Skin Greasiness And Aroma Volatiles Of Apples As Influenced By N-Butanol During Storage

Apple（Malus domestica Borkh.）fruit develop skin greasiness during postharvest storage,reducing fruit quality.It was found that the accumulation of fluid wax constituents responsible for skin greasiness,comprise mainly oleate and linoleate esters of（E,E）-farnesol and short-chain alcohols（C3-C5）.Providing apple fruit with a substrate related to volatile ester synthesis can increase the volatile esters content.As the synthesis of volatile esters depends on the preference of related esters synthase and substrate availability,the development of skin greasiness is believed to be related to the volatile alcohols,the substrates of greasy esters.In order to investigate the effects of volatile alcohols on skin greasiness and aroma volatile during storage,further prove the mechanism of skin greasiness and investigate new ideas of volatile research,the effects of different concentrations of n-butanol（NBA）treatment on cuticular wax,skin greasiness and volatile esters were analyzed in the slightly greased-apple‘Gala’and the severely greased-apple‘Cripps Pink’.At the same time,the changes of soluble solids,titratable acid,respiration rate,ethylene production and fruit firmness were analyzed.The results show that:1.During storage at ambient temperature,‘Gala’fruit developed slightly greasy,while‘Cripps Pink’fruit developed severely greasy.NBA treatment significantly promoted the accumulation of fluid wax constituents in the cuticular wax of‘Gala’and‘Cripps Pink’,and promoted skin greasiness of‘Gala’and‘Cripps Pink’,especially 25μL·L^-1NBA treatment.Therefore,NBA treatment promotes the development of skin greasiness by increasing the accumulation of fluid wax constituents in apples.2.The expressions of MdKASIII,MdSAD6,MdWSD1 and MdLTPG1,involved in wax synthesis and transport,were increased during storage and were up-regulated by n-butanol treatment,suggesting that these genes may be involved in the development of apple skin greasiness.3.There was no significant change in soluble solids and titratable acids in fruits treated with n-butanol.25μL·L^-1NBA treatment delayed the peak of respiration and ethylene production in‘Gala’fruit,and the ethylene production peak of 100μL·L^-1NBA treated fruit increased significantly.However,NBA did not significantly affect the respiration rate and ethylene production of‘Cripps Pink’fruit.This suggests that the effects of NBA on greasiness are via a direct influence on the greasy ester synthesis pathway,rather than via some indirect influence on fruit ripening or senescence.4.The application of exogenous NBA promoted the release of volatile esters in apples during storage.At the initial stage of storage（3 d）,the content of volatile esters in the treated fruit was about 3 times as much as that in controls,among them the content of butyl esters was about 10 times as much as that in controls.The content of butyl esters in NBA treated‘Cripps Pink’fruit was about 3 times of that in the control fruit on day 7.Exogenous NBA treatment increase the synthesis of greasy esters and volatile esters.In the initial stage of storage,low greasy esters and aroma content are restricted by the unavailability of substrates.Meanwhile,it is further proved that skin greasiness of apples is mainly caused by the accumulation of oleate and linoleate esters of（E,E）-farnesol and short-chain alcohols（C3-C5）.