Study On The Main Spoilage Bacterium And HACCP Of GDL Tofu

The short shelf life and the deterioration of tofu restrain the development of soybean product in China. The valid method is to industrialize the traditional soybean products and to extend the shelf life of tofu by strict quality assurance/control (QA/QC) on product formulation and processing based on Hazard Analysis and Critical Control Point (HACCP) system.The growth and survival characteristics of the main spoilage bacterium in tofu were studied in this thesis by using the method of predictive microbiology. And predictive models for the effects of environmental factors on growth of microorganism were established. On this basis, at first the critical hurdle factor, which controls the tofu spoilage, can be found. Secondly, HACCP can be established by the objective assessment of the process techniques. Thirdly, the shelf life and microbial quality of tofu can be predicted. Last, those predictive models can also be developed to the important means in the soybean product design. And the shelf life of the unshaped products and the species of microorganism can be predicted. Therefore, it is very important to do the theoretic researches on the growth and survival of the major bacterium for extending the shelf life in tofu.Based on the isolation and identification of the spoilage bacterium in GDL tofu, the microbial growth and survival kinetics of two strains were studied at first. And the processing of GDL tofu coagulation is studied. The sterilization of the processing is also assessed. The extension of shelf life was obtained based on HACCP system. The main detail researches are as following:Isolation and identification the major bacterium were performed on GDL tofu from different aged lots. The dominant microorganisms changed from Bacillus spp. such as Bacillus firmus in fresh GDL tofu to Enterococcus faecium in tofu stored at 37t for 24 h. Samples were taken during the manufacture of tofu, plate counts and organisms characterization in each sample were performed. The spoilage microorganisms were mainly from soybean. Cleaning soybean can decrease the total bacterium counts, especially thermophilic bacterium.2.The effects of temperature, water content and pH on growth kinetics of B. firm us in soymilk were studied. pH was the most prominent factor, so that pH reduction can be the main hurdle. It is available to prevent growth of B. firm us in soybean products by adjusting pH and water content.3.The growth responses of E.faecium as affected by temperature, pH, NaCI concentration, GDL and vacuum were studied in soymilk. Growth curves were fitted using the models of Logistic, Gompertz and Monod functions, and specific growth rates derived from the curves fitted were modeled. The experiments?results were as following:?A study to set up mathematical models that predict the growth of E. faecium in soymilk was carried out. Growth curves were obtained at O-55C. The Gompertz model was found to fit with representation of experimental curves which are typical sigmoidal at 10-SOt. The Monod function was found to fit with the experimental curves below l0tor above 50C. The variations of growth rate with temperature were modeled. Data processing of the model has shown that the minimum growth temperature for E. faecium is 4.8t, the maximum growth temperature is 54.6 慍 and the optimal growth temperature is 41 慍. The reliability of the predictive model was evaluated under controlled conditions using soymilk.?Temperature fluctuations near the minimum temperature decrease the growth rate of E. faeciumIIItand increase the shelf life of soymilk. Actual temperature fluctuation to a high temperature in a short time (2 h) increased the bacteria amounts, decreased the shelf life when samples were stored at 0 C.?The growths of E. faeciwn at 36C, pH 5.20-7.50 were investigated. The results declared that cells were able to overcome the stress rapidly. The optimum pH is 6.0-6.6.?The effects of pH (5.50-7.50) and NaC1 (0-3.5%) on the lag time and growth rate were determined. 0.5% NaCI i...