Study On The Application Of Cold Plasma Technology In The Preservation Of Daylilies

Fresh daylily has a crisp,fresh and sweet taste,rich nutrition,and contains sugar,protein,vitamins and a variety of essential amino acids.It is a treasure in the dishes.However,it is easy to lose water,of poor storability,easy to rot after harvest and affects its shelf life.Therefore,choosing an appropriate preservation method to slow down the postharvest physiological activities of daylily and prolong its shelf life has become an urgent problem to be solved.And for that,this topic takes Ningxia daylily as the research object to explore the effect of cold plasma treatment on the daylily.The main contents and results are as follows:Different packaging methods have great differences in the preservation effect of daylily.The effects of PE packing,PVC packing and PP packing on the quality of fresh daylilies were studied by measuring the physical and chemical indexes and evaluating the sensory quality during storage.The results show that the most suitable packaging for daylily is PE,followed by PVC.The increase in weight loss rate and a*value of PE packaging was significantly lower than that of PVC packaging and PP packaging(P<0.05),VC content,soluble protein,soluble solid content and good flowers rate were significantly higher than that of PP packaging(P<0.05).Combined with the sensory evaluation scores of appearance,PE packaging was more suitable for postharvest packaging and storage of daylily than the other two packages.By changing the discharge voltage,discharge frequency and discharge time,the optimal processing conditions of PE packaged fresh daylilies were studied by low temperature plasma equipment.First,the principal component analysis method and the comprehensive scoring method of membership degree were used to determine the weight of each quality index of daylily.The total number of colonies was 0.39,the sensory evaluation was 0.38,the VC content was 0.06,and the peroxidase(POD)activity was 0.17;Based on the single factor test results,using the Box-Behnken response surface method,and taking the daylily comprehensive evaluation value as the response value,the optimal process conditions for the cold plasma treatment was predicted by the quadratic regression model,the discharge voltage was 125.42 kv,the discharge the frequency was 119.35Hz,the processing time was 130.62s,and the comprehensive evaluation value of daylily was 0.794.Under these conditions,the comprehensive evaluation value of daylily was 0.786,which showed that the process optimization was scientific and reasonable.The cold plasma equipment was used to treat fresh daylily at 125kv and 120Hz for 130s,and the effect of cold plasma treatment on the active oxygen metabolism and quality of postharvest daylily was explored.The results showed that low-temperature plasma can induce SOD activity in fresh daylily,significantly increase CAT and POD activity(P<0.05),inhibit the accumulation of hydrogen peroxide,significantly inhibit the accumulation of malondialdehyde content(P<0.01),and significantly delay the increase of cell membrane permeation(P<0.05)and the hydrolysis of daylily soluble protein,maintain the soluble solid content of daylily,significantly delay the decrease of VC content and the increase of the a*value of daylily in the late storage period,delay the browning of daylily.Combined with LF-NMR research results show that the treatment group daylily showed strong water holding capacity and freshness.Transmission electron microscopy observation results showed that cold plasma treatment had no significant effect on the mesophyll cell structure of daylily.The changes in physiological and biochemical quality of daylily after packaging under different storage and circulation temperatures after cold plasma treatment were studied,and a shelf life prediction model was established based on quality indicators.The results showed that the changes in weight loss rate,malondialdehyde content,and chromaticity value can be used as key quality factors for the model establishment The established kinetic model and the Arrhenius equation fitting coefficient R2 average value are above 0.90,and the shelf life prediction model can accurately predict the deterioration of quality and the remaining shelf life in the temperature range of 4℃～30℃after harvest.The shelf life model based on malondialdehyde content has the highest prediction accuracy.