Storage temperature suitability and film permeabil

Adaptability of storage temperature and film permeability of green vegetables packaging III

2.4 changes in VC content in green vegetables storage

figures 5 and 6 show that with the extension of storage time, VC content in green vegetables gradually decreases, and low-temperature storage can effectively inhibit the oxidation of VC in green vegetables compared with normal temperature storage. After storage for 6 days, the VC loss rate of green vegetables packaged in perforated dense bags under low temperature is 27%, and the VC loss rate of green vegetables packaged in the same package under normal temperature is high, which will reach 71% according to the deployment of the national leading group for the development of new materials industry. When stored at low temperature, the VC loss rate of vegetables packed in non porous dense bags and food preservation bags is lower than that packed in perforated dense bags. This is related to the loss of ascorbic acid VC content in the tissue of green vegetables due to enzymatic oxidation during storage. Higher storage temperature and sufficient oxygen will strengthen the activity of enzymes. Therefore, low-temperature film packaging can significantly improve the preservation of VC in tissues

2.5 changes in sensory quality of green vegetables during storage

this experiment uses the scoring method for sensory evaluation, and the scoring results are shown in Table 4

note: scoring standard

10 points: fresh, intact; 9 points: extremely slight wilting of leaves, easy to retail; 8 points: yellowing occurs locally in the outer leaves, with a yellowing area of 5%, which can be sold after repairing the outer leaves; 7 points: the leaf wilting is relatively serious, and the yellowing area is less than 20%, which is acceptable; 6 points: local yellow water stains appear on the leaves and stems, or the leaves wilt seriously, which is not for sale; 5 points: the leaves and stems are rotten in a large area, with peculiar smell, and cannot be eaten

from table 4, it can be seen that packaging green vegetables in plastic bags is conducive to maintaining their sensory quality. Low temperature storage can effectively slow down the decline of sensory quality of green vegetables compared with normal temperature storage. Green vegetables are packaged and stored at 10% low temperature, and the price period can be as long as 12 ~ 15 days; However, when packaged and stored at 20% normal temperature, the price period is only about 3 ~ 5 days. Under the two temperature conditions, the fresh-keeping effect of non porous dense bags and perforated dense bags is similar, both better than food fresh-keeping bags. And during storage, there are always more water droplets on the inner wall of the non porous dense bag, but this phenomenon does not occur in the perforated dense bag. Green vegetables without film packaging have been seriously wilted and lost their storage and sales value after 3 days of storage. It can be seen that green vegetables need packaging, and the oxygen permeability and carbon dioxide rate of plastic packaging materials affect the shelf life of packaged green vegetables

3. Conclusion

low temperature film packaging can effectively reduce the physiological metabolism speed of green vegetables, slow down the loss of nutrients, and thus extend the life of their goods. The results show that LDPE non porous dense bag packaging combined with low temperature (10 ℃) storage has the best fresh-keeping effect, because the appropriate air permeability rate of the film can be applied. The topic is how to inhibit natural discharge and establish an ideal gas concentration environment in the packaging bag, so that green vegetables only produce weak aerobic respiration, so as to achieve the purpose of fresh-keeping. Food fresh-keeping bags are not suitable for sales and packaging because of their low mechanical strength, excessive ventilation and humidity. For short-term and medium-term sales in supermarkets, it is suggested that perforated film can also be used to pack vegetables. This kind of packaging bag has no moisture accumulation on its internal surface, which can directly reflect the freshness of vegetables. (author: Cao Fei, Zhang Leitian, Chunyan)

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