Preparation Of Chitosan Edible Membrane And The Effects On Preservation Of Blueberry

Blueberry, is also known as cranberries, its fruit which has strong antioxidantcapacity and anti-cancer effect is blue or red with delicate flesh, small grains, sweetand sour taste and refreshing aroma. There are Vitamin C, anthocyanins, flavonoids,Vitamin E and superoxide dismutase (SOD) and other nutrients in the peel and pulp ofthe blueberry, it is known as "The King Fruit of The World”. Regarded the as one ofthe top five healthful food of humans, blueberry is with broad prospects ofdevelopment and application.However, as berry, the storage period of fresh blueberry is very short. If nottreated timely after picked, it would soon become flexible or decay, a variety ofnutrients such as Vc decline quickly, the flavor fades gradually, which brought hugeloss to the blueberry industry. Therefore, how to prolong the shelf life of freshblueberry is one of the problems to be solved urgently in the blueberry industry.In this study, chitosan with high deacetylation degree, lactic acid and gelatin areselected as the main materials of membrane. Chitosan and lactic acid haveantibacterial function, gelatin has superior mechanical properties. Consolidating threeadvantages, an edible film which was used in fresh blueberry preservation wasprepared. With the water vapor permeability (WVP), tensile strength, breakingelongation as measured indicators, the most suitable composition membrane solutionwas optimized by single factor experiments and orthogonal experiments (L934). Theeffect of salicylic acid on the mechanical properties of composite membrane was alsoresearched. Meanwhile, the chitosan composite membrane was applied to freshblueberry as well, the fresh-keeping effects and preservation mechanism were studiedin order to meet the needs of the factory producing. The main study results are asfollows:(1)Using the edible composite film liquid as the research object, the influence ofthe concentration of chitosan, lactic acid, gelatin, glycerin on water vapor permeability, tensile strength and breaking elongation was determined; the bestchitosan composite membrane group was optimized through single factor experimentand orthogonal experiment (L934), the optimum chitosan composite membraneconcentration (%) was divided into: chitosan1, lactic acid1.2, gelatin1.5, glycerin0.2. This group that is with lower water vapor permeability (WVP), appropriatetensile strength and breaking elongation, may reduce the gas exchange inside andoutside of the blueberry peel, ensure that composite membrane can still maintain thestructure itself under certain pressure and the friction.(2) To research the preservation effects of the optimum chitosan compositemembrane on fresh blueberry and the fresh-keeping results of alicylic acid anddifferent chitosan concentration, the blueberry was treated by using optimalmembrane with changed chitosan concentration mixed with0.5mmol/L salicylic acidsolution, the physiological changes of the blueberry at room temperature and lowtemperature conditions were investigated, the preservation results were as follows:(a)Under the room temperature and the low temperature storage conditions, coatingtreatment could reduce the decay rate and weight loss rate of fresh blueberry, chitosan+salicylic acid composite membrane was relatively best in all, coating groups and thecontrol group were significantly different;(b) Under the low temperature condition,every coating group could effectively reduce the decline of hardness, titratable acidand Vc content of blueberry, maintained the stability of the total sugar andanthocyanin content,1%chitosan+salic ylic acid composite membrane worked best.From the actual sales perspective, in20d storage at low temperature, the coatinggroups could hold more5~7shelf life days than control group, and could ensure thetaste, flavor and nutritional value of blueberry better; in6d storage at roomtemperature, it could prolong1~2shelf life days.(3) Through the preliminary inquiry on preservation mechanism of the chitosancomposite membranes working on fresh blueberry, the results showed that: everycoating group could effectively inhibit the respiratory intensity of fresh blueberry,reduce respiratory consumption and the ethylene emission, maintain higher SOD,POD, CAT activity, decrease the production of MDA, delay the ripening and senescing process of blueberry, extend its shelf life. The effect of1%chitosan+salicylic acid composite membrane on blueberry preservation was the most obvious inall.