## 4 Discussion
Comparing these findings with the existing literature can provide insights into the significance of the observed variations in these compounds. The highest hexanal concentrations observed in the Fun+Cin and Fun+Cin+Eug groups are consistent with previous research indicating that essential oil treatments can influence the release of volatile compounds like hexanal, contributing to enhanced aroma profiles in fruits [35; 36]. Hexanal, a key contributor to apple aroma, exhibited notable differences among the treatment groups. The minimal variation in (E)-2-hexanal across treatments suggests its stability in the face of essential oil applications, possibly indicating the specificity of essential oils' effects on different C6 compounds. The peaking of (Z)-3-hexanal concentrations in the Fun+Thy+Eug group aligns with the notion that essential oils, particularly cinnamon and fennel oils, have the potential to affect the production of this compound, which is known for its green, leafy notes [37]. The peaking of hexanol concentrations in the Fun+Cin+Eug group is in line with research that demonstrates the capacity of specific essential oil combinations to influence the presence of this alcohol, contributing to the overall aroma complexity of apples [23]. Moreover, the low hexanol concentrations in the control group emphasize the potential of essential oil treatments in maintaining or increasing the levels of these alcohols. 1-octen-3-ol, with its highest concentration in the Fun+Thy+Eug group, suggests that this specific combination of essential oils exerts a more pronounced influence on its levels. 2-heptanol's relatively stable concentrations across treatments support the idea that essential oil applications have a limited impact on this alcohol, consistent with previous findings [38]. Previous research indicates the potential of thymme, cinnamon, and fennel essential oils to modify the concentration of 1-octen-3-ol, thus contributing to apple aroma complexity [39]. The significant variation in 2-ethyl hexanol concentrations across groups, with the highest in the Fun+Thy+Eug group and the lowest in the Fun+Eug group, suggests that these specific essential oil combinations can distinctly impact the production of this alcohol, further enriching the aroma complexity of apples [40]. Heptanol's range of concentrations across treatments, with a peak in the Fun+Thy+Cin group, aligns with the literature highlighting the influence of essential oil combinations on alcohol contents in fruits [41]. In contrast to the study in which it was reported that the protective effect of essential oils had no effect on alcohol content in post-harvest apples [12], it was found in this study that the curative result significantly affected the alcohol content. The reason for this increase can be assumed that the pathogen causes the rise in these components in the curative effect. The varied concentrations of nonanol, octanol, phenylethyl alcohol, and benzyl alcohol across treatments underscore the unique effects of different essential oil combinations on these compounds, which play essential roles in shaping apple aroma profiles [42]. The heatmap, which employs color to represent compound concentrations, serves as a valuable tool for visualizing and interpreting the data. In the context of this paper, darker colors, namely deep blue or purple, denote higher compound levels, while lighter colors, such as green or yellow, indicate lower levels. This visualization effectively conveys the varying degrees of presence of different VOCs across the diverse treatment conditions applied to combat _B. cinerea_ in the harvested apple fruits. The application of heatmaps in metabolomics and chemical analysis is well-documented in the literature [23]. These visualizations are instrumental in highlighting the differences in compound abundance among various experimental conditions. Similar to our findings, previous works have used heatmaps to illustrate how specific treatments or interventions may lead to distinct chemical profiles [23; 43].