Identification Of Staphylococcus Spp. Isolated From Hunan Bacon And Its Mechanism Of Aroma-production

Fermented meats are nutritious, with special flavor and a long shelf-life, which are popular among consumers and have a good potential for industrialization. However, the starter culture used for meat fermentation depends on import right now, which perhaps will be a limited factor for development of fermented meats. In China, there are a variety of traditional fermented meat products which contain lots of microorganisms. Some of these microorganisms with excellent properties for fermentation can beisolated and developed as starter cultures for meat fermentation.Hunan Bacon was used for current study. The changes of microflora and volatile compounds during process were analyzed. The results showed that the dominant microorganisms in traditional and industrial Hunan Bacon were Staphycocci (10⁶ cfu/g) and LAB (10⁵ cfu/g) respectively. Smoking has significant effect on the microflora. Terpenes were the main volatile compounds at the end of curing; however, after smoking, the major volatiles were guaiacols and heterocycles. Microorganisms had a great influence on the flavor of traditional Hunan Bacon.Staphylococcus strains were isolated from traditional Hunan Bacon and screened for their capability of aroma production. A strain named S52 was selected for its ability to produce high level of 3-butanal, possession of nitrate reductase and catalase, and its antioxidative capacity. S52 was identified as Staphylococcus simulans by examining its biochemical characteristics and 16S rRNA. The optimal temperature and pH for its growth were 37℃ and 7.5. Without salt and nitrite, S52 showed maximal production of nitrate reductase and maximal antioxidive capacity at 30℃ and pH 7.0.The catabolism of leucine by S52 required a-ketoglutarate, which indicated an aminotransferase was involved in the first step of leucine catabolism. At the same mole concentration of BCAA, S52 showed the highest activity for catabolism of leucine and the lowest activity for valine. Different levels of inoculation resulted in different BCAA metabolites. The metabolites were mainly aldehydes and acids when the level of inoculation was 10⁹cfu/ml, however, alcohols, acids and esters were produced when the level of inoculation was 10⁸cfu/ml. The optimal temperature and pH for production of 3-methyl butanal were 40℃ and 7.0, but NaCl and NaNO₂ inhibited its production. In the model system using linoleic acid, S52 produced methyl ketones by incomplete β -oxidation, which contributes to the formation of dry-cured flavor.This S52 was used for the production of fermented sausage. Sensory evaluation showed that there was no difference between sausages fermented with S52 and fermented with commercial starter culture. At the end of fermentation, more volatile compounds were detected in the groups of S52 and commercial starter culture than that of control without starter culture. However, the amounts of volatile compounds in all groups increased at the end of production. As metabolites of BCAA are important elements of dry-cured flavor, the highest yield of volatile compounds derived from BCAA was found in the group of S52, which showed that S52 was suitable to use as starter culture.