The Role Of Lipoxygenase In The Formation Of Fresh Waxy Corn Flavor And Its Application In Postharvest Storage

As an important cash crop in China,waxy corn can be used as fresh food if its sugar content reaches 7%.The fresh waxy corn has an extensive market prospect for its relatively high nutritive value,delicate flavor and fat fragrance that are different from other varieties.Its flavor components play an important role in the quality that directly affects the consumers' choice.The fresh waxy corn has relatively complicated flavor components.Its main volatile flavor components are small molecule alcohols and aldehyde produced through lipoxygenase pathway.LOX is the first key enzyme of this pathway,and its role in the flavor formation of fresh waxy corn is not clear.In this paper,waxy corn of "Huziheinuo No.1" in 7 development stages were used as test materials to establish the flavor map of different development stages of fresh waxy corn.The correlation between LOX and LOX isozyme gene in different development stages of waxy corn and the flavor substance in different development stages of waxy corn was analyzed.The effects of LOX precursor,inhibitor and alkaline environment on flavor substances and the expression of LOX isozyme gene were studied in waxy corn.LOX was used as indicator enzyme to determine blanching time,and the relationship between LOX activity and flavor components in postharvest storage of waxy corn was studied,which laid a research foundation for the role of lipoxygenase in the formation of waxy corn flavor in different development and storage stages.The main results are as follows:(1)During the growth of the waxy corn “Huziheinuo NO.1” seeds,the main nutrients were under dynamic changing status,which can be reflected from the reduction of its water contents,the increase of the starch contents,the increase and the decrease of the soluble sugar and protein.Adopted the Odor Activity Value approach,13,8,12,10,10,10,13 volatile flavor components were identified from the seeds of“Huziheinuo NO.1” at its 7 developmental phases respectively.These substances with OAV greater than 1 were the key flavor substances of waxy corn,among which the(E)-2-nonene aldehyde,1-octylene-3-alcohol,2-pentylfuran,octanal,hexanal,2-Heptenal and nonanal were the main flavor components shared by the waxy corn seeds during the whole growth period.The key flavor components made different contributions to the waxy corn flavor at different developmental phases.Through testing the volatile flavor components and applying the Odor Activity Value approach to identifying the key flavor components,this paper initially established the flavor map and the model of flavor evaluation of the waxy corn “Huziheinuo NO.1” seeds at different developmental phases,which provided data support to the change law of the key flavor components in the waxy corn seeds at different developmental phases.(2)There were significant differences in LOX activity,HPL activity and ADH activity among the 7 developmental stages of "Huziheinuo NO.1".Among the four waxy corn varieties,LOX activity was negatively correlated with the accumulation of volatile aldehydes,and positively correlated with the total amount of volatile alcohols.In the development stage of "Huziheinuo NO.1" waxy corn,LOX activity was positively correlated with the total amount of volatile ketonesand the relative expression of Zm LOX1 and Zm LOX2,and negatively correlated with the relative expression of Zm LOX3.Zm LOX1 and Zm LOX2 may play an important role in the formation of the waxy corn flavor.(3)Adding linoleic acid(LA)and linolenic acid(Le A),the substrates for LOX,into the waxy corn seed section may remarkably increase the contents of the volatile aldehyde in the seeds and inhibit the production of the volatile alcohols.Meanwhile,adding the LOX inhibitors nordihydroguaiaretic acid(NDGA)and the propylgallate(n-PG)may significantly inhibit the contents of volatile aldehyde and ketone substances,and increase the contents of the volatile alcohols.The inhibition of the LOX activity under p H 9.0 markedly decreased the key flavor components in the waxy corn,which means LOX was the key enzyme affecting the waxy corn flavor components.The expression of Zm LOX1 and Zm LOX2 increased greatly when elicited by the LOX substrate and decreased when inhibited by the LOX inhibitor,which means that Zm LOX1 and Zm LOX2 may be the main functional genes during the synthesis process of the flavor components in the waxy corn seeds.(4)LOX activity of waxy corn was significantly correlated with fatty acid value,linoleic acid,linolenic acid and hexanal.LOX pathway initiated by LOX was the main cause of oxidative flavor during storage of waxy corn.Blanching can keep the flavor of waxy corn and prolong the storage time.The blanching time of "Huziheinuo No.1" waxy corn before storage should be 15 minutes,at this time,LOX activity was basically passivated,thus reducing the generation of bad flavor during storage.