| To extend the storage period and maintain quality of fruits, people pay attention to find a simple, safe and efficient fresh-keeping method. The coating preservation technique is combined with biological preservation technique in this paper. A bioactive membrane containing active biocontrol yeast is made by sodium alginate, glycerol, plant growth regulators and Cryptococcus laurentii, then the membrane is applied to blueberries and sweet cherries preservation in order to come up with a natural, safe, and efficient material to keep fruits and vegetables fresh. The main findings are as follows:1.The preparation of sodium alginate composite membrane.Firstly,the main components of the composite membrane are screened by univariate experiments.The effects of different concentrations of sodium alginate,glycerol,plant growth regulators on the weight loss and decay index of blueberries are compared to determine the appropriate concentrations of the membrane.Then the L9(33)orthogonal experiments are designed to optimize the formulation of sodium alginate composite membranes according to the comparison of the tensile strength of the film, elongation at break and water vapor transmission.As a result,the best film-forming ratio is confirmed.Lastly.the microscopic structure of sodium alginate composit membrane is detected by DSC, FT-IR, X-RD and SEM.The results show that the components of the membrane have good compatibility.2.The preparation of bioactive membrane. The C.laurentii is added to the sodium alginate composite films containing different plant growth regulators to prepare bioactive membranes, then the films are dipping blueberries.By comparing the changes in weight loss, decay index and texture characteristics.the results show that the bioactive membrane containing methyl jasmonate has the best performance on reducing weight loss.decay index and maintaining texture properties, followed by the bioactive membrane containing salicylic acid. The components of the bioactive membrane are determined as follows:1.5% sodium alginate,0.3% glycerol,100μmol, L methyl jasmonate (or salicylic acid),109CFU/mLC.laurentii. At the same time, the influence of the membrane components on the growth of C.laurentii is studied,and the results show that the membrane liquid containing methyl jasmonate can promote yeast growth, while the membrane containing salicylic has no significant effects on the growth of C.laurentii.The microscopic structure of the bioactive membranes are characterized by DSC, FT-IR, X-RD and SEM. Compared to the sodium alginate composite membranes without antagonistic yeast, the thermal stability increases in the bioactive membranes, and the C.laurentii evenly distributes in the membrane solution.3.The two bioactive membranes containing methyl jasmonate or salicylic acid,sodium alginate membrane,sodium alginate membrane containing C.laurentii are dipping blueberries and sweet cherries.The results show that:(1)Regardless of storage of blueberries at a low or ambient temperature, the weight loss and decay index can be effectively controlled in coating groups,while the sugar content and titratable acid content can be maintained at a high level.The rate of generating anthcyanin slows down,and the firmness,springiness and cohesiveness are kept well. Meanwhile, the coating groups can inhibit MDA generation and improve SOD, POD and CAT activity, in which the bioactive membrane containing methyl jasmonate performs best on blueberries preservation at a low temperature.(2) The bioactivie membrane containing methyl jasmonate performs best in reducing weight loss and decay index during storage of sweet cherries.All the coating groups have no significant difference in controlling sugar and acid content changes.The bioactive membranes containing methyl jasmonate or salicylic acid can inhibit increasing anthocyanin content,maintain a high level of VC content,and delay the aging of sweet cherries. |
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