Application Of Layer By Layer Self-assembled Edible Coating In Preservation Of Blueberries At Room Temperature

Blueberry(Vaccinium of Ericaceae),scientific name bilberry,bilberry plant of Rhododendron family,contains important nutrients such as vitamins,anthocyanins and antioxidant enzymes,so it is considered to be the most abundant dietary antioxidant and health-promoting bioactive compounds one of the sources.Because of its seasonal growth and short edible cycle,blueberries are easy to lose water and rot after harvest,and are not easy to store.In order to improve the edible value and commercial value of postharvest blueberries,the layer-by-layer(LBL)edible coating method was used to construct the coating film,and the changes of the physicochemical indexes and antioxidant indexes of blueberries were detected,so as to achieve the goal of keeping blueberries fresh.Maintaining the quality of blueberries during the storage period and extending the shelf life of blueberries provides a fresh-keeping method,thereby improving the fresh food market time of blueberries,thereby promoting the economic development of the fruit and vegetable market.The main conclusions obtained are as follows:(1)Study the optimal construction process of layer-by-layer self-assembled edible coatings.Using "emerald" blueberry as the test raw material,the coating conditions of layer-by-layer self-assembled fresh-keeping blueberry were explored through single factor experiment and orthogonal experiment.The optimal parameters are that the concentration of chitosan(CS)is 6 mg/m L,the concentration of sodium carboxymethyl cellulose(CMC-Na)is 10 mg/m L,and the concentration of glycerol is0.06 ml/m L.The soaking sequence of soaking in cellulose sodium and then soaking in chitosan solution,and the drying time between soaking is 40 min.The resulting LBL edible coating can extend the shelf life of blueberries by 6 days.On the 12 th day,the weight loss rate of blueberries was(23.97 ± 2.64)%,and the ratio of sugar to acid was(17.96 ± 0.12)%.All are greater than 20 %,belonged to an imbalanced state.(2)To study the changing laws of physical and chemical indexes of blueberries under different coating treatments.The LBL method was used to construct an edible coating on the surface of blueberries(LBL group),and compared with the control group without any treatment(CK group),the single-layer carboxymethyl cellulose sodium coating group(CMC-Na group),and the monolayer The fresh-keeping effect of chitosan coating group(CS group)on blueberries.The changes of typical physical and chemical indexes of blueberries during storage(12 days)were determined.The results showed that the weight loss rate,rot rate,sugar-acid ratio,respiration rate,cell membrane permeability,water distribution and microbial content of blueberries were better than other treatment groups in LBL treatment.For example,the cell membrane permeability of blueberries treated with LBL coating was(62.49 ± 9.08)% on the12 th day,which was significantly lower than that of the CK group(80.71 ± 16.95)%,the CMC-Na group(70.29 ± 18.76)% and the CS group(66.98 ± 9.32)%(p < 0.05).Moreover,during the storage period of 12 days,the production of mold and bacteria was not detected in the LBL group.(3)To study the changes in antioxidant indexes of blueberries under different coating treatments.The typical antioxidant indexes of LBL group,CK group,CMC-Na group and CS group were compared during the storage period of blueberries.The results showed that the LBL treatment group had better DPPH· clearance rate,·OH clearance rate,PPO enzyme activity,POD enzyme activity,CAT enzyme activity and other indicators to blueberry than other treatment groups.For example,the PPO enzyme activity clearance rate of blueberries treated with LBL coating was(1.66 ± 0.24)U/g on the 12 th day,which was significantly lower than that of the CK group(5.80 ± 0.89)U/g(p < 0.05).