| In this paper, fresh-keeping coating technique and coating combined MA (Modified Atomosphere) technique are used to preserve blueberry which is hard to retain freshness. The fresh keeping effects of different preservative treatments for blueberry are evaluated by a large amount of experiments. The results of the experiments could be good references for the improvement of current blueberry fresh-keeping and logistics and could be beneficial to provide theoretical basis for other fruits and vegetables fresh-keeping.(1) Both chitosan film and burdock-modified chitosan film were prepared. The structure and composite were studied by SEM and FTIR. Results showed that good compatibility and crystallization of the burdock-modified chitosan film could be achieved by 0.10g/ml burdock extract and 0.02g/ml chitosan. The film exhibited good hydrophilia and the contact angle of this film decreased. The tensile strength of the film came to 51.76Mpa and its breaking elongation rate reached to more than 40%. The water vapor transmission rate of this film was 5.01mg·m/(h·m·kPa) (the minimum) and the O2 and CO2 transmission coefficient were 0.11 and 0.38n·m/h·m2·Pa respectively. The free radical scavenging rate reached to 80% and bacteria inhibitive rate reached to 100%. By adding glycerol and gelatin into the composite membrane, the optimum proportion of the film was:chitosan-0.02g/mL, burdock extract-0.1 g/mL, the gelatin-0.03g/mL and the volume fraction of glycerol -0.5%.(2) The chitosan membrane, burdock extract film and the burdock-modified chitosan film with optimum proportion were respectively used to the blueberry for fresh-keeping and the results showed:the above three membranes could keep the blueberry fresh for a certain time. When the concentration of chitosan membrane was 0.02-0.025g/mL and the mass concentration of burdock extract was in the range of 0.08-0.10g/mL at room temperature, good fresh-keeping effects on the blueberry could be obtained. The blueberry could be stored for lOdays. Notably, the blend membrane could increase the storage life of the blueberry to 12 days at room temperature, with 3-6 days longer than that of control group. The decay rate, hardness, respiratory intensity, anthocyanin content, MDA content, titratable acid content, peroxidase activity and VC content had significant difference compared with the control group (P<0.01).(3) In modified atmosphere experiments, the film with optimum proportion was used to blueberry preservation. Based on the weightlessness rate, soluble solids content and anthocyanin content index, orthogonal test optimization, the best gas packaging composition should be O2:6%, CO2:10%, N2:84%. By testing the physiological index of blueberry, it could be concluded that coating combined with modified atmosphere had better effect on blueberry fresh-keeping. It could effectively inhibit the changes of each index and the storage period could be extended to 20 days. According to the experimental data, it could be concluded the coating preservation technique and modified atmosphere packaging had different preservation mechanism on blueberry. The coating preservation had greatly influence on blueberry quality owing to its antioxidant and antimicrobial activity while the modified atmosphere packaging could reduce the decomposition of nutrients owing to the inhibition of respiration and evaporation. Because the modified atmosphere packaging created a relatively closed environment for blueberry, it could lead to less water evaporation and improve the quality and sales value of the blueberry.(4) Finally, six different fresh-keeping methods were used to simulate the blueberry logistics. The TPA parameters at different times of the logistics process were tested and the change tendency of shelf blueberry textural index was researched during six days after the end of logistic. It was found that in the logistic simulation, all the TPA parameters of the blueberry were higher than the other groups with precooling+coating+MAP. During the shelf life, all the blueberry textural indexes had a slightly downward trend. When the shelf life extended to 18 days, the TPA parameters changed 20%. The fresh-keeping time was 10 days longer than the other groups, which was twice the storage life to the other methods. Therefore, it could ensure the logistics links of the blueberry and significantly increase its shelf life by packaging the blueberry with the fresh-keeping method of precooling+coating+MAP, which can guarantee the shelf sales period is extended to 18d. |
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