## 3 Results and Discussion
### Validation of the Sensory Effect of MECs in Coffee Brews  
To understand the sensory effect of MECs in coffee brews, we studied the amount of 3-MBM that contributed to the top-ranked SCA scores in two coffee brews of different qualities: good quality brews with an SCA score of 77.0 points (control brew) and an excellent quality brew with an SCA score of 84.0 points. Quantitative analyses revealed that the 3-MBM concentrations in good and excellent quality brews were 11.4 and 22.0 nL/L, respectively, confirming that the higher quality brew contained a higher amount of 3-MBM (Figure 2).  
Next, sensory evaluation was performed. Although MECs are known to exist in strawberries and fresh strawberry juice and have fruity fragrance [42; 43; 44], reports on MECs  
Figure 1: MECs strongly correlated with the SCA cupping score studied by non-targeted analysis. (**A**) OPLS model. The SCA cupping score was predicted by chemical information. (**B**) VIP plots. The top 30 variables (compounds) are shown. Arrow heads indicate MECs. (**C**) Correlation plots between the SCA cupping score and the GC–MS normalized area of VIP-01 (**left**), VIP-08 (**center**), and VIP-09 (**right**).  
Figure 2: Quantitative analysis of 3-MBM in coffee brews from two different quality coffee beans. Statistical significance is indicated by the Student \(t\) test (\(\mathbf{\ast}^{\ast}\)\(p<0.01\)).  
in coffee are limited. The odor threshold value of 3-MBM is 5 nL/L, which is calculated using the published threshold of 4.4 \(\mathrm{\SIUnitSymbolMicro g}\)/kg [42] and specific gravity of 0.88 g/mL at 25 \({}^{\circ}\)C. 3-MBM is considered to be odor-active in coffee brews, although the published threshold value was determined in water and the threshold in coffee can be modified in a specific matrix. Spiking the control brews with 3-MBM (10 nL/L) clearly enhanced the fresh, sweet, and fruity aromas (Figure 3A), which are distinguishable from the fruity odor from fermentation caused by ethyl-esterified compounds [45]. Furthermore, the effect of 3-MBM on cleanness of brews was evaluated, because cleanness is one of the most significant indicators of high-quality coffee and a significant factor affecting coffee flavor and impression. Figure 3B shows that the cleanness intensities increased with the addition of 3-MBM (5 or 10 nL/L). Therefore, 3-MBM not only increased the fresh, fruity aroma but also increased the cleanness of the brews (the reduction of off-flavor).  
Recently, [PERSON] et al. reported an enhancing or synergistic effect of perceptual interaction between ethyl-ester aroma compounds in Langjiu [46]. [PERSON] et al. studied the evaluation of the interaction between esters and sulfur compounds in pineapple, suggesting enhancement, masking, and synergistic effects [47]. [PERSON] reported that specific compounds (carboxylic acids (C1, C2, and C4) under odor threshold values) affect other aroma compounds and increase coffee aroma intensities [48; 49; 50; 51]. However, the reduction of off-flavor in coffee brews has not yet been reported. To the best of our knowledge, this is the first study to report that 3-MBM is a compound contributing to the reduction of off-flavor in coffee brews and influencing flavor impression in arabica specialty coffee.