Nitric Oxide Fumigation On Disease Inhibition And Mycotoxin Removal In Dried Fruit During Storage

Xinjiang is one of the main producing areas of dried fruits in China,being rich in the fruit resources with excellent quality.Among the dried fruits,dried apricot and jujube are the characteristic and representative dried fruits.Nevertheless,they are always prone to mildew(mycotoxins)and insect breeding during the long-term storage,and will lose their edible value,which resulted in the huge economic losses.The main mycotoxins of dried fruits are aflatoxin(AFT)and ochratoxin A(OTA),which are harmful for human health if eaten by mistake.Therefore,it is very important for researchers to develop the dried fruit industry and to study the technical methods of controlling of the fungal diseases and mycotoxins removal.Nitric oxide(NO)is the main gaseous free radical molecule in organisms.It can be used as a highly effective fumigant to affect the activities of related enzymes in organisms,inhibit the germination and growth of fungal spores,and control the fungal diseases of postharvest fruits.In this paper,in order to deal with the problems of fungal diseases and mycotoxins accumulation during storage,jujube and dried apricot from Xinjiang were used as experimental materials.The effect of NO on the storage quality of dried fruits was investigated by gas fumigation technology.Furthermore,the inhibition of NO on fungal diseases of dried fruits and the inhibition mechanism of NO fumigation to dominant fungi were studied.At last,the removal of NO to mycotoxins was determined.The main contents and results are as follows:1.The effects of NO fumigation on inhibition of fungal diseases and storage quality of dried apricot were studied.After fumigated with NO,the effect of NO on the quality of dried apricot was studied using SO2 as the positive control.After fumigation with different concentrations of NO for 3 h,(1)It is found that NO fumigation had a strong inhibitory effect on the diseases caused by A.flavus,A.niger and P.italicum in dried apricot,and NO of 1500 ?L/L could completely inhibit the occurrence of fungal diseases in dried apricot within 72 h after fumigation.(2)Fumigation with NO of 1500 ?L/L significantly(P < 0.05)reduced the occurrence of natural diseases and insect pests of dried apricots.It also could decreased the moldy rate,moth eaten rate,total aerobic microbial count(TAMC)and total yeast/mold count(TYMC)of dried apricot;Fumigation with NO of 900 ?L/L delayed the increase of browning degree,and reduced the decrease of water activity(Aw),water content,titratable acid(TA),total soluble solids(TSS)and reducing sugar,inhibited the oxidation of ascorbic acid(As A)and the loss of nutrients of dried apricot.After fumigation,the residue of NO was in accordance with the current standard.(3)Fumigation of 200 ?L/L NO kept moisture content,Aw and surface color of dried apricot,delayed the weight loss and browning,maintained the TSS,total acid,As A and reduced sugar content of dried apricot at a higher level,and almost no harmful residues remained in the dried apricots.The results showed that NO fumigation inhibited the occurrence of dried apricot diseases to a certain extent and maintained the storage quality.It also improved the food safety.2.The inhibitory effect of NO fumigation on the fungal diseases of jujube and the effect of NO on the storage quality of jujube was studied,using ash jujubes as test materials,the occurrence of A.niger disease was significantly reduced after fumigation with different concentrations of NO for 3 h,NO of 600 ?L/L could completely inhibit A.niger disease,and the inhibition rate could reach 100%,which significantly reduced the fruit quality loss rate,moldy rate,moth eaten rate,browning degree and total number of surface colonies of ash jujube.It also could delay the decrease of moisture,total soluble solids,reducing sugar,titratable acid and As A content of the ash jujube.It showed that NO fumigation significantly inhibited the fungal disease of ash jujube,effectively reducing the loss of nutrients,and well maintained the original quality of ash jujube.3.The inhibitory mechanisms of NO fumigation in vitro on A.flavus,A.niger and P.italicum isolated from dried apricot and jujube were investigated.The inhibitory effect of NO and SO2 on the three fungi was compared.NO fumigation decreased the severity of disease in dried apricots and suppressed colony expansion and mycelial growth in a concentration-dependent manner.The minimum fungicidal concentration(MFC)and minimum inhibitory concentration(MIC)of NO against three fungi were 600,450,450 ?L/L and 33,27,27 m L/L,respectively.MFC and MIC of SO2 against three fungi were 450,450,450 ?L/L and 87,67,27 m L/L,respectively.NO fumigation showed the same or better antifungal effect than that of SO2.Under MFC and MIC conditions,NO fumigation completely inhibited the spore germination and germ tube elongation of dominant fungi in dried fruits,and reduced mycelial biomass.It was found that the inhibition mechanism of NO on fungi was that NO fumigation destroyed the integrity of fungal cell membrane,increased the permeability of fungal cell membrane and oxidative damage,changed the microstructure of mycelium.It led to the inhibition of fungal growth and reproduction.At last,it caused the death of the fungi.4.The effect of NO on mycotoxins production by A.flavus and A.niger was studied,and the action pathway of NO fumigation on mycotoxins removal was clarified.The results in vivo showed that NO fumigation could reduce the decay rate and colony growth of A.flavus and A.niger which caused diseases of dried apricot.It also inhibited the production of Aflatoxin B1(AFB1),Aflatoxin B2(AFB2),Aflatoxin G1(AFG1),Aflatoxin G2(AFG2)produced by A.flavus and inhibited the Ochratoxin A(OTA)produced by A.niger.After 10 d,AFB1,AFB2,AFG1,AFG2 and OTA contents in dried apricot were decreased by 51.53%,49.75%,49.50%,49.13% and 43.88%,respectively.NO fumigation could significantly reduce the accumulation of mycotoxins in dried apricot.The results in vitro showed that NO fumigation had a strong inhibitory effect on the mycotoxin production of A.flavus and A.niger in the medium,and the concentration of NO fumigation was closely related to the content of mycotoxins.The fumigation with low NO concentration(1500 ?L/L,1 time)had only a slight effect on the removal of mycotoxins in the standard solution.However,the fumigation with high NO concentration(150 m L/L,100 times)had a strong effect on the removal of mycotoxins,and the contents of OTA,AFB1,AFB2 and AFG1 decreased by 55.56%,45.51%,1.52% and 35.76%,respectively.It showed that the removal of NO fumigation on mycotoxins was mainly through the following two pathways:(1)NO fumigation controlled the number of fungi in dried apricots and inhibited the growth of fungi in the medium,thus it reduced the production and accumulation of mycotoxins;(2)NO fumigation reduced the content and accumulation of mycotoxins by direct clearance of mycotoxins.In summary,NO fumigation can inhibit the growth of fungi,control the occurrence of fungal diseases,reduce the pollution of mycotoxins to dried fruits.It also ensure the quality of dried apricots and jujubes after storage.It has similar or better effect than treated by SO2.Therefore,NO can be used as an alternative safe and effective gas fumigant for dried fruits during storage.It is a good theoretical and technical foundation for the industrial application for studying the NO fumigation technology.And it is provided the new ideas and directions for the food safety of dried fruit.