Due to the safety, non-toxicity and biodegradability of chitosan in food coating preservation also attracted much attention from researchers. Chitosan is a natural preservative, easy to form a film, and the film has a certain selective osmotic effect on O2, CO2, C2H4, and has the function of moisturizing, can effectively make fruit dormancy, thus extending the freshness of fruit. Different fruits have different oxygen demand when breathing, and the resulting coating can have different permeability by changing the concentration of the spray. Therefore, it can be widely used in fruit and vegetable preservation.
In the preservation of pear, if coated with a layer of chitosan film on its surface, this storage method is better than 0℃ storage effect, can significantly extend the shelf life. Chitosan can also be used for tomato preservation. Tomatoes were coated with 2% chitosan. After 15 days of storage, it was found that the total acidity, total sugar content and vitamin C content of coated tomatoes were close to that of original tomatoes, and the storage effect was better than 0.2% sodium Benzoate solution.
Canada has developed a spray called "nutrient Saver" using chitin, which forms a thin film when sprayed on freshly picked fruit. Micropores in the film allow only the right amount of oxygen to pass through, effectively putting the fruit to sleep and thus extending its shelf life. Different fruits breathe different oxygen demand, can be changed by changing the concentration of chitin solution, and make it form a film with different permeability. General fruit can use chitin spray liquid preservation.
Gong Deqiang et al. studied the effect of chitosan coating treatment on the preservation effect of mango at room temperature (32±2℃) with "Yuxi No. 1" mango as the test material. The results showed that chitosan coating could significantly inhibit the color transformation of mango peel, reduce the occurrence of fruit decay and water loss, and maintain high fruit firmness and V-C content. At the same time, chitosan coating prevented the accumulation of soluble sugar and degradation of titratable acid, thus delaying the post-ripening process of mango, extending the storage life of mango and maintaining the original sweet and delicious flavor, among which 1.5% chitosan treatment had the best effect.
Yin Lian et al. used chitosan coating agent containing metal ions to keep grapes fresh. The results showed that Co2+ ion had the best effect, and the coating agent was low-cost, easy to operate, non-toxic and safe. Shen Dongfeng et al. studied the effects of different molecular weights and different concentrations of chitosan on the preservative effect of strawberry. The t test method was used to compare the antiseptic effect of strawberry. The chitosan with molecular weight of 10 ~ 100 000 was the most significant antiseptic effect at 2% concentration.
According to the study of Wu Qing et al., the harvested "Huaizhi" litchi was coated with chitosan or chitosan carrying the antioxidant V-C and the metal chelating agent EDTA on the fruit surface and placed at room temperature. The results showed that the coated litchi had better skin red, lower rotting fruit rate, lower weight loss and lower respiration rate than the uncoated litchi. Among them, the coated litchi containing 1%V -- C and 1% chitosan had the best effect, which could extend the shelf life of litchi to 3 days, more than 2 days longer than that of uncoated litchi.
Xu Qinghai et al. used chitosan as the coating agent to keep Nanguo pear fresh at room temperature. The results showed that the hardness and V-C content of Nanguo pear coated with 1.5% chitosan were close to that of fresh Nanguo pear, the weight loss rate and preservation effect were obviously better than that of the control group, and the Nanguo pear coated with 1.5% chitosan could be stored for more than 50 days at room temperature.
The study results of Chen Tian et al. on kiwifruit preserved by chitosan at room temperature showed that chitosan coating could significantly improve the freshness life of the fruit. The fruits were soaked in chitosan water solution for 30 seconds and dried in a ventilated place after removal. The next morning, the fruits were sealed and packed in polyethylene film bags and stored in corrugated boxes. The maximum storage period of blank samples at room temperature was 10-12 days, while the preservation period of chitosan water solution could be extended to 70-80 days.
The results of the study on the preservation of citrus with chitosan showed that the coating could effectively prevent the decline of V-C and the decrease of acid content and sugar content of citrus during storage, so as to achieve the effect of preservation.
Huang Xianghong et al. studied the preservation effect of chitosan film on grapefruit with four seasons, and the results showed that chitosan film could reduce the nutrient loss of grapefruit with four seasons, and 2.0% membrane had a better effect on inhibiting fruit respiration and reducing fruit decay.
The research results of Hua Shunan et al. on the preservation of bamboo shoots with chitosan coating showed that the coating agent made of 1.5% chitosan mixed with 1.0% p-hydroxybenzoate was coated at 50-60℃ and stored for 25 days at 4℃ and 95% relative humidity, which had a good preservation effect and could significantly inhibit the weight loss and the increase of cellulose content.
Chen Ningsheng treated cucumbers with 2.0% chitosan to keep them fresh for 20 days and green peppers for 25 days or longer. The experiment results of amaranth, leek and green vegetables showed that they had different degrees of preservation effect.
Soybean is a special high quality string bean variety in Heilongjiang province. Yang Xin et al. used 2% chitosan 0.2×10-5 sodium dehydrogenated acetate and 6-benzylaminopurine as a preservative to treat the soybean, and stored it at 12℃ with good fresh-keeping effect. Zhai Aihua et al. found that 2% chitosan combined with 50% aloe Vera extract can also have a good fresh-keeping effect when stored under the condition of pH5.7 and 0℃. Chitosan formed a thin film on the surface of the soybean, which slowed down the decomposition rate of chlorophyll, effectively prevented the water loss, significantly reduced the weight loss rate, and effectively reduced the V-C loss. The nutritional and sensory qualities of soybean treated with chitosan were good.
As people pay more and more attention to food safety, the research and development of natural preservative and preservative agents which can replace chemical compounds has become the current development trend. As a new kind of natural food preservation material, chitosan has been paid more and more attention because of its safety, bacteriological and film forming properties. On the basis of maintaining or improving the excellent properties of chitosan such as bacteriostatic and film forming, the chemical modification or modification of non-soluble chitosan, and the selection of appropriate natural antioxidants, metal salts and other synergizing ingredients for the combination, the development of fruits and vegetables with remarkable preservation effect, natural and safe compound preservative will have a huge market development potential.
(Note: This is the staff's reading and learning notes for sharing and communication only. This reading note was extracted from the book "chitooligosaccharides and Human Health", editor-in-chief: Feng Yanmin, published by Jilin University Press, the second edition, November 2019, ISBN 978-7-5601-3766-7. In the later stage, we will share the oligosaccharide knowledge notes we read regularly. Please pay attention to them. If there are forwarded references, please do not use them for commercial purposes.
Statement: The content of the above reproduced or quoted article is for study and research purposes only. If there is any discrepancy, correct it immediately.
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