| With the increasing demand for fast food market, the development of Chinese fast foodhas entered a rapid period. The quality requirements are also higher. In the production anddistribution process of cold-chain vegetable dishes, it needs to go through the hightemperature cooking, low temperature preservation, and microwave reheating treatment. Thequality of cold-chain vegetable dishes had changed a lot because of the large temperaturerange and storage time. It restricts the scale development of Chinese fast food. At presentcold-chain Chinese fast food is mainly meat dishes, and the researches on the cold-chainvegetable dishes are rare. Consumer demands for vegetable dishes and the development statusof cold-chain vegetable dishes determine the research on applicable species and a workableproduction line of cold-chain vegetable dishes to have practical significance.In this paper, the qualities of common vegetables after reheated and conventional cookedwere compared to determine the applicability of cold-chain production. And systematic studyand optimization on the suitable cooking methods and cooling technology of cold-chainvegetable dishes to povide technical guidance and theoretical reference for cold-chain Chinesefast food.And on this basis, it researchs on variation and quality control of vegetable dishes,and establishes shelf life prediction model. The research results are as follows:（1）The research was on the applicable species of cold-chain vegetable dishes. Exceptleafy vegetables, the total bacterial of other vegetable dishes can reach a relatively low levelin its required cooking time, which is favorable to shelf life. Based on the quality standard ofconventional cooking vegetables, the quality after reheated of yellow dishes (potato andpumpkin), green dishes (lettuce, broccoli), and cauliflower class vegetables maintain goodfrom the indicators of vitamin C, color values, hardness, sensory. These types of vegetableshad stronger applicability to cold-chain way.The quality after reheated of leafy vegetables hadserious changes.（2）The effects of different cooking methods on cold-chain vegetable dishes qualitywere studie with lettuce as study object. The results showed that the nitrite content of lettuce(refrigerated for72h at10℃) under four cooking methods was no significant difference (P>0.05). However, blanching and frying methods can strengthen the heat transfer uniformity and stability of lettuce during cooking process which ensures the stability of the number ofmicroorganisms after cooked and remains in a lower range. It is important to the shelf life. Inaddition, the effect of cooking methods on hardness of lettuces after cooked was notsignificant (P>0.05). And the fried lettuce after cooked has the deepest green color. Thecooking methods impacting on cold-chain lettuce was needed to consider the quality changesof refrigerated lettuce after reheated. From results, blanching lettuce after reheated had aminimal change in a*value which increased6.6%, maintaining the best green. But the friedlettuce had a maximum change which increased33.0%. In addition, the hardness of lettuceafter reheated had a greater degree drop. The blanching lettuce had a minimal change whichdecreased17.5%, while the fried lettuce decreased66.0%. And the hardness of microwavecooking lettuce after reheated had a maximum volatility that the standard deviation reached1005. It determined blanching cooking method as the best cooking method of cold-chainlettuce dish with comprehensive consideration. Meanwhile, the experiments show that45sblanching time for cold-chain lettuce dish is the best which can control microorganisms in alower range and maintain maximum quality.（3）The vacuum cooling influence factors of cooking lettuce and the variation oftemperature and weightlessness rate in vacuum cooling process were researched in this paper,with blanching cooking lettuce in tray as research object. Results showed that in the vacuumcooling process, the temperature difference between the center and the surface position ofcooking lettuce in tray is very small, not more than1.73℃, and the temperature difference isonly0.23℃when cooking lettuce temperature reaches10℃. In addition, the cooling rateof cooking lettuce with1.0kg mass decreases with the condensation temperature andincreases with cooling capacity. And when cooling capacity of37.5kg increases to150kg,the cooling time of cooking lettuce with1kg mass effectively shortens by46.34%. Vacuumcooling also causes weight loss of cooking lettuce, with1%of weight loss can bring about7℃temperature decline. In addition, this paper proposes a two-step vacuum cooling mode, toeffectively reduce energy consumption which is only47.29%of energy consumption oftraditional vacuum cooling, and also lower condensate system equipment requirements byreducing the maximum condensate load.（4）The study was on the quality variation of lettuce dishes during refrigerated under 0~10degrees celsius, and established its shelf life prediction model. The results showed thatat each temperature, the total bacterial count, nitrite content and a*value were rising with therefrigerated time, while the hardness, sensory evaluation results showed a downward trend.The higher the refrigeration temperature, the greater the quality indicators change. The end ofshelf life of each quality indicator was compared, and determined a*value to be theevaluation index of cold-chain lettuce dish shelf life prediction model. And established thekinetic model and Arrhenius equation of a*value ratio (at*/a0*) which R2were greater than0.95. The results show that the relative error of cold-chain lettuce dish’s predicted andobserved shelf life was less than6%from0to10degrees celsius. It shows that in thistemperature range, using this model can quickly and accurately predict the remaining shelflife of cold-chain lettuce dish.（5）The research was on total bacterial count variation and growth prediction model ofcold-chain cabbage and lettuce dishes. The results show that the higher the storagetemperature, the bigger the maximum specific growth rate (μm) and the shorter the growthdelay (λ). In addition, at the same temperature, the μmvalue of lettuce which had less initialbacterial count was smaller than cabbage dish, and the λ value was bigger than cabbage dish.From0to10degrees celsius, logistic model can fit the growth dynamic of total bacterialcount of cold-chain cabbage and lettuce dishes which R2were greater than0.99. Theexperiment established the shelf life prediction model for total bacteria of cabbage and lettucedishes by combined with the square root model. And using this model can quickly andaccurately predict the total bacterial count shelf life of cold-chain cabbage and lettuce dishesfrom0to10degrees celsius. |
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