| Recently, freshly prepared products have been demanded and have led to the development of a new variety of meat products. For their convenience, nutrition and low price, freshly prepared chicken products have become very popular. However, there are also some problems which have restricted their development.Freshly prepared chicken products are not heat-treated during processing. Many micro-organisms easily grow under refrigeration conditions, especially psychrophilic bacteria. Thus, these products spoil easily and have a very short shelf-life. At the same time, it is very difficult to determine the shelf-life quickly and effectively only by sensory. And it always lags out to determine the shelf-life by traditional means of microbial detection. So a rapid and effective method for shelf-life determination is demanded at present. This research is one of the key parts of the item of"Comprehensive preservation of prepared chicken products"which is the national"11th five– year"technology support program. The purpose of this paper is to analyze the bacterial community of the freshly prepared chicken products for the study of shelf-life prolonging and shelf-life modeling, and to develop a shelf-life predictive model for these products to get a rapid and effective method for shelf-life determination. The aim is to provide a theory basis and guidance for the preservation of the freshly prepared chicken products during production, storage, transportation and sale in order to avoid economic losses. The contents and results are as follows:1 Microbial survey on processing of prepared chicken productsIn order to understand the microbiological quality of prepared chicken products during processing, microbiological qualities of the course of production and the environments were surveyed. The course of production surveyed included slaughtering, partition, prepared processing and final products. The environments included the air, water and contact surfaces. The results showed that 1) the total viable counts of carcasses and parts were between 2.12~3.95 lgcfu/cm2, which were in good condition; while it was between 4.27~5.78 lg(cfu/g) for final prepared chicken products, which were seriously contaminated, and freshly prepared chicken products have higher microbial numbers, which are more serious. 2) the environments of segmentation-house was in good condition, however, they were seriously contaminated during prepared processing, and the production environments were not acceptable. In conclusion, the environments and contact surfaces had significant effect on the TVCs of final prepared chicken products. Standardization of the manufacturing processes is in great demand for prepared chicken products in China.2 Bacterial diversity and dominant species of freshly prepared chicken products To analyze the bacterial diversity and spoilage-related dominant microbiota associated with freshly prepared chicken products stored in air at 4°C, samples were collected and tray-packaged with cling film and stored at 4°C for analysis. The effect of kinds, factories and storage time was analyzed using PCR-DGGE. Combined with selective cultivation of the dominant bacteria, the dominant spoilage microbiota was determined. The results showed that bacterial diversity varied with different manufacturers and different kinds, and the similarity between bacterial communities tended to increase with storage time prolonged. Such bacteria as Psychrobacter sp., Carnobacterium sp., Pseudomonas sp., Brochothrix sp. and Weissella sp. were detected as the dominant bacteria in freshly prepared chicken products during storage. Our work has revealed the bacterial diversity and dominant spoilage microbiota of freshly prepared chicken products stored in air under refrigeration using PCR-DGGE.3 Spoilage of freshly prepared chicken products during storage and determination of SSOsTo analyze the spoilage of freshly prepared chicken products stored in air at 4°C and to find out the minimum bacteria amount spoilage and SSOs, bone and chicken string was selected as subjects. The physicochemical and sensory evaluation were analyzed during storage, and the correlation of these values with the amounts of Carnobacterium sp., Pseudomonas sp. and Brochothrix sp. were also analyzed. The results showed that the physicochemical and sensory evaluations changed significantly between day 3 and day 5, and the values of color, TVB-N and sensory showed the similar regularity during storage, while the pH value change showed a lag. Carnobacterium sp., Pseudomonas sp. and Brochothrix sp. had high amounts during storage, and showed significant relation with physicochemical and sensory evaluations with higher pearson correlation coefficients. These three species should be the SSOs of the prepared chicken products. The minimum bacteria amount of spoilage was determined as 7.34 lg(cfu/g).4 Microbial growth kinetics models for Pseudomonas sp. and shelf-life prediction for freshly prepared chicken productsBone and chicken strings were selected as subjects in the study. All samples were tray-packaged and stored at 0°C, 4°C, 7°C, 10°C, 14°C and 20°C respectively. The amounts of Pseudomonas sp. were calculated directly from samples during storage. Modified Gompertz equation was used as primary model to fit observed data, and shelf-life model was developed based on the growth predictive model. The results showed that the modified Gompertz equation could give a good description of Pseudomonas in different storage temperature, and the growth predictive models under different temperature were fitted. As a secondary model the square root model was used to describe the relationships of maximum specific growth rate and lag time with temperature. The secondary models developed had good linear relationship, and the absolute values of the residuals were less than 0.05 which indicated that the regression lines were fitted to the original observations in good condition. Another similar experiment was conducted with different batch of bone and chicken strings which were stored under 4°C and 20°C to test the accuracy and validity of the models. The values of Af and Bf were 1.20, 0.93 and 1.16, 0.98 for models of 4°C and 20°C respectively. The models can predict the amounts of Pseudomonas in bone and chicken strings during storage rapidly and accurately. The shelf-life predictive model was developed as a result which can predict the shelf-life of bone and chicken strings under 0 ~ 20°C.
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