| In recent years,people are becoming more and more strict with food packaging,and the consciousness of hygienic environment is also increasing.Therefore,the bio matrix packaging material instead of plastic packaging has been widely concerned and researched.Biobased packaging material is a kind of edible film material with natural active ingredients that extends the shelf life of food,such as protein,polysaccharides and lipids.Chitosan and apple pectin are edible polysaccharides,which are often used in fresh-keeping materials.However,the physicochemical properties,such as the antioxidant properties and mechanical properties,of the edible film formed by a single polysaccharide need to be improved.Studies have shown that natural active ingredients extracted from plants and animals,such as essential oils,phenols,and gelatin,can enhance the physicochemical properties of edible films.China is a big country of apple-planting in the world.In the past few years,the output of apple is in the forefront,and the market resources are abundant,which will produce a large amount of waste of resources.Therefore,it is particularly important to improve the effective utilization of resources.Apple is rich in phenols,and its extracts are applied to edible films,which not only achieves the comprehensive utilization of resources,but also increases the economic benefits,and broadens the application field of polyphenols.Walnut is a kind of nut with high functional value,which is rich in polyunsaturated fatty acids,such as linolenic acid,linoleic acid,oleic acid and so on.But improper storage after harvest can lead to the moldy deterioration of walnut,the oxidation of fatty acid,and affect the sensory quality of walnut kernel Walnut is mainly stored by physical method with large cost and difficult equipment maintenance technology.In this study,apple polyphenols were added to chitosan and pectin respectively to prepare composite membrane fluid.Rheological properties,oxidation resistance and thermal stability were researched.And using electronic nose to control the quality of coated walnut during different storage time,intended to provide scientific and theoretical basis of application of apple polyphenols to composite membrane fluid.Contents and main results as follows:1.11 kinds of polyphenols in apple were detected by HPLC method,which accounted for 68.6%of the total amount of the sample,indicating that apple polyphenols had high purity.The content of phlorizin,ellagic acid and procyanidin B2,were 21.22 ±0.79%,10.11 ±0.24%and 9.29 ± 0.05%,respectively.The results of antioxidant test showed that apple polyphenols had good free radical scavenging ability and coukl effectively inhibit lipid oxidation.2.A composite membrane fluid was prepared with 5%(w/v)chitosan solution and polyphenols as raw materials.The addition of apple polyphenols can significantly improve the antioxidant activities of the chitosan membrane liquid(P<0.01).The increase of apple polyphenols concentrations can lead to the increased antioxidant ability of the composite membrane liquids.When the apple polyphenols addition was 0.5%,the DPPH scavenging rate,inhibition capacity of lipid oxidation and OH radical scavenging rate were determined to be 41.33%,56.32%,35.44%,respectively.As the addition amount of apple polyphenols was increased to 1.5%,the antioxidant ability of the composite membrane liquids increased to 94.3%,95.9%,98.4%,respectively,significantly higher than that of 0.5%polyphenol-incorporated composite membrane liquid(P<0.01).Compared to the BHT(1.5%),antioxidation properties of the composite membrane liquids with 1.5%apple polyphenols were higher(P<0.01).Moreover,the rheological analyses suggested that the composite membrane liquid is non-Newton pseudoplastic liquid(n<1,R2>0.99).With the increase of shear rate,the viscosity of the composite membrane liquids displayed an initially decrease but then a relatively stable trend(approximately 5Pa·s).Meanwhile,the incorporation of apple polyphenols enhanced the viscoelastic property of the composite membrane liquids.Dynamic rheology of the composite membrane liquid transformed from G'<G" into G'>G".The results of FTIR and X-ray showed that the intermolecular interactions of apple polyphenols(-OH)and chitosan(-OH,-NH2)were formed,resulting in the slight change of absorption peak of the composite membrane at 3400cm-1,1545cm-1 and 1245cm-1 and resulting in the reduced crystallinity of chitosan.According to the result of thermal analysis,thermal stability of the composite membrane liquids increased,probably due to the hydrogen bonds formed via the linkages between apple polyphenols and chitosan.3.The edible coating was made up of 5%apple pectin solution as the substrate and apple polyphenol with different concentration as the additive.The effects of the addition of apple polyphenol on the rheological properties and antioxidant activities of the edible coating were investigated.The results suggested that the control(pectin solution)and the mixture liquids all exhibited a shear-thinning behavior,indicating that they are typically non-Newtonian fluids.The increase of polyphenol addition amounts caused the significant increase of viscosity of the liquids;when the polyphenol concentration was increased to 1.0%,the viscosity reached to approximately 220 Pa,significantly higher than the control(108 Pa).Moreover,as the polyphenol addition increased,the antioxidant activities of the mixture liquids including the inhibition capacity against lipid oxidation,DPPH scavenging capacity and total reducing capability,were significantly enhanced.At 1.0%of the polyphenol concentration,the prepared mixture liquid had a higher antioxidant activity than that of BHT.However,after the polyphenol concentration was increased to 1.0%,the continuous increase of the polyphenol concentration did not lead to significant enhancement of the viscosity and antioxidant activity of the mixture liquid.In conclusion,A high viscous mixture liquid can be obtained by adding 1.0%polyphenol into 5%pectin solution,and the resulting liquid can be used as a potential edible coating material in food preservation due to its good antioxidant activities.4.Using the response surface method established the optimum processing parameters:soaking time(17.73h),the concentration of alkali solution(1.36%),and the alkali perm time(116.67s).The effect of compound membrane solution on the preservation of walnut kernel was detected by electronic nose.The results showed that with the prolongation of storage time,the volatile substance in walnut kernel was produced,such as pyrazine and pyrrole,which caused the increase of response value of electronic nose sensor.In addition,apple polyphenols can reduce the production of oxygen compounds and coating processing can retain the aroma components of walnut kernel and prevent volatilization.PCA and LDA were used to effectively distinguish walnut kernel with different storage time,indicating that there were significant differences in walnut kernel with different storage time.A sensory evaluation system for coated walnut kernel was established based on fuzzy mathematics and principal component analysis,in order to provide a more intuitive,scientific and credible evaluation system for food sensory evaluation. |
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