| Chinese meat production has reached a quarter of the world. The pork industry always occupies a decisive position of meat industry in China, which production and consumption capacity increase year by year. Pork is the most important source of our national food protein. The pork processing methods are mainly based on heating, which includes drying, smoking and boiling, and combined with a variety of traditional cooking methods. While boiling is the most common one in home cooking. Study on different pork boiling and preservation methods are significantly meaningful. In this study, M. longissimus dorsi of pork was used as experimental material, three common heat-cooking method (boiling, stewing and high-pressure steaming) were selected. Firstly, the process of three heat-cooking methods was optimized by fuzzy mathematic evaluation, protein and its degradation products were compared under the three optimum cooking conditions, then method of stewed pork preservation was also studied. The main results were presented as follows:1. Fuzzy mathematic evaluation model was introduced to optimize the process of pork (3 cm X 2 cm X 1 cm). As five key factors, colour, texture and mouthfeel of the cooked pork, taste and odour of the soup were weight ratio analyzed based on sensory evaluation. The integrated assessment system were established. On this basis, different ratios of material to water, boiled temperatures and times were optimized by the method of fuzzy mathematic evaluation. The results showed that the optimum conditions were:1:2 the pork to water,100℃boiled temperature and 30 min boiled time for boiling method; 1:1.5 the pork to water,70℃stewed temperature and 2 h stewed time for stewing method; 1:1.5 the pork to water,15 min high-pressure steamed time for high-pressure steaming method.2. The total nitrogen (TN), water soluble nitrogen (WSN), non protein nitrogen (NPN) and free amino acid (FAA) were detected on the pork as well as its broth obtained by three different cooking methods (boiling, stewing and high-pressure steaming) under the optimum cooking conditions. SDS-PAGE gel electrophoresis were also carried out. The SDS-PAGE profile indicated that after stewing procedure, the high-molecular-mass proteins degraded more effectively and the WSN concentration of the broth was the highest. For the methods of boiling, stewing and high-pressure steming, compared with fresh pork, the pork broth system increased by 12%,24%,5% for the total WSN,42%, 59% and 33% for the NPN, and 40%,46%,33% for the FAA, respectively. In stewing procedure, the protein degraded much more than that in other methods. Moreover, most protein degradation products effused into the broth, which provided the best nutrition and flavour for the stewed broth.3. Stewed-pork soaked in the chitosan (CHI), aqueous extract of ginger, onion and garlic (GOG) and their composite solutions, respectively. Effects on quality and shelf life of stewed-pork were evaluated periodically by the microbiological (total bacterial count), chemical (pH, TVB-N, POV, TBA) and sensory characteristics during refrigerated storage at 4℃for 12 days. CHI and/or GOG treatments retarded the increases in pH, TVB-N, POV, TBA and total bacterial count compared with the control (CON). CHI showed better antibacteria but weaker antioxidation than GOG. In addition, composite treatment had synergistic effect while the high concentration of composite solution (Mixl) had adverse effect on odour and overall acceptance. Mix2, the diluted solution of Mixl, could be a natural promising preservative for the stewed-pork considering the combined effects of antioxidation, antibacteria and sensory quality. |
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