## 4 Discussion
The analysis of ester content in apples after treating them with individual and combined EOs for _B. cinerea_ control has provided valuable insights into enhancing apple aroma and flavor. These findings align with existing literature [27; 28], emphasizing the influence of essential oils on fruit ester compositions. Notably, ethyl propionate, evoking a pear-like aroma, peaked with the Fun+Cin+Eug combination, underscoring EO treatments' capacity to elevate specific esters [29]. Ethyl acetate, known for its sweet, fruity scent, was most abundant when using the Fun+Cin+Eug combination (Table 2), supporting the concept that EO applications enhance apple fragrance [30]. Similarly, ethyl isobutyrate concentrations were highest in the Fun+Cin+Eug combination, reinforcing the idea of essential oils modifying ester profiles [31]. The predominance of ethyl 3-methylbutanoate in the Fun+Eug group, offering fruity and pineapple-like notes, supports EO treatments' role in increasing ester production [32]. The prevalence of propyl acetate, which imparts fruity, pear-like notes, in the Fun+Thy+Cin+Eug combination aligns with earlier research on EO treatments [26]. In general, our results indicate that the observed variations in esters likely arose from the complex biochemical interactions between essential oils and plant cellular metabolism, potentially activating stress-responsive pathways that trigger enhanced secondary metabolite production and enzymatic transformations. Ethyl butyrate, reminiscent of pineapple, reached its zenith with the Fun+Thy+Cin+Eug combination, highlighting EO combinations' ability to intensify apple's fruity fragrance [32]. Butyl acetate, contributing a banana-like aroma, had its highest concentration in the Fun+Thy+Cin+Eug combination (Table 2), in line with prior research on EO effects [33]. The notable rise in ethyl pentanoate with the Fun+Thy+Cin+Eug combination underscores the potential of combined essential oils to enhance apple fragrance. Hexyl acetate was most abundant in the Fun+Cin+Eug combination, consistent with the understanding that EO treatments influence specific esters [33]. Ethyl hexanoate, contributing a sweet and fruity aroma, was most prominent with the Fun+Cin+Eug combination, aligning with the literature's suggestions on EO impacts on ester profiles [34]. Notably, the significant concentration of ethyl heptanoate with the Fun+Thy+Cin+Eug combination reflects the substantial impact of EO treatments on enhancing its production. Moreover, the highest concentration of (Z)-3-hexenyl acetate in the Fun+Cin+Eug combination aligns with previous research affirming EO effects on ester content [17]. Finally, the peak concentration of ethyl ocanoate in the Fun+Thy+Cin+Eug combination highlights EO treatments' ability to affect ester levels, contributing to a richer and more complex apple aroma, consistent with the findings of [33]. In the study on the protective effect of essential oils, it was reported that the Thy+Eug+Fun group had the highest ester content among the treatment groups [12]. On the contrary, in our findings, it was determined that the Fun+Thy+Cin+Eug group had the highest ester content. In addition, while the highest ester concentration was determined in the Thy+Cin+Fun treatment (856.9 \(\upmu\)g L\({}^{-1}\)) [12], the highest ester concentration was determined in the Fun+Thy+Cin+Eug (715 \(\upmu\)g L\({}^{-1}\)) treatment in this study. Intriguingly, ethyl 3-hydroxybutyrate showed consistent concentrations across multiple treatments, warranting further investigation into its behavior in response to EO treatments, as it exhibits a unique characteristic. These results collectively demonstrate the potential of EO treatments, individually and in combination, to modulate ester compositions in apples, enhancing their aroma and flavor profiles. The concentration of various C6 compounds and alcohols in apples following treatments against _B. cinerea_ is a critical aspect of understanding the impact of these treatments on apple quality and aroma.