Study On The Effect Of CMC-Na/PVA Composite Aerogel Loaded With Essential Oil On The Preservation Of Three Kinds Of Southern Fruits

In recent years,the fruit industry is developing rapidly.However,serious economic losses have been caused due to the relatively concentrated time of fruit production,the loss of water,and the infection of pathogenic fungus.The potential dangers of using traditional chemical fungicides during fruit storage have attracted public attention and it is necessary to develop and apply new preservation techniques.Essential oils are considered as the best substitute for chemical preservatives because of their natural,safety,green,antifungal and antioxidant abilities.However,due to the defects of essential oils such as poor stability,insoluble in water,volatile characteristics,and damage the fruit epidermis under highconcentration treatment,which limits their application in the preservation of fruits and vegetables.Aerogels have abundant pore sizes and strong adsorption properties,making them ideal materials as carriers of essential oils.In this paper,composite aerogels were prepared using sodium carboxymethyl cellulose(CMC-Na)as the substrate and polyvinyl alcohol(PVA)as the hydrophobic enhancer,then their structures were characterized and analyzed.The sustained-release properties and antifungal and antioxidant activities of the above materials loaded with essential oils were investigated,and applied to citrus,strawberry and pitaya for postharvest preservation,measuring the changes of physiological and biochemical indexes before and after the treatment of essential oils during storage,which can provide the new ideas for the fruit storage and preservation.The main research results are as follows:(1)Preparation and characterization of CMC-Na/PVA composite aerogelsCMC-Na/PVA composite aerogels were prepared by freeze-drying method,using CMC-Na and PVA(1:1,v/v)as basic materials.The analysis of Scanning Electron Microscopy(SEM),X-ray Diffraction(XRD),Brunauer-Emmett-Teller(BET)and Fourier Transform Infrared Spectrometer(FTIR)showed that the CMC-Na/PVA composite aerogels are mainly connected by hydrogen bonds,and the blending framework was formed between different molecules without changing the porous structure of the aerogels.The hydrophobic test showed that the composite aerogels had good hydrophobicity.Based on the above characteristic,the water could form spherical water droplets on the surface of the aerogel and maintain its shape within 300 s.The sustained-release experiment showed that the CMC-Na/PVA composite aerogels as the carrier could prolong the release time of essential oils to 15 days,with an average release rate of 5.7%.(2)The control of citrus postharvest green mold by CMC-Na/PVA composite aerogel loaded with essential oilThe in vitro antifungal properties of four combinations of essential oils(citral +cinnamaldehyde,cinnamaldehyde + citronellal,cinnamaldehyde + trans-2-hexenal,citronellal + trans-2-hexenal,citral + citronellal,citral + trans-2-hexenal)were compared.Combining with the cost of practical application,the optimal ratio of essential oil was determined as citronellal + cinnamaldehyde(1:4,v/v),whose minimum inhibitory concentration(MIC)and the minimum fungicidal concentration(MFC)against Penicillium digitorum were 0.40 μL/m L.Citrus fruits were fumigated by CMC-Na/PVA composite aerogels loaded with compound essential oils and stored at room temperature for 30 d.The physiological and biochemical changes of fruits during storage were measured,and it was found that the treatment could effectively inhibit the incidence rate of green mold during storage,and without adverse effect on citrus fruit quality.(3)Control of postharvest gray mold in strawberry by CMC-Na/PVA composite aerogel loaded with essential oilThe antifungal activities of eight kinds of essential oils including trans-2-hexenal,cinnamaldehyde,citronellal,eugenol,carvacrol,myrcene,β-linalool and citral,were compared against Botrytis cinerea were compared,of which trans-2-hexenal had the best antifungal activity,whose MIC and MFC were 0.20 μL/m L.CMC-Na/PVA composite aerogels loaded with trans-2-hexenal fumigated strawberries and stored at room temperature for 6 d.The physiological and biochemical changes of fruits during storage were measured,and it was found that the treatment could effectively inhibit the incidence rate of gray mold during storage and have no adverse effect on strawberry fruit quality.Moreover,treating with trans-2-hexenal effectively induced the activities of antioxidant and resistant enzymes such as peroxidase(POD),catalase(CAT),superoxide dismutase(SOD),and glucan1,3-β-glucasidase(GLU).(4)The control of postharvest anthracnose of pitaya by CMC-Na/PVA composite aerogel loaded with essential oil:The antifungal activities of eleven kinds of essential oils such as trans-2-pentenal,trans-2-hexenal,trans-2-decenal,trans-2-octenal,cuminal and octanal,MIC and MFC of pitaya anthracnose pathogen were compared,which trans-2-octenal had the best antifungal activity whose MIC and MFC were 0.30 μL/m L and 0.60 μL/m L,respectively.CMCNa/PVA composite aerogel loaded trans-2-octenal were fumigated to pitaya and stored at room temperature for 15 d.The physiological and biochemical changes of fruits during storage indicating that the treatment could inhibit the incidence rate of anthracnose and has no adverse effect on the quality of pitaya fruits.In conclusion,the CMC-Na/PVA composite aerogels prepared in this study can be used as the carrier to slowly release essential oils.This method can significantly reduce the decay rate of three southern fruits and without adverse effects on fruit quality,which can provide new ideas for essential oils to control postharvest diseases of fruits.