Seperation And Identification Of Selected Strain On Fermented Sausage

This thesis describes the isolation and selection of microorganisms from fermented meat products produced in different sites such as Hunan,Hubei,Zhejiang and Jiangsu Provinces. The fermented characteristics,fermented adaptability and freeze-dry resistance capabilities were studied, then the compound strain(I2 and I9) were selected and identified.; Meanwhile, together with the practical produce experience, the selection criteria of sausage strains was discussed in this paper. The thesis concludes the five points as follows.1.Strain I9: it grew well in the MRS culture medium under the condition of 25³0℃;It is negative for H2O2 enzyme, could not deoxidize nitrate, is not aerogenical when fermenting dextrose, and it could not grow in the broth with high concentration (6.5%) of salt; the Sausages had a moderate flavor of sourness and savor and a tarnished surface layer; Ornithine decarboxylase and lysine decarboxylase of I9 were negative while Arginine Decarboxylase was positive. The I9 strain could produce 8.41mg/Kg tyramine, 3.85 mg/Kg putrescine, 7.90 mg/Kg cadaverine, 1.42 mg/Kg histamine, 4.03 mg/Kg spermine and 2.60 mg/Kg spermidine, but none of them could produce tryptophan-amine during the sausage fermentation. The livability of Strain I₉ through lyophilization was 84.6%; According to Bergey's bacteria identification norm and the homogenous comparison of 16 SrRNA serial, I₉ is Pediococcus pentosaceus.2.Strain I2: it grew well in the MRS culture medium under the condition of 30℃; it was negative for H2O2 enzyme activity, could deoxidize nitrate, was not aerogenical when fermenting dextrose, and it could not grow in the broth with high concentration(6.5%) of salt; The sausage made by the compound strains( I₉ and I₂) as starter exhibited a rose color and full-bodied scent. Ornithine decarboxylase and lysine decarboxylase were negative while Arginine Decarboxylase was positive,the compound strains( I₉ and I₂) could produce 3.14 mg/kg tyramine, 1.53 mg/kg putrescine,7.20 mg/kg cadaverine, 3.45 mg/kg spermine and 2.61 mg/kg spermidine, but none of them could produce tryptophan-amine and histamine during sausage fermentation. I9 was proved to be safe through the toxicology experiments carried out by Microbiology Institute of Chinese Science Academy. The livability of Strain I2 through lyophilization was 79.0%; According to Bergey's bacteria identification norm and the homogenous comparison of 16SrRNA serial, I2 is Staphylococcus xylosus.3.I₂ and I₉ have a well symbiosis relationship. Compared to the single starter-I₉, the compound starter of I₂ and I₉ could reduce the amount of biogenic amines including putrescine, tyramine, and cadaverine. And the reduced amount were 2.32mg/kg, 5.27mg/kg and 0.70mg/kg correspondingly. The results indicate that I₂ can inhibit the production of biogenic amines.4. The fragrance ingredients of the fermented sausages were analyzed through the GC/MS method, the result indicates that the compound starter (I₉ and I₂) could produce more ketone substance when compared to Single starter-I₉. The Single starter sausages could produce 5 sorts of ketone substance while the compound could 10, and the amount increased from 21.6% to 40.5%; in addition, butanedione, which is the unique fragrance of fermented dairy products, was detected from the Compound starter sausages. And the amount of butanedione constitutes 10.09% of volatile ingredients, which contributes greatly to the fragrance. Therefore, strain I₂ is an important contributor to the fragrance of fermented sausages.5. Currently, tolerability (a strain grows well in 6% salt and 100mg/kg nitrite solution) and deoxidizability could not be the separation criteria, but could be the referral criteria; the most direct and effective method of strain separation is to experiment on the strains through sausage fermentation, ant then evaluate the sausages through sensory analysis.