Study On Preparation And Preservation Effect Of CS/γ-PGA Based Degradable Composite Plastic Wrap

In this study,chitosan（CS）,γ-polyglutamic acid（γ-PGA）,and curcumin（Cur）were used as raw materials for film-forming matrix,preservation agent,and antimicrobial agent,respectively,and the film was co-blended in the form of co-blending,and the free radical scavenging rate（DPPH）and the size of the diameter of the inhibition circle were used as evaluation indexes to explore the optimal preparation process and develop an optimal antimicrobial biological film based on the composite of CS/γ-PGA and Cur clings film.Finally,the structural changes in the relative abundance of microorganisms during the storage process of chilled beef treated with CS/γ-PGA-based biodegradable composite cling film was analyzed based on Illumina Nova Seq high-throughput sequencing technology.The results of the thesis are mainly for the application of CS,γ-PGA,and Cur in the preservation of chilled beef.The specific results are as follows:（1）Exploration of the optimal formulation of CS,γ-PGA,and CurBy exploring different concentrations of CS film,CS/γ-PGA composite film,and CS/Cur composite film,the concentration of each substance with better relative effect in the one-way test was determined by using the free radical scavenging rate（DPPH）and the diameter size of the inhibition circle as indicators.The results showed that chitosan concentrations of 1.4g/100 m L,1.5 g/100 m L,1.6 g/100 m L;γ-PGA concentrations of 3 g/100 m L,4 g/100 m L,5g/100 m L;and Cur concentrations of 0.20 g/100 m L,0.25 g/100 m L,0.30 g/100 m L were more effective.The three substances were co-mixed and blended separately,the optimal formulation was obtained as 1.5 g/100 m LCS+4 g/100 m Lγ-PGA+0.25 g/100 m L Cur.（2）Characteristics of the optimal CS/γ-PGA-based degradable composite cling filmThrough the characterization study of the optimal CS/γ-PGA-based degradable composite cling film,the addition of Cur resulted in a light-yellow color of the composite film,and the electron microscopy scanning microstructure showed that the composite film ofγ-PGA and Cur was more compact and smooth,and improved the rigidity of chitosan and enhanced the tensile strength up to 9.87±0.15 MPa.XRD light diffraction and FTIR spectroscopy showed that the interaction of CS,γ-PGA,and Cur when blended together,made the composite film more solid and compact inside,combined into a larger crystalline fraction,and its antibacterial performance was enhanced,and compared with a single chitosan film,the water vapor transmission rate was reduced to only 1.13×10^-10g/Pa*m*s,and the light transmission rate was only 36.54%.Moreover,the maximum thermal degradation rate of the composite film was higher than that of the chitosan film.Therefore,the composite film had improved characterization results in bacterial inhibition,antioxidant capacity,tensile strength water vapor transmission rate,and good bacterial inhibition effect,antioxidant capacity,and water vapor barrier.（3）Effect of optimal CS/γ-PGA/Cur composite cling film on physicochemical indexes of chilled beefAfter the composite cling film treatment,the chilled beef had a more balanced p H value.Whether it was compared with the blank group or the control group,the results indicated that the composite film effectively controlled the growth of microorganisms in the samples,and also inhibited the reproduction of some bacteria,thus effectively reducing the increase of TVB-N value,extending the expiration date and shelf life of the chilled beef for 7 days,and the loss of weight rate,sensory evaluation of the test group was higher than those of the blank group and the control group.（4）Analysis of structural changes in the bacterial flora of chilled beef treated with composite cling film by 16S r RNA high-throughput sequencingThe microflora’s structural changes and succession patterns in the samples during 1-7days were studied.The results showed that the structure and diversity of microbial flora changed significantly after being wrapped in CS/γ-PGA/Cur composite cling film.At the phylum level,under the storage condition of 4°C,the dominant bacterial phylum in the blank group started from the initial Proteobacteria and Firmicutes,and after a series of evolutions,finally became Bacteroidetes and Proteobacteria;while the dominant bacterial phylum in the control group gradually changed from Proteobacteria to Firmicutes and Bacteroidetes;the dominant bacterial phylum in the experimental group did not change significantly but still maintained an increase in the proportion of some unknown phyla.After genus-level analysis,it was found that in the three groups of chilled beef samples,the most dominant genus in the blank group was Ralstonia spp.on the first day,and it evolved to Fusobacterium spp.on the7th day.Over time,the initially dominant genus in group C was Ralstonia spp.which changed significantly from the original dominant genus to a more dominant flavor-like genus.Analysis of significant differences between groups by NMDS analysis,Anosim,and MRPP all showed that the intergroup differences between CPC and N groups were significant.This was followed by the intergroup difference between groups C and N.Finally,the intergroup difference between group CPC and group C was not so significant,but the intragroup difference was still relatively large.Therefore,it can be well demonstrated that the composite film can effectively inhibit the growth of microorganisms in chilled beef.