The Influence Of Glycosidically Bound Volatile Components In Kiwifruit Juice And Its Key Processing Steps On Aroma

Kiwifruit,with its rich nutritional value,is favored by consumers.The volatile substances are the basic characteristic flavor of kiwifruit juice.Various types of volatile substance constitute the unique flavor of kiwifruit juice and are also the key index of its kiwifruit juice quality evaluation.The purpose of this study is to investigate the aroma characteristics of the glycosidically bound volatile in kiwifruit juices of different varieties and different ripeness stages and to study the influence of key technological steps on the content of the glycosidically bound volatile and free volatile in the process of juice production.The results are as follows:(1)The glycosidically bound volatiles of kiwifruit juice aroma substances were separated and extracted by Amberlite XAD-2 resin,and their content determined by the ultraviolet spectrophotometer method.Firstly a single factor experiment was employed to analyze the impact of column flow rate,eluent proportion(pentane: methylene dichloride),and liquid recycle ratio(methanol: ethyl acetate)on separation of the glycosidically bound volatile.On this basis,three factors and three levels of response surface tests were designed to optimize the extraction conditions.The results showed that the optimal extraction parameters were as follows: the column flow rate was 2 m L/min,pentane: dichloromethane(v/v)ratio= 3:1,and methanol: ethyl acetate(v/v)ratio= 1:6.(2)Headspace solid-phase microextraction combined with mass spectrometry was used to determine the glycosidically bound volatile in six kiwifruit juices.A total of 45 glycosidically bound compounds were detected.Under the condition of OAV>0.1,the PCA analysis of 11 compounds in the glycosidically bound volatiles indicated that those in Hayward,Cuixiang,and Qinmei juices were similar to each other in the characteristic aroma substances,which were mainly 3-methyl-1-butanol and 3-hydroxy-2-butanone.The glycosidically bound volatiles of Huayou and Yate juices are similar in the characteristic aroma,mainly including octanal,decaldehyde,6-methyl-5-heptene-2-one,and geranyl acetone.However,the characteristic aroma of the glycosidically bounded volatile of Xuxiang juice is significantly different from those of other fruit juices.Xuxiang fruit juice is closely related to nonanal,(Z)-2-hexene-1-ol,and D-limonene.The characteristic aroma of glycosidically bound aroma is mainly green,fruit,hay and fatty.(3)Headspace solid-phase microextraction combined with GC-MS was used to investigate the changes of glycosidically bound volatile in kiwifruit juices at different ripeness stages,i.e.unripe,ripe,and overripe.A total of 49 glycosidically bound volatile compounds were detected in kiwifruit juices at different ripeness stages from three varieties.The total amount of glycosidically bound volatile in Hua You and Xuxiang juices increased from unripe stage to ripe stage and decreased from ripe stage to overripe stage.However,the same trend was not found in Qinmei juice at different ripeness stages.PCA analysis of kiwifruit juice at different stages of ripeness with OAV>0.1 showed that the characteristic aromas of unripe kiwifruit juice were decanal,styrene and geranylacetone,while at the overripe stage they were 1-hexanol,1-octanol and 3-methyl-1-butanol.The aromatic characteristics of the Huayou juice at maturity are similar to those of the Huayou juice at overripeness,with ?-pinoresinol and(Z)-2-hexenol.In addition,the main glycosidically bound volatile of Xuxiang juice at the over-ripe stage were characterized by ?-pinoresinol and(Z)-2-hexenol.(4)Headspace solid-phase microextraction combined with gas-phase mass spectrometry was used to analyze the free volatile and glycosidically bounded volatile of Xuxiang fruit juice treated with different key process steps(extraction,sterilization,and homogenization).The results demonstrated that enzymatic hydrolysis could increase the content of free volatile substances such as aldehydes,ketones,and terpenes in fruit juice and could enhance the free volatile characteristics.In addition,ultrasonic wave and high-temperature pasteurization could positively regulate the fruit juice aroma quality,while ultraviolet pasteurization could not maintain the fruit juice aroma quality.Compared with pressure homogenization,shear homogenization is more beneficial to fruit juice flavor.