Effect Of Cooking And Storage On Quality And Safety Of Nutritional Diets

The demand of nutritional diets is rising in big cities with the rapid development of economy. Nutritional diets were designed to provide human rational protein, fat, carbohydrate, vitamin and mineral, et al according to the nutritional needs of human body and the contents of kinds of nutrients in diets. However, food safety accidents occurred frequently in recent years. Therefore, it was very important to study effect of different cooking methods and storage conditions on quality and safety of the nutrition diets. The paper mainly studied effect of boiling and microwave on quality of three kinds of commonly consumed vegetables, and effect of different storage conditions on the safety of nutritional diets. The main conclusions were as follows:(1) Effect of boiling and microwave on quality of spinach, cabbage and green vegetables as the raw materials was studied. The results showed that, two kinds of cooking methods both made the color of green leaves deepen. Boiling reduced chlorophyll content of the vegetables leaves while microwave was the opposite. Ascorbic acid content of fresh spinach, cabbage and green vegetables were reduced58.60%,55.57%and27.33%, and the loss caused by microwave was relatively little. Total phenol contents of three vegetable leaves after boiling were significantly reduced, but the contents were increased obviously after microwave processing. Therefore, microwave treatment was better than boiling considering the keep of quality.(2) Effect of different storage conditions (4℃and-20℃) on safety of nutritional diets (cooked rice, fried eggs, dried bean curd, stewed fish blocks and cabbage as raw materials)was studied. The results showed that the values of pH all decreased especially fried eggs. As for color, frozen vegetables were better than the refrigerated, but there were no evident differences on other materials. As for the microorganism, frozen nutritional diets were better than the refrigerated. The number of microorganism was still lower after frozen for49days while the refrigerated nutritional diets couldn’t be eaten after one or two weeks. Therefore, the shelf life was only8days under refrigerated condition while several months under freezing condition.(3) Effect of different storage conditions (4℃and incubator preservation) on the nutritional diets (rice, celery and pork as a raw material) without seasoning was studied. The results showed that during refrigerated storage period, the pH value of rice decreases obviously and the pH value of the celery has downward trend but not obvious. Besides, the pH value of the pork has fluctuation. The microbial quantity of rice during refrigerated storage exceeded standard after6days. Therefore, the refrigerated storage time had better no more than6days, and heat preservation time had better no more than4h. Compared with the nutritional diets without seasoning, the shelf life of nutritional meal with seasoning was longer, which implied that seasoning played a role in the preservation effect.