Study On The Preservation Effect Of Microwave Combined With Plant Essential Oil On Fresh-Cut Broccoli

Broccoli?brassica oleraceaL.var.italica?was rich in nutrition.It was the cell rupture,browning,flower yellowing,lossed of nutrients,decreased resistance to microorganisms and other quality problems that reduce the shelf-life after fresh-cut treatment.In this paper,'dongzhilv'broccoli was used as the test material.It studyed the isolation,identification of pathogens and plant essential oils inhibitory effect on pathogens.The effect of microwave combined with plant essential oil on the preservation of fresh-cut broccoli and the analysis of essential oil residues were studied in order to provide some evidences for the application of microwave and plant essential oil to freshly cut broccoli.The results were as follows:In this work,the pathogenic fungi strain AB01 was isolated and purified.Besides,the AB01 was subjected to pathogenic test.The phylogenetic tree was constructed based on the pathogen internal transcribed spacer?ITS?of the AB01,and the pathogen AB01 was identified as Alternaria alternata.Antibacterial effects toward AB01 of six kinds of essential oils including cinnamon,fennel,bovine,clove,thyme and citronella were tested in both vitro and vitro in order to select the optimum oil species and concentration.The results showed that cinnamon essential oil possessed best antibacterial effect toward AB01,and the MIC and MFC were 0.05?L/mL and 0.15?L/mL respectively.The fennel and oregano were also effective.In this paper,11 traits of the effect of cinnamon,oregano,fennel oil on quality of fresh-cutting broccoli were analyzed by principal component analysis?PCA?method.An assessment model was established to screen the best essential oil treatment.3 principal components were screened out through principal component analysis which accounted for86.462%of the total variance.The results showed that the quality score of fresh cut broccoli treated with different essential oils was the highest?0.34?in the cinnamon group as to effectively delay the decline of chlorophyll,vitamin C,maintain a high level of total phenol and total flavonoids.Thus,cinnamon oil was conductive to fresh-cutting broccoli preservation.The results showed that proper microwave treatment?group A to D?can passivate the activity of peroxidase enzyme,delay the abatement of vitamin C?Vc?,chlorophyll and water content.It also can keep higher content of total phenolic and total flavonoids during storage.Microwave treatment with 300 W for 40 s kept the best freshness retaining in this experiment after that brocoli could store at?4±0.5??for 10 days which was the same as results of PCA.The contents of Vc and chlorophyll were 62.76 mg/100 g and 0.22 mg/g,respectively the group B?300 W,40 s?was significantly better than blank group.Microwave combined with cinnamon essential oil compound treatment can effectively delay the shelf-life of fresh-cut broccoli decline because the compound treatment group had the highest score during storage which was significantly better than the control group.At the same time,the relative content of aldehyde decreased from 29.49%to 3.62%.The relative content of cinnamaldehyde had a certain relationship with the odor score.Within a certain range?3.62%-23.13%?,the odor score had a positive correlation with the relative content of cinnamaldehyde,indicating that cinnamaldehyde could delay the decrease of the odor score of broccoli to a certain extent.Based on predictive microbiology theory,the kinetics models of the total number of colony had been set up by modified Gompertz equation and the relationship between temperature and C?maximum specific growth rate?,t?lag time?was discussed combined with Belehradek equation.Finally,the shelf-life prediction model of fresh-cut broccoli was developed,followed by an accuracy assessment of the shelf-life prediction model.The result indicated that the growth cruves of the total number of colony on fresh-cut broccoli at above 4 temperatures could be well described by the modified Gompertz equation?R²>0.95?.It was observed that C increased with increasing temperature while t decreased with increasing temperature.The temperature dependence of C and t was modeled using Belehradek equation,and the linear relationship between T?temperature?and C^0.5?(t^-1)^0.5could be well described by the correlation regression showed.The parameters of the the shelf-life prediction model of fresh-cut broccoli were:B=7.88 lg?CFU/g?,N=6.72lg?CFU/g?,a=0.0518,b=0.685,c=0.0959,d=0.7077.Validation of built shelf-life prediction model was preferred by comparing with experimental development of the total number of colony grown on fresh-cut broccoli at 5?.It showed from the accuracy assessment between predicted and observed shelf-life that relative error was-12.20%calculated by the shelf-life prediction model of fresh-cut broccoli?SL?.The results derived from validation showed that the shelf life of fresh-cut broccoli with microwave with essential oils treatment from 0 to 30?could be predicted availably by the shelf-life prediction model?SL?built in our research.