Multi-method evaluation of volatile flavor compounds in five kiwifruit varieties

【Objective】Fruit wine, as a food of fruit processing, not only enhances the flavor diversity of kiwifruit but also increases its biological activity, leading to the production of kiwifruit wine with a unique flavor, combined fruit with wine aromas, and rich nutrition. The aroma of fruit is a key factor affecting the quality of fruit wine, as it directly impacts the wine's aroma and overall quality. The primary aroma of fruit wine is determined by the fruit variety and origin. However, due to the lack of specialized kiwifruit varieties, the current kiwifruit wines often exhibit such shortcomings as a sour taste, flat aroma, and unbalanced flavor, which restrict the high- quality development of the kiwifruit wine industry. The purpose of this study is to provide a valuable theoretical foundation for the fermentation process of kiwifruit wine and the selection of specialized brewing materials.【Methods】In this study, five kiwifruit varieties (Xuxiang, Hayward, Huayou, Jinyan, and Hongyang) were selected as raw materials. The volatile components of these five kiwifruit varieties were determined using the solid- phase microextraction (SPME) combined with the gas chromatography-mass spectrometry (GC-MS) and chemometrics. The volatile components were compared, and an electronic nose was employed to distinguish the odor substances among the different kiwifruits. The aroma activity value (OAV) was used to assess the contribution of volatile components to the overall aroma, and sensory analysis was performed to describe the olfactory sensations induced by the different kiwifruit aromas. The volatile components of these five kiwifruits were analyzed using SPME-GC-MS, electronic nose technology, and chemometric methods.【Results】In the electronic nose test, the sensor responses of Hayward, Huayou, and Jinyan kiwifruits wereweak, with their radar plots nearly overlapping. In contrast, the W5C, W3C, and W2S sensors of Hongyang and Xuxiang kiwifruits showed strong responses, while the W1W sensor had relatively low response intensity across all varieties. Among the five varieties, Xuxiang kiwifruit exhibited the strongest responses to all sensors, which corresponded to the highest concentration of volatile substances, particularly alcohols and esters. The electronic nose proved to be very effective in distinguishing the odor substances of different kiwifruit varieties. Through SPME-GC-MS analysis, 94 volatile compounds were detected, including 18 alcohols, 44 aldehydes, 4 acids, 18 aldehydes and ketones, and 10 other compounds. The Xuxiang kiwifruit juice contained 29 volatile compounds, Hayward 48 compounds, Huayou 42 compounds, Jinyan 42 compounds, and Hongyang 28 compounds. Among these, alcohols such as 2-methyl-1- butanol, isoamyl alcohol, phenylethanol, hexanol, and eucalyptus oil were the most abundant. Esters included methyl benzoate, ethyl octanoate, ethyl hexanoate, and ethyl isovalerate, while acids such as 2- methylbutyric acid, octanoic acid, and benzoic acid were present in relatively high concentrations. Aldehydes and ketones such as acetaldehyde, benzaldehyde, hexanal, and trans-2- hexenal were also abundant. These compounds are considered key contributors to the characteristic aroma of kiwifruit. Moreover, 75 compounds had an odor activity value (OAV) greater than 1, with Xuxiang kiwifruit juice containing 27 such compounds, Hayward 40, Huayou 32, Jinyan 31, and Hongyang 28. Among the volatile substances with an OAV greater than 1, butyl acetate and ethyl octanoate were present in all five kiwifruit varieties, playing significant roles in enhancing the fresh, fruity, and tropical aromas. Principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA) revealed significant differences in the volatile components across the five kiwifruit varieties. The heatmap further indicated that ethyl butyrate, butyl acetate, trans-2-hexenal, methyl caproate, n-hexanol, and trans-2-hexenol were present in high concentrations across all varieties. Ethyl butyrate was the most abundant volatile compound in Hayward, Xuxiang, and Hongyang kiwifruits, while butyl acetate and n-hexanol were most abundant in Hayward, Xuxiang, and Hongyang kiwifruits. Huayou and Jinyan kiwifruits showed higher concentrations of n-hexanol. Sensory evaluation and electronic nose data suggested that Hayward kiwifruit, which contained the most volatile components, performed best in descriptive terms, being rich in alcohols and esters, with a balanced presence of acids and aldehydes and ketones, resulting in a pleasant aroma.【Conclusion】Butyl acetate and n-hexanol are the key volatile compounds that enhance the complexity and overall flavor characteristics of kiwifruit. Hayward kiwifruit is recommended as the optimal raw material to enrich the aroma profile in kiwifruit wine production.