Impact of must clarification treatments on chemical and sensory profiles of kiwifruit wine

This study examined the effect of various clarification treatments on the physicochemical properties, volatile compounds, and sensory attributes of kiwi wines produced from five different kiwifruit (Actinidia deliciosa) varieties. The degree of clarification had a minimal impact on physicochemical parameters, including the content of residual sugar, ethanol, volatile acid, titratable acidity (except for the kiwifruit variety ‘Qinmei’), and the pH value. However, wines made from unclarified juices (muddy juice and pulp) displayed a higher glycerol content than those made from clarified juices. The cluster heat map and principal component analyses (PCA) demonstrated that kiwi wines produced from clarified kiwi juices possessed a higher ester content, whereas muddy juice and pulp wines contained elevated levels of higher alcohols. Quantitative descriptive analysis (QDA) indicated that clarified juice wines outperformed muddy juice and pulp wines in terms of purity, typicality, harmony, intensity, and freshness, with negligible differences in terms of palate acidity. Moreover, the clarified juice wines featured more characteristic kiwi wine aromas (kiwifruit, passionfruit, and pineapple) compared with that of the muddy juice and pulp wines, which exhibited an increased grassy flavour. Although the 100-NTU kiwifruit juice-fermented wine did not show an advantage in the cluster heat map and PCA, it presented better freshness, typicality, and intensity in the QDA, as well as a more passionfruit aroma. Based on the orthogonal partial least-squares discriminant analysis, A. deliciosa ‘Xuxiang’ was deemed to be the most suitable variety for vinification. This study provides crucial insights for enhancing the production of high-quality kiwi wine.

To better identify the differences in the aroma compounds of kiwi wines fermented with different varieties, OPLS-DA was performed with variety as the independent variable and the aroma substance as the dependent variable (Supplementary Fig. 2), including 200 replacement cross-validations to evaluate the model fit.
The ODLS-DA results demonstrated that the intercepts of the R 2 and Q 2 regression lines on the vertical axis were less than 1 and the intersection of the Q 2 regression line with the vertical axis was less than 0, which indicated that the model was not overfitted (Supplementary Fig. 2a) 1,2 , thereby validating the model for the analysis of differences in aroma compounds between different kiwi wines.The different varieties of kiwi wine samples were well differentiated in the score scatter three-dimensional plot of ODLS-DA for aroma compounds (Supplementary Fig. 2b).The 'Xuxiang', 'Yate', and 'Qinmei' wines were clustered separately, whereas 'Huayou' and 'Hayward' wines clustered close together, suggesting similarities in the composition and content of aromatic compounds between these latter two wines.'Qinmei' wine is located in the first quadrant, close to methyl octanoate and phenethyl acetate and diagonally to α-pinoresinol, indicating that 'Qinmei' has the highest content of methyl octanoate and phenethyl acetate and the lowest content of α-pinoresinol (Supplementary Fig. 2c).'Yate' wine had the highest content of 1-pentanol, which could potentially contribute to an unpleasant bitter almond odour that should be avoided as much as possible in kiwi wines 3 .'Huayou' and 'Hayward' are positioned together in the third quadrant close to the fatty acids (octanoic, hexanoic, and decanoic acids) as well as 1-butanol.Fatty acids are important precursors for formation of the ester aroma; thus, the higher fatty acid content in 'Huayou' and 'Hayward' wines implies less accumulation of ester aroma, which is consistent with the aroma distribution trend (Supplementary Fig. 2c).Hexanoic acid gives kiwi wine a soapy odour, which is considered to be a defective aroma 4 .The effect of 1-butanol on the organoleptic aroma of fruit wines has not been studied extensively to date; however, its potential risk to human health should be of concern owing to its methanol-like biochemical properties 5 .'Xuxiang' wine is located in the fourth quadrant closest to the ethyl esters (ethyl lactate, ethyl butanoate, and ethyl acetate), which are considered to be the core aroma components of kiwi wines, contributing to the formation of the typical aroma of kiwi wines 6 .Additionally, higher levels of aromatic compounds were observed in the fourth quadrant, indicating that the sensory performance of the 'Xuxiang' wines may be more prominent.
The variable importance in projection (VIP) parameter was calculated to classify the variances and explain the contribution of variables to the model 7 , where VIP > 1 indicates that the variable contributes significantly to the classification of the samples in each group and can be used as a marker of variance for the component.The VIP analysis showed that the 12 aroma compounds can be used as markers of differences among kiwi wines produced with five kiwifruit varieties (Supplementary Fig. 2d, red columns).

table 3 .
1. Du, H. et al.Discrimination of authenticity of Fritillariae Cirrhosae Bulbus based on terahertz spectroscopy and chemometric analysis.Microchem.J. 168, 106440 (2021).Note: Reducing sugars were measured as glucose and titratable acidity as citric acid.Values are mean ± SD; lowercase letters (a-d) in each column indicate the least significant difference test, and different letters represent significant differences (p < 0.05, Duncan test) between different turbidity of the same kiwifruit variety.The dynamic range indicates the range of maximum and minimum concentration values of the generated standard curve.Volatile components in kiwi wine fermented with different clarified juices of the "Xuxiang" variety (μg/L) Note: Values are mean ± standard deviation.Different lowercase letters in the same row indicate significant differences (p < 0.05, Duncan test)."-"indicates that the reference threshold was not found for this aroma component.Supplementary

table 4 .
Volatile components in kiwi wine fermented with different clarified juices of the "Huayou" variety (μg/L) Note: Values are mean ± standard deviation.Different lowercase letters in the same row indicate significant differences (p < 0.05, Duncan test)."-"indicates that the reference threshold was not found for this aroma component.Supplementary

table 5 .
Volatile components in kiwi wine fermented with different clarified juices of the "Hayward" variety (μg/L) Values are mean ± standard deviation.Different lowercase letters in the same row indicate significant differences (p < 0.05, Duncan test)."-" indicates that the reference threshold was not found for this aroma component.

table 6 .
Volatile components in kiwi wine fermented with different clarified juices of the "Qinmei" variety (μg/L) Note: Values are mean ± standard deviation.Different lowercase letters in the same row indicate significant differences (p < 0.05, Duncan test)."-"indicates that the reference threshold was not found for this aroma component.Supplementary

table 7 .
Volatile components in kiwi wine fermented with different clarified juices of the "Yate" variety (μg/L) Note: Values are mean ± standard deviation.Different lowercase letters in the same row indicate significant differences (p < 0.05, Duncan test)."-" indicates that the reference threshold was not found for this aroma component.