Changes And Control On Quality And Safety Of Green Leafy Vegetables As Bento Side Dishes During Cold Chain

The cold chain fast food industry have developed rapidly, but bento side dishes are mainly composed of meat, but less in vegetables, especially the green leafy vegetables. Green leafy dishes are easy to turn yellow, and microbes and nitrite content grow fast, which easily leads to food safety issues and greatly limits its application as cold-chain dishes. Research on quality and safety changes of green leafy vegetables in the process of raw materials storage, blanching processing, cold storage and microwave reheating and discussion on nitrite accumulation mechanism have a good reference guide to the material storage, selection and cold chain green leafy vegetables dishes processing. And on this basis, the nitrite scavenging ability of color fixatives was studied for green leafy dishes to provide solutions to color and safety issues. The research results were as follows:(1)The qualities and security indicators of nine market cold-chain vegetables dishes were analyzed. The results showed that the total bacterial count of different kinds of vegetables dishes was significantly different after cold storage for 7d at 4℃ and declined after microwave reheating, but it remained highest among leafy vegetables. The nitrite content of leafy vegetables whose color turned yellow was also highest, while the vitamin C content was lowest, which had no goods value. The index changes of root vegetables dishes were less, which had strong applicability to cold-chain. In the current market cold-chain vegetable dishes, we should pay more attention to the safety of leafy vegetables dishes, especially green leafy dishes.(2)The effects of room temperature(20℃) and low temperature(20℃) on quality and safety changes during storage were researched with Brassica campestris L and Chinese flowering cabbage raw materials as objects. Low temperature can delay the quality deterioration of green leafy vegetables. With the increase of storage time, the nitrite content, nitrate content, pH value and respiration intensity had increased on the second day, and then decreased, the nitrite content of green leafy vegetables increased significantly in the room temperature later. And the total bacterial count, the weightlessness rate of green leafy vegetables kept increasing, while the vitamin C content was opposite. In early days of storage, nitrate reductase played an important role in green leafy vegetables. Late in storage, with etiolation and aging of leafy vegetables, the enzyme activity decreased and the vitamin C content became low, so the growth of microorganism played an important role, which made nitrite content high.(3)The effects of blanching, cold storage and microwave reheating on quality and safety changes during cold chain processing were researched with Brassica campestris L and Chinese flowering cabbage as objects. Blanching can significantly reduce the nitrite content, nitrate content, total bacterial count and vitamin C content. The nitrite content of hot water increased with blanching time. The convection heat transfer way through the water as a medium can make nitrite of vegetables dissolute in water. The nitrite content, the total bacterial count increased with cold storage time, while nitrate and vitamin C content decreased. After blanching cooking, nitrite change was mainly associated with microbial activity because of enzyme inactivation. In the early days of cold storage, the nitrite content of vegetables grew and a large number of vitamin C content reduced for its reaction with nitrite. Later, there was no enough vitamin C, so the nitrite content gradually increased. Microwave reheating can make nitrite and nitrate content of vegetables increase, the total bacterial count and vitamin C content significantly reduce and the weightlessness rate increase. Short time microwave reheating can make the nitrite content increase, which mainly because the mass loss rate of vegetables was greater than the nitrite thermal degradation rate. Avoid large area exposure when microwave heating for dishes.(4)Ascorbic acid has strong nitrite scavenging ability among commonly used color fixatives in fruits and vegetables. The effects of salt and ascorbic acid additions on quality and safety changes during cold chain were researched with Brassica campestris L and Chinese flowering cabbage as objects. With tap water, 100 mg/kg ascorbic acid, 1% salt water, 1% salt + 100 mg/kg ascorbic acid solution as blanching water, two vegetables turned green after blanching, while they turned yellow with 500 mg/kg ascorbic acid or 1% salt + 500 mg/kg ascorbic acid solution as blanching water. The nitrite content of vegetables decreased significantly, and it was lowest in using 500 mg/kg ascorbic acid as blanching water while highest in using 1% salt water. During cold storage, the color of dishes with 1% salt + 100 mg/kg ascorbic acid solution as blanching water remained good. The nitrite content increased with time, but 1% salt water group was still the highest and 500 mg/kg ascorbic acid group remained lowest. The higher ascorbic acid concentration, the greater nitrite scavenging ability is, but high concentration will make blanching green leafy vegetables turn yellow.