The Inhibitory Of Eugenol Against Alternaria Sp. And Its Application In Blueberry Preservation

Blueberries are sweet,dsour,and rich in nutrition.They are new economical small berries with high economic values and development prospects.However,the blueberry fruit is soft and the peel is thin,it is hot and rainy at the time of picking.In addition to mechanical damage,the fruit pedicle is prone to scars,and it is extremely susceptible to microbial infection and rots,which brings great losses to the blueberry industry.In this paper,"brilliant" blueberry fruits(collected from Baima Town,Lishui District,Nanjing City)were used as research objects.Isolation and identification of bacteria that caused its decay and spoilage under natural conditions and identification of dominant spoilage bacteria were investigated.The effect of growth and fresh-keeping effect of blueberries;by studying the mechanism of eugenol's inhibition of Alternaria sp.And the freshkeeping effect of blueberries,we hope to provide a theoretical reference for the development of green,healthy and convenient fresh-keeping methods.The main research contents are as follows:(1)Eleven spoilage fungi were isolated from rotten blueberries by tissue isolation.According to the colony characteristics and molecular biological information of the strains on the PDA,the 11 strains belonged to 6 genera,namely Nigeria oryzae,Penicillium sp.,Cladosporium sp.,Alternaria sp.,Hanseniaspora uvarum and Metschnikowia pulcherrima.Pathogenicity tests confirmed that Alternaria sp.was the main spoilage bacterium in blueberry harvest.(2)Using the colony diameter and decay rate as indicators,the effects of different cold sterilization techniques on the growth of Alternaria sp.and the fresh-keeping effect of blueberries were evaluated.The results showed that the biological preservatives,cold plasma and high-power pulsed microwave could inhibit the growth of Alternaria sp.to a certain extent,of which eugenol had the most significant inhibition effect(P <0.05),with a diameter of only 32.90 mm.After eugenol,cold plasma and high-power pulse microwave treatment of blueberries,the decay rates decreased by 31.25%,25.00% and 18.75%compared with the control group,respectively.(3)Using Alternaria sp.as the test bacteria,the effects of eugenol on the growth of Alternaria sp.Mycelium,spore germination,cell membrane and cell wall were studied.The results showed that the concentration of eugenol at 0.30 mg/m L could completely inhibit the growth and spore germination of Alternaria sp.;Alternaria sp.treated with 0.30 mg/m L eugenol showed severe deformation of the cells,a large number of wrinkles on the surface,loss of intracellular substances,no complete organelles by scanning electron microscopy(SEM)and transmission electron microscopy(TEM)observations.Propidium iodide(PI)staining showed red fluorescence,and the extracellular soluble protein content and electrical conductivity increased by 1.18 and 8.02 times,respectively.The activities of plastase and ?-1,3-glucanase increased by 70.37% and 33.33%,respectively.Eugenol mainly destroys the cell wall of Alternaria alternata,changes the permeability of the cell membrane,and then inhibits the growth,metabolism and reproduction of Alternaria sp.,thereby exerting antibacterial activity.(4)Blueberry was used as a test material to study the effect of eugenol on postharvest preservation.Eugenol with the concentrations of 0,2,4,6,8,and 10 ?L/L,respectively,was used to fumigate blueberries,and the relevant indicators were periodically tested.The results showed that eugenol fumigation could effectively reduce the rot rate of blueberries,especially when the fumigation concentration was 8 ?L/L.Compared with the control group,8 ?L/L eugenol fumigation could reduce the number of microorganisms on the fruit surface during storage,delay the blueberry rot for 2?3 days,and reduce the decay rate by 7.50% when stored for 10 days.The titrated acid and soluble solids content were 0.20% and 0.23% more,respectively,and the anthocyanin content was 0.28 mg/g more.Total phenols and flavonoids peaked.In general,nutritional quality of the blueberries with eugenol fumigation was better maintained.After ten days of storage,the enzyme activities of polyphenol oxidase,superoxide dismutase,peroxidase,and catalase in blueberries were increased 82.71%,33.94%,23.68%,and 50.57%,respectively,compared to the control group,and malondialdehyde content was effectively suppressed.The results in this study showed that eugenol fumigation treatment has a certain preservative effect on blueberries.