# Propolis Hydroalcoholic Extracts: Biochemical Characterization and Antifungal Efficacy
## 3 Results
### Metabolites Potentially Effective Against B. cinerea  
Figure 6 illustrates the analysis conducted using OPLS to correlate the non-volatile metabolites to the EC50 values recorded for the different tested extracts. In the Left Plot (Figure 6), the scatter plot shows the observed versus predicted values of the EC50 for each sample. The R\({}^{2}\) value of 0.9878 indicates an excellent fit, meaning the model predicts the EC50 values with high accuracy. The low RMSECV (Root Mean Squared Error of Cross Validation) of 0.414564 further supports the model's accuracy in predicting EC50 values. Even though the predictive variance explained during leave-one-out cross-validation is close to 1, the limited number of samples does not allow for a generalization of the model due to the strong risk of overfitting; therefore, the results shown should be considered preliminary. The Right Plot of Figure 6 shows the coefficients of different chemical components found in the propolis extracts that influenced the EC50 values. The compounds with negative coefficients are of particular interest, as they appear to lower the EC50, indicating they may enhance the bioactivity of the propolis extracts.  
Chrysin, a natural dietary polyphenol and flavonoid found in flowers, honeycombs and mushroom species that has multiple biological and pharmacological activities [31], has the highest positive coefficient, indicating it significantly decreases bioactivity (higher EC50). Its high coefficient suggests a negative influence on the potency of the extract, although previous research highlights chrysin's antioxidant and anti-inflammatory properties [31]. Naringenin also has a large positive coefficient, although slightly lower than that for chrysin, implying it contributes substantially to reducing bioactivity of the propolis extract. Known for its antioxidant and anti-cancer properties [32] and antifungal activity [33], naringenin appears to contrast the extract's potency.  
With a significant negative coefficient, luteolin is compound that boosts bioactivity by reducing the EC50. This supports its known biological effects, including antifungal activity supressing mycelial growth and pathogenicity of _B. cinerea_ and _P. expansum_[34]. Apigenin  
Figure 5: Effect of volatile and non-volatile metabolites produced by PFvg1, PFvg2, PU3, PV4 and PT5 propolis extracts obtained using 90% ethanol solution and 1 day of extraction, preceded by 20 min of sonication, on _Botrytis cinerea_ disease incidence (%) on table grapes (**a**) and blueberries (**b**). Different letters indicate significant differences within the propolis according to [PERSON]’s test (\(\alpha=0.05\)).  
also shows a substantial negative coefficient, suggesting an improved bioactivity of the extract, confirming its antifungal activity [35]. Chrysoeriol, while contributing less than the above, still shows a negative coefficient, indicating a role in enhancing bioactivity. [PERSON] et al. [36] reported chrysoeriol's antifungal activity as well. Several compounds, including vanillin, rhamtein, quercetin, protocatechuic acid and p-coumaric acid, have near-zero or positive coefficients with relatively low magnitude. This suggests that these compounds either do not significantly influence the EC50 value or may slightly reduce the potency of the extract.