Preparation Of Flexible Polylactic Acid Film And Its Effect On Browning And Quality Of Fresh-Cut Asparagus Lettuce

Asparagus Lettuce is tasty,nutritious and popular with consumers.However,fresh-cut asparagus lettuce is susceptible to oxidize and browning,resulting in the reduction of its sensory quality and nutritional value.In order to inhibit the oxidative browning of fresh-cut asparagus lettuce,two types of membrane,PLLA/PBF and PLLA/PLBF,were prepared in this experiment by adding different ratios of polybutylene fumarate（PBF）and poly（lactic-co-butyl fumarate）（PLBF）on poly（lactic acid）（PLLA）as the base material.Select the film with the best overall performance for the storage and preservation of fresh-cut lettuce.The test results of PLLA/PBF blend membrane showed that the addition of PBF effectively improved the brittleness of PLLA film,and the maximum elongation at break of PLLA/PBF6 blend membrane was 159.3%.However,the compatibility between PBF and PLLA was poor.PLLA/PBF membrane is prone to crystallization during the process of film formation,resulting in reduced transparency of the film,which makes it unsuitable as a packaging material for fresh-cut asparagus lettuce.Compared with it,PLBF was compatible with PLLA,and the addition of PLBF improves the ductility of PLLA,the elongation at break of the blended film were more than 300%.With the increase of PLBF content,the O₂barrier of PLLA/PLBF gradually improved,and the O₂permeability of PLLA/PLBF blend membrane decreased to 113 cm³/（m²·d）,which was half of the O₂permeability of PLLA film in and more in line with the storage characteristics of fresh-cut asparagus lettuce.Based on the storage characteristics of fresh-cut asparagus lettuce,combined with the analysis of mechanical properties and O₂barrier properties of PLLA/PLBF membrane,it is concluded that PLLA/PLBF60 was the best ratio material.The results of freshness preservation experiments showed that compared with the CK and PE vacuum packing group,the PLLA and PLLA/PLBF60 vacuum packing groups effectively reduced the degree of browning of fresh-cut asparagus lettuce,inhibited the activity of polyphenol oxidase（PPO）,prevented microbial infestation,reduced water loss and oxidative decomposition of nutrients such as chlorophyll and Vc,among which the PLLA/PLBF60 group was more effective,and the sensory score of the PLLA/PLBF60group remained above 6.0 points at the 25th day of storage,and the browning index only increased by 14%.