pH value, water activity, meat color and microbiological properties were studied. And product indexes of fermented sausages by the strains selected were measured, compared to sausages fermented naturally and with a commercial meat starter culture.1. Twenty one strains of lactic acid bacteria were isolated from traditional sour meat. Among them 4 strains were investigated for their growth profile and metabolism characteristics according to the special conditions of fermented sausages. All 4 strains could adapt to the special fermentation conditions well, also have good metabolism properties. According to growth curve and pH value change curve, relatively good growth properties and souring properties were found. As a result, they have properties suitable for use as starter cultures in sausage fermentation. The isolate ZJ3-8 was characterized by PCR amplification using 16S rDNA bacteria amplification general primer. Sequences were aligned in GeneBank to determine the closest known relatives of the partial 16S rDNA sequence obtained. Combined with the results of morphological, biochemical, and physiological characteristics, the isolate ZJ3-8 was identified as Lactobacillus farciminus. 2. The medium composition and culture conditions for Lactobacillus farciminus were optimized. Based on nutritional requirement for the growth of Lactobacillus farciminus, the enrichment medium composition of Lactobacillus farciminus was determined: glucose, soybean tryptone, carrot extract, Na₂HPO₄. And the medium composition concentrations were determined for maximizing the growth of Lactobacillus farciminus. The enrichment medium was as follows: glucose 1.0%, soybean tryptone 1.0%, carrot extract 1.0%, Na₂HPO₄ 0.75%, beef extract 0.5%, yeast extract 0.5%, tween 80 0.1%, pH value 6.5-6.7.By using single factor experiments, the optimum conditions for the strain were determined. The optimized conditions were as follows: inoculation quantity=5%; temperature=30℃; initial pH=6.5; static culture. And the LAB growth curve showed that 16-18h was the optimum time for harvesting.3. The starter cultures with super concentration and high activity for fermented sausages were prepared by the selected strain of Lactobacillus farciminus, and were used for the production of semi dried fermented sausages. During the manufacturing of fermented sausages, meat color indexes have significant changes. Sausages inoculated with starter cultures and naturally fermented had similar trends in meat color: the decrease in L^* value and b value, the increase in a value. A decreased trend was noted for pH value both in sausages inoculated with starter cultures and naturally fermented. The pH value of sausages fermented with starter cultures dropped fast, while naturally fermented sausages had a slow pH value decrease. At the end of ripening, both sausages inoculated with starter cultures and naturally fermented had a partial increased trend. The PCA number of both two sausages increased to a maximum, and decreased slowly during ripening. The PCA number of sausages fermented with starter cultures remained below 10⁶ cfu/g, while naturally fermented sausages remained above 10⁶cfu/g. The number of LAB increased slowly after 48h, and remained the count of 10⁸cfu/g. Sausages inoculated with starter cultures had higher total nitrogen and NPN content than two control samples (P<0.05). Nitrite content of sausages fermented with starter cultures was lower than two control samples (P < 0.05). The lipid oxidation level of sausages fermented with starter cultures was lower than two control samples (P < 0.05). No significant difference in FAA content between two control samples and sausages. It indicated that the effect of the starter cultures on the lipid fraction of fermented sausages was not significant.