Study On The Processing And Preservation Technology Of Cooked Prepared Vegetable Dishes

There are abundant vegetable resources in China. A lot of vegetables are available in thetraditional forms of dried, salted and juiced. But the cooked prepared vegetable dishes withsoft package, which represented the new convenient food, rarely appeared on the market. Thisis mainly because the vegetables with fragile texture are difficult to endure the high strengthof thermal sterilization, and it is not easy to maintain a prolonged shelf life only by addingpreservatives which were conformed to standard. Considering those problems, the objectivesof this paper were to research the processing and preservation technology of the cookeddishes which mixed with several raw vegetable materials, ensure a long shelf life, guaranteethe quality of the products, get the commercial value and create the conditions to realizeindustrialization.In order to solve the color, texture and other quality problems of white radish and carrotsin the processing, both blanching and fragility protecting pre-technologies were researched.The peroxidase (POD) inactivation was judged according to the guaiacol method. Theblanching technology was determined that the blanching temperatures of both the shreddedwhite radish and carrots with size of3mm×3mm×30mm were100℃, the blanching timewere120s and150s, respectively. With the hardness and sensory evaluation as indicators, thefragility protecting technology was determined that0.3%CaCl2,20minutes for white radishand0.3%CaCl2,30minutes for carrots. In order to reduce the water content and extend theshelf life, the hot air pre-drying technology was researched. With the hardness, spring andsensory evaluation as indicators, the hot air drying technology were determined that theshredded white radish and carrots were dried at the temperater of60℃for40minutes and20minutes with59.7%and53.6%of water loss, respectively.In order to process the cooked dishes with good taste and color, a L8(27) orthogonal testwas used to determine the ratio of raw material:25%carrot after drying,20%white afterdrying,20%pickled cabbage,18%pickled cucumber,1.5%soybean oil,2%vinegar and3%salt. The pH was reduced to meet the requirement of acidification food by adding0.05%～0.2%citric acid.In order to control the microbes and keep quality, the combined effect of nano-ZnO andthermal sterilization was researched. The better sterilizaiton technology was determinedaccording to compared the microwave sterlizaiton with the pasteurization. Compared withpasteurization, the texture and color of the products kept by microwave sterilization werebetter while the total plate count was not kept well. What’s more, the significant differenceswere not existed between the two sterilization methods at sensory evaluation. Therefore, thepasteurization was chosen for this research. In order to research the effect of Ultravioletirradiation on the antimicrobial activity of nano-ZnO, a test was studied compared withsunlight and dark conditions. The antimicrobial activity of10mL0.1%nano-ZnO wasenhanced effectively when the Ultraviolet irradiation time was40min. In order to researchthe antimicrobial activity of nano-ZnO, the single and compound preservatives werecompared with the total bacterial count, mould and yeast as indicators. The compoundpreservatives which included potassium sorbate, Nisin and nano-ZnO showed the best antiseptic effect. In order to research the application of hurdle technology in cooked dishes, aL9(34) orthogonal test was used with the total bacterial count and sensory evaluation asindicators to determine the optimum combination: the temperature of sterilization was90℃,the time was25minutes, the dosage of citric acid was0.15%, and the preservative’scombination were0.1g/kg potassium sorbate+0.06g/kg Nisin+0.01g/kg nano-ZnO.In order to predict the shelf life of cooked vegetable, the Gompertz equation was used tofit the microbial growth under different storage conditions. The shelf life of products at roomtemperature and cold storage were135days and226days, respectively. The various qualitiesof products had better storage stability during both room temperature and cold storage.