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

Kiwifruit wine, a novel fruit wine with high nutritional value, has the potential to expand the kiwifruit value chain. However, its market growth is hindered by a flat taste and lack of aroma. Existing research focuses on yeast strains, fermentation temperature, and fruit variety, but less attention is paid to brewing technology, specifically juice clarification. Clarification removes solid particles from the juice, which can significantly impact aroma composition and organoleptic properties. Previous studies on grape and apple wines have shown conflicting results regarding the impact of clarification on aroma and sensory attributes. Some research suggests that clarification removes aroma compounds or essential nutrients for yeast, negatively affecting aroma. Others found a non-linear relationship, with factors such as fermentation system, clarifying agent, and yeast type influencing the outcome. This study aims to investigate the effect of different clarification levels on the quality of kiwi wine by analyzing physicochemical parameters, volatile compounds, and sensory qualities of five kiwifruit varieties. The findings will provide insights into optimizing kiwi wine production.

The sensory quality of kiwi wine is crucial for consumer preference. Existing research on kiwi wine mainly focuses on yeast strains, fermentation temperature, and kiwifruit variety. Non-*Saccharomyces cerevisiae* fermentation has shown potential for aroma improvement, but often faces challenges in large-scale applications. The role of juice clarification in fruit wine production is well-established for white wine but remains relatively unexplored for kiwi wine. Studies on grape and apple wines show conflicting results regarding the effects of clarification on aroma profiles, suggesting that the relationship might be complex and influenced by multiple factors like the type of clarifying agent, fermentation parameters, and yeast strain. There is a need to understand the specific influence of clarification on kiwi wine.

Five *Actinidia deliciosa* varieties ('Xu Xiang', 'Huayou', 'Hayward', 'Qinmei', and 'Yate') were used. Kiwifruit juice was clarified to achieve different turbidity levels (100 NTU, 200 NTU, 300 NTU) using bentonite, with muddy juice and pulp samples also included. *Saccharomyces cerevisiae* CEC01 was used for fermentation at 20°C. Physicochemical parameters (reducing sugar, alcohol content, pH, titratable acidity, volatile acids, glycerol, ammonium, CIELab color) were measured. Volatile compounds were analyzed using headspace solid-phase micro-extraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS). Sensory evaluation was conducted by a trained panel (11 tasters) using quantitative descriptive analysis (QDA) to assess purity, typicality, harmony, intensity, acidity, and freshness, along with aroma descriptors (kiwifruit, passionfruit, grapefruit, pineapple, grassy). Statistical analysis involved one-way ANOVA with Duncan's test, PCA, and orthogonal partial least-squares discriminant analysis (OPLS-DA).

Clarification minimally affected most physicochemical parameters. Unclarified wines (muddy juice and pulp) had significantly higher glycerol content than clarified wines. Cluster heatmaps and PCA showed that clarified juice wines had significantly higher ester content, while unclarified wines had higher levels of higher alcohols (isobutanol and isoamyl alcohol). QDA revealed that clarified juice wines scored higher in purity, typicality, harmony, intensity, and freshness compared to unclarified wines, with similar acidity scores. Clarified juice wines also exhibited stronger kiwifruit, passionfruit, and pineapple aromas. Unclarified wines showed increased grassy notes. Although the 100-NTU wine didn't show an advantage in cluster analysis and PCA, it demonstrated better sensory attributes in QDA. OPLS-DA indicated that 'Xuxiang' was the most suitable variety for vinification. Table 1 presents the physicochemical properties of all kiwi wines, including reducing sugar, alcohol content, titratable acidity, volatile acids, pH, glycerol, ammonium, and CIELab values for each variety and clarification level. Figure 1 shows the cluster heat map of volatile compounds, highlighting differences between clarified and unclarified wines. Figure 2 displays the PCA of aroma compounds, demonstrating the separation of wines based on clarification and variety. Figure 3 presents the QDA results, showing sensory attribute scores for each treatment group. Supplementary Tables provide detailed data on volatile compounds.

The findings demonstrate that juice clarification significantly impacts the aroma profile and sensory quality of kiwi wine. The higher ester content in clarified wines contributes to the improved sensory attributes and characteristic kiwi aromas. The elevated levels of higher alcohols in unclarified wines lead to undesirable grassy notes and negatively affect overall sensory scores. The minimal impact of clarification on most physicochemical parameters suggests that the observed sensory differences are primarily due to changes in volatile compound profiles. The contradictory findings in previous literature regarding clarification’s impact on aroma could be explained by the complex interplay of factors such as clarifying agent, yeast strain, and fermentation conditions. This study emphasizes the importance of sensory evaluation alongside chemical analysis in optimizing kiwi wine production. The identification of 'Xuxiang' as the most suitable variety provides valuable information for cultivar selection.

This study provides crucial insights into the impact of must clarification on the quality of kiwi wine. Clarification enhances the sensory attributes and characteristic aromas of kiwi wine by increasing ester content and reducing higher alcohols. 'Xuxiang' is identified as an optimal variety for vinification. Future research should focus on exploring different clarifying agents and optimizing clarification parameters for specific kiwifruit varieties to further enhance kiwi wine quality.

The study used only one yeast strain. The sensory panel was relatively small and might not fully represent the broad consumer preferences. Further research with larger panels and various yeast strains is recommended to strengthen the generalizability of the findings. Additional research could explore the impact of other processing factors on kiwi wine quality.