Effect of nitric oxide on volatile compounds in 'Feicheng' peach fruit during cold storage

【Objective】Aroma volatile is an important sensory quality attribute of fruit contributing to con-sumer acceptance. To disclose the possible role of exogenous nitric oxide(NO) in changes of volatiles ofpeach fruit during cold storage(5 ℃),the effects of NO on the biosynthesis of some volatile compoundswere investigated in‘Feicheng'peach fruit.【Methods】‘Feicheng'peach fruit(Prunus persica L. Batsch,‘Feicheng') at physiological mature stage were fumigated with NO gas for 3 hours. Three treatments ofNO(0,5 and 10 μL·L^-1) were assessed. Volatile aroma compounds,including alcohols,aldehydes andesters were determined in peach fruit using GC-MS. The volatile compounds were indentified using Na-tional Institute for Standards and Technology(NIST) mass spectra library. The quantitative determinationof individual compounds was obtained using the peak of internal standard(2-octanol) as relative value.The activities of aroma-related enzymes were also investigated according to a reported method. One unit(U) of alcohol dehydrogenase(ADH) activity was defined as the amount of enzyme required to produce 1μmol of NADH in 1 min. One unit(U) of alcohol acyltransferase(AAT) activity was defined as the in-crease of absorbance at 412 nm per minute. One unit(U) of lipoxygenase(LOX) activity was defined asthe activity that produced an optical density of 1,at 234 nm in 1 min. Specific enzyme activities were ex-pressed U·mg-1protein.【Results】The volatile compounds in peach fruit were measured by headspace SPME,and the volatile profile of‘Feicheng'peach was dominated by alcohols,aldehydes and esters.For alcohols,the contents of 1-pentanol,E-2-hexen^-1-ol,hexanol and 1-hexen-3-ol in peach fruit in-creased before day 2 and then declined in all treatments,while that of nonanol decreased gradually dur-ing storage. Total content of alcohols decreased with the extending of storage time,and the decrease in to-tal alcohols was delayed by treatments with 5 and 10 μL·L^-1NO. The delay caused by the treatment with10 μL·L^-1NO was greater than that by the treatment with 5 μL·L^-1NO. The main aldehyde compounds in-cluded Z-3-hexenal,hexanal,decanal,E-2-hexenal,benzaldehyde and nonanal. Contents of Z-3-hexenal,hexanal,decanal,E-2-hexenal,benzaldehyde and nonanal in the control and in the treat-ments with 5 and 10 μL·L^-1NO increased before day 10 and were significantly higher than those at day40. E-2-octenal and E-2-decenal in the control and the treatments with NO were not detected before day10,and Z-2-heptenal could only be detected in NO treatments. Total content of aldehydes in the controlfruit declined with storage time. However,in the treatments with NO,it increased slightly after 2 days ofstorage and then decreased. The decrease in content of total aldehydes was delayed significantly by thetreatment with 10 μL·L-1NO. The main ester compounds included ethyl acetate,hexyl acetate,E-2-hexenyl acetate,Z-3-hexenyl acetate and ethyl octanoate. Total content of esters in the control fruit in-creased during storage. In treatments with NO,the content of ethyl acetate at day 40 was higher than thatbefore day 10,but lower than that of the control at day 40. It was worth noting that the content of hexyl ac-etate in the control and all treatments decreased sharply from day 10 to 40. For all treatments and the con-trol,contents of E-2-hexenyl acetate,Z-3-hexenyl acetate and ethyl octanoate increased in 10 daysand decreased sharply at day 40. Fruit treated with 10 μL·L^-1NO had higher contents of E-2-hexenyl ac-etate,Z-3-hexenyl acetate and ethyl octanoate at day 40 than the control and the treatment with 5 μL·L^-1NO. Total content of esters in the control peach fruit peaked at day 20 and then decreased with storagetime to the lowest level at day 40. In general,the contents of total alcohols and total aldehydes decreasedduring cold storage,but the total content of esters increased. Compared with the control,the decrease inthe contents of total alcohols and total aldehydes,and the increase in content of total esters were delayedby NO treatment. The delay caused by the treatment with 10 μL·L^-1NO was greater than that by the treat-ment with 5 μL·L-1NO. The ADH activity in peach fruit increased to the peak at day 5 and then de-creased with storage time. Treatments with NO inhibited ADH activity. However,there was no significantdifference in ADH activity between dosages of NO,although ADH activity in peach fruit treated with 5μL·L^-1NO was higher than that in fruit treated with 10 μL·L^-1NO. The AAT activity in the control hadan increasing tendency within the first 10 days,and then rapidly decreased to a relatively low level. AATactivity the treatment with 5 μL·L^-1NO decreased and was lower than that of the control after day 5. Com-pared with the control and treatment with 5 μL·L^-1NO,treatment with 10 μL·L^-1NO had a significantlylower AAT activity within the first 30 days. The difference in AAT between treatments with 5 and 10 μL·L^-1NO was not significant after day 30. LOX activity increased during storage. Fumigation with NO inhibitedLOX activity after day 10 of storage. The LOX activity in treatment with 10 μL·L-1NO was lower thanthose in the control and treatment with 5 μL·L^-1NO.【Conclusions】NO plays important roles in regulat-ing volatile biosynthesis in peach fruit. It delays the changes in the contents of volatile compounds,inhib-its the activities of aroma-related enzymes,and maintains qualities of peach fruit during cold storage.The results suggest that there is pathways of volatile production in peach fruit that are NO-regulated inaddition to that by ethylene. However,further work should be done to study the roles of NO,such as thesignaling pathway,in regulating volatile productions in fruit,which is helpful for improving the sensoryquality and increasing consumer acceptance of peach fruit.