Study On The Effect Of Tea Leaf Extract Combined With Chitosan On Postharvest Diseases Resistance Of Apple

A series of physiological changes such as hardness decline and decomposition of nutrients will occur during postharvest storage of apple.After long-term storage,not only the quality of apples drops rapidly,but also the decay loss will be aggravated due to the action of microorganisms,which will seriously affect the commodity value and greatly reduce the economic benefits.In order to explore the inhibitory effect of the compound treatment of tea leaf extract and chitosan on the main postharvest diseases of apple and the effect of storage resistance,this study that the compound combination with the best antibacterial effect was screened through the antibacterial test firstly.Using red Fuji apple as the material,the fruit was immersed in the mixture,chitosan and pure water for 10 s and then inoculated with Penicilliosis.expansum or Botrytis.cinerea after 24 h.The disease resistance indicators were measured by sampling regularly.At the same time,the fruits treated with the combination agent,chitosan and pure water were placed in a refrigerator for storage.Then the related indicators of fruit quality and antioxidant capacity were measured through regular sampling.The main research results are as follows:1.The main components of tea leaf extract were tea polyphenols,caffeine and theobromine at the concentrations of 0.250,0.104 and 0.069 mg/m L respectively.Tea leaf extract can inhibit the growth of postharvest pathogens.The single factor test showed that the antibacterial rates of 100%and 75%tea leaf extracts were higher than 2%chitosan,the antibacterial rate of 50%tea leaf extract was similar to 2%chitosan,and the antibacterial rate of 25%tea leaf extract was similar to 0.5%chitosan.The optimum combination was100%tea leaf extract mixed with 1.5%chitosan through bacteriostatic test.The optimum combination treatment group could damage the hypha,inhibit spore germination and bud tube elongation.The optimal combination made the hypha surface uneven,with obvious cracks and wounds,and exposed the internal outline of hypha.The chitosan treatment group only slightly deformed the hyphae,and there was no significant damage trace in the CK group.2.The best compound agent treatment can improve the disease resistance of red Fuji apple.The best combination could significantly increase the chitinase andβ-1,3-glucanase activities of fruit,reach the peak of activity and show significant differences at 2 d and 3 d respectively.It could increase the sensitivity of phenylalanine ammonia-lyase,and the activity of cinnamic acid-4-hydroxylase significantly.The total phenol and flavonoid contents could be accumulated more quickly to a higher level,and the lignin content was higher than those in the chitosan treatment group and the CK group.The compound agent could obviously inhibit the growth of blue mold and gray mold disease spot and show the difference after being inoculated for 3 days.3.The best compound agent treatment can delay the quality decline of red Fuji apple.The color of the compound treatment group was darker than that of the chitosan treatment group and the CK group at 0-60 d storage,and the color saturation was not significantly affected.At the end of the storage period,the hardness of the compound treatment group,the chitosan treatment group and the CK group decreased by 1.25,1.58 and 1.70 kg·cm^-2respectively,and the titratable acid decreased by 0.353,0.375 and 0.402%respectively.The treatment with that compound agent delayed the conversion of soluble solids.The peak values of respiratory intensity and ethylene release rate in the chitosan treatment group and the combination treatment group were delayed.The best combination treatment could enhance the antioxidant capacity of red Fuji apple and prolong the fruit storage period.The antioxidant enzyme activities were significantly increased in the compound treatment group.The glutathione and ascorbic acid contents in the combination treatment group remained the highest among the three groups when the storage time was longer than 90 d.After the treatment with the compound agent,the content of total phenols reached the maximum after60 d of storage,the content of flavonoids reached the maximum after 75 d of storage,and malondialdehyde always maintained the minimum content.After the storage,the weight loss rate and diseased fruit rate of the combination treatment group and the chitosan treatment group were significantly decreased.To sum up,on the one hand,tea leaf extract compounded with 1.5%chitosan can inhibit the activity of pathogenic bacteria,improve the activity of self-resistant enzymes and the content of resistant substances in fruits,so as to achieve the inhibition of postharvest diseases.On the other hand,it can delay the decline of fruit quality,improve the activity of antioxidant enzymes and the content of related substances,so as to extend the storage period of fruits.