| With the increasing awareness of food safety and environmental protection,edible packaging,which is natural,safe and degradable,has become a hot research topic in the field of food packaging.Pectin is considered as a potential biopolymer for preparing edible films due to its wide range of sources,biodegradability and biocompatibility.Nicandra physaloides（L.）Gaertn seeds mucilage（NPG）accounts for about 15%of its seeds.NPG is mainly polysaccharide pectin material composed of galacturonic acid,which has some properties of high ester methoxy and low methoxy pectin,therefore,NPG is a promising material for preparing edible films.In this paper,the conditions of NPG extraction by ultrasonic-assisted hot water were optimized through response surface methodology.Then,NPG was used as the film forming substrate,and glycerol monolaurate（GML）was added as the antibacterial agent to prepare active films with good mechanical properties,barrier properties,antibacterial activity and degradability.Finally,the active solution of polysaccharide was applied to banana preservation experiment to explore its application effect in fruit and vegetable preservation.The main research contents and results are as follows:（1）The ultrasonic-assisted hot water extraction method was used to extract NPG,and the extraction conditions were optimized using response surface methodology.The optimal extraction parameters were that liquid-to-material ratio of 1:12 g/m L,ultrasonic time of 22min,and ultrasonic power of 2 W/g,the extraction rate of polysaccharide was 8.55%.The physicochemical properties and structure analysis showed that NPG was mainly composed of galacturonic acid（76.96%）,and its weight-average molecular weight was 444830 Da;The results of Fourier transform infrared spectroscopy showed that NPG had a characteristic absorption peak of polysaccharide,which was similar to commercial citrus pectin;X-ray diffraction showed that NPG had semi-crystalline and amorphous structure;Differential scanning calorimeter showed that the main weight loss peak of NPG was located at 236.2℃.The physicochemical properties and structure analysis indicated that the NPG was a novel pectin polysaccharide.（2）The NPG/GML antibacterial films were prepared by casting method.The effects of GML addition（0%,4%,8%,12%,16%）on the optical properties（color and transmittance）,microstructure,barrier properties,mechanical properties and antibacterial properties of the films were investigated.The results indicated that Nicandra physaloides（L.）Gaertn seeds mucilage based active films with 12%addition of GML led to stronger intermolecular interactions and more compact microstructure with good overall performance,whose tensile strength,elongation at break,water vapor permeability,oxygen permeability and carbon dioxide permeability were 35.48 MPa,8.38%,1.10×10-9g/m·s·Pa,2.81×10-15 kg·m-1·s-1·Pa-1,4.26×10-12 kg·m-1·s-1·Pa-1,respectively.In addition,the films also had excellent antibacterial activity,the inhibition rate of S.aureus and E.coli were 67.77%and 56.16%,respectively.The films had good degradability and could be completely degraded in 20 days.These results indicated that the appropriate addition of GML could enhance mechanical properties and barrier properties,and impart antibacterial activity to the film,which had a good application prospect in food packaging.（3）The NPG/GML active film solution was prepared for banana preservation,and the effects of the control group,NPG coating group,and the optimal GML addition coating group（NPG/GML coating group）on bananas preservation were compared.The results showed that the preservation effect was NPG/GML coating group>NPG coating group>control group during 10 days storage period.NPG/GML coating could effectively reduce the respiration rate and weight loss of bananas,maintain the fruit hardness,and effectively delay the rise of p H,total soluble solid and the decline of titrable acid.In addition,it also inhibited the rise of malonaldehyde content and polyphenol oxidase activity.The coating treatment could extend the storage period of postharvest bananas.The storage period of the control group was 4 days,the storage period of the NPG coating group was extended to 6 days,and the storage period of the NPG/GML coating group was extended to 8 days.The NPG/GML coating prepared in this experiment had good application effects in banana preservation. |
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