Study On The Specific Spoilage Organisms And Targeted Inhibition Towards Them In Sliced Vacuum Packed Smoked Cooked Ham

Pasteurized meat products are favor meat products of customers with its proper nutrition and texture such as: enriched fat and protein, fresh and tender of tast, great flavor et al. and will be the way of future development of meat products. But pasteurized meat product has higher A_w and pH value. In addition, pasteurization could not kill all bacteria of product in the processing. So the survival bacteria would growth rapidly when the condition is suitable for its development or have recontamination which will cause for spoilage and resulting in short shelf-life with sensory quality defects such as discolouration, water liquid, oil exudation, ropy slime formation, sour off-flavour, gas production et al. How to prolong the shelf-life of pasteurized meat products is a difficult problem towards the manufactures. Therefore, the study of quality cuntrol and integration protective technology focusing on controlling the spoilage bacteria in these products became the key issue of research and industrialization of pasteurized meat products. The purpose of present study was isolation and identification the predominate spoilage bacteria in one of the representative pasteurized meat products—vacuum packed sliced smoked cooked ham, understanding the dynamic changes in specific spoilage organisms (SSO) of this product, and the effect mechanism of the SSO on the quality of meat products; explaining the formation of spoilage bacteria community, establishing methods to quickly and accurately identify the SSO and trace the main contaminated source; moreover, studying the bioprotective culture target inhibit towards the SSO in pasteurized meat products was carried out; Finally, we would like to provide a theory basis and technique for the ensuring of the quality and safety of pasteurized meat products in the period of prosessing, storage and distribution. The contents and results are as follows:1. Study of the storage characteristic of vacuum packed sliced smoked cooked hamThe storage characteristic of vacuum packed sliced smoked cooked ham under different temperature was studied. The result showed that the vacuum packed sliced smoked cooked ham is a highly perishable meat product with initial pH value 6.42, A_w 0.982, protain content 16.8%, fat content 3.3%, water content 70.3%, and initial total bacteria count of 10¹ï½ž10³ CFU/g. The pH value and L showed downtrend, TVB-N value,solubility protein and a^*,b^* value showed uptrend, and A_w, fat and TBARS value have no changed in significantly during the period of storage.The storage temperature had significant effect on the quality and shelf-life of this product which storaged under low temperature would prolong the shelf-life. The sensory defects of spoilage products were sour off-flavour, discolouration, lackluster, relax texture, loosen elasticity, water liquid, ropy slime formation and gas production. The main elements of spoilage gas include CO₂, alcoholic compound of ethanol, volatility compound of acetic acidetal.The maximum total bacteria count reached 10⁸ CFU/g during the period of storage. Using the maximum bacteria count as level to exitmate the shelf-life of this product in accord with sensory evaluation method. The lactobacillus spp. (LAB) was the predominate microorganisms in vacuum packed sliced smoked cooked ham, Enterobacteriaceae taken second place, Pseudomonas spp., Staphylococci/Micrococcus were in the minority, and sometimes contaminated yeast in products.2. Study on the microbial community dynamic during the period of storage and isolation and identification of the predominate spoilage bacteriaThe microbial diversity and dynamic changes during the storage were explored through PCR-DGGE fingerprinting technique combination of conventional culture method. The result showed that the diversity of the original contaminated microorganism were high. However, the minority specifie spoilage bacteria eventually became the predomination microorganisms during the period of storage. They inhibited the growth of other microorganisms with strong competition ability caused specific spoilage which resulting in bad quality.The main spoilage bacteria were isolated and identified from vacuum packed sliced smoked cooked ham by combination of culture dependent and culture independent methods. They were: Lactobacillus sakei, Lactobacillus curvatus, Leuconostoc mesenteroides and Uncultured Leuconostoc sp. 3. Spoilage microbial effect on the quality changes of vacuum packed sliced smoked cooked hamThe study of microbial effect on products spoilage was carried out by analysised the spoilage potential of microorganism of its can result in the phenolmenal of spoilage and the spoilage activeity of microorganism of its quantitative ability to produce spoilage metabolites. The results showed that:Leuconostoc mesenteroides subsp. mesenteroides was indentified as a SSO that contributed to the quality defect such as "shell off", water liquid, "swell bag", relax texture and discolouration, lackluster. It can utilize the glucose of meat medium to heterofermentate to produce CO₂, acetic acid, propylanol, butyricanol, decompose compound of nitrogen such as protein to make the TVB-N value rise up.Lactobacillus sakei subsp. sakei was identified as a SSO that contributed to quality defects such as sour off-flavor, ropy slime formation. It has preferential fermentation ability to utilize the sugar of meat products to produce lactic acid, acetic acid resulting in pH value drop, exopolysaccharide compound to formate ropy slime, produce representative spoilage compound of tyramine and putrescine resulting in rotten flavour.Lactobacillus curvatus subsp. melibiosus was identified as a SSO that contributed to the quality defects such as sour off-flavor, ropy slime formation, discoloruration and grayness, rotten flavorur. It has preferential fermentation ability to utilize the glucide of meat products to produce lactic acid, acetic acid and ethanol, and exopolysaccaride compound, furthermore, it can make a great deal of representative spoilage compound of tyramine,cadaverine and putrescine when meat products become spoilage.4. Analysis of the diversity of microbial community during processing of smoked cooked hamThe diversity of microbial community of the key processing point was analysed by DGGE technique. Through compared the diversity of microbial community between every susceptibly contamination point, the correlation of these microbial community and predominate spoilage bacteria was obtained. The results indicated that:The main spoilage bacteria of vacuum packed sliced smoked cooked ham are come from the raw meat. The processing of tumbling and the period of chilling after heat treatment are susceptible contamination points.Improper using preservative will bring underlying trouble to the product safety.5. Study of protective effect of bioprotective culture towards the SSOThe effect of Lactobacillus sakei B-2 as bioprotective culture to prolong the shelf-life of sliced vacuum packed smoked cooked ham storaged under 4℃was evaluated. The inhibitory interaction between bioprotective culture and target bacteria was expatiated by characterization of the dynamoic changes of microbial community of meat products during storage under refrigement temperature. The result showed that: The shelf-life of sliced, vacuum packed cooked ham inoculated with L. sakei B-2 at levels of 5.91±0.04 log₁₀ CFU/g was 35 days, compared to the 15 days shelf-life of the control product. Treatment with the protective culture has been shown to suppress the growth of the predominant spoilage bacteria including L.sakei, L.curvatus and Le.mesenteroides but can not completely control the growth of strains of uncultured Leuconostoc.The application of culture-dependent and in-dependent methods led to an understanding of the inhibitory interaction taking place between protective cultures and target strains. PCR-DGGE is an effective technique to analyze the dynamic changes of microorganism population when bioprotective culture applied in pasteurized meat products to prolong the shepf-life. A better understanding of inhibitory interaction between protective cultures and target strains may lead to correct application of protective cultures to meat products.