# Harnessing Odorant Receptor Activation to Suppress Real Malodor
## 2 Results and Discussions
### Sensory Deodorization of Cat Urine Odor Using TAAR5 Antagonists  
The significance of this study is that the antagonists of the target odor receptors found in the in vitro evaluation system have been narrowed down to compounds that have been shown to suppress the perception of the odor in perception. We finally conducted a sensory deodorization test on eight fragrance compounds that demonstrated strong inhibitory effects in the cell assays. The eight odors were selected mainly from aldehydes, which had high TAAR5 response inhibition, and compounds with low TAAR5 inhibition, the previously reported antagonist ALC5 (also known as timberol). To prepare the fragrance solutions, we adjusted the concentration of each candidate fragrance compound (0.01% and 0.1%) to ensure that the odor intensity remained subtle. We placed 20 \(\upmu\)L of each fragrance solution on a piece of filter paper inside a 3 L sampling bag filled with odorless air and allowed it to diffuse overnight (Figure 4A). For the cat urine odor, we created a master batch gas by volatilizing 4 g of cat urine in a 10 L sample bag. From this, we extracted 200 mL of gas and injected it into the fragrance air mixture to produce a combined gas sample with both cat urine and fragrance (Figure 4A). As a control, we used 3 L of odorless air mixed only with the cat urine odor. Nine participants evaluated the malodor  
Figure 3: Antagonists of cat urine odorants responsive to TAAR5. **(A)** Outline of the antagonist screening procedure. **(B)** First screening of 400 odorants for the inhibition of TAAR5 responses to cat urine. **(C)** Dose-dependent inhibitory effect of candidate antagonists against TAAR5 in response to cat urine. Antagonist concentration: 0 (white), 1 \(\upmu\)M (light gray), 10 \(\upmu\)M (dark gray), and 100 \(\upmu\)M (black). Error bars indicate standard deviation (s.d. ), n = 3. Multiple comparisons were conducted using one-way analysis of variance (ANOVA) followed by [PERSON]’s multiple comparison test (* \(p<0.05\), **\(p<0.01\), *** \(p<0.001\)). See Table S1 for details of each compound. intensity and pleasantness/unpleasantness of candidate fragrance compounds at 0.01% concentration, while eight participants evaluated them at 0.1% concentration, using a 6-point odor intensity scale and a 9-point hedonic scale, respectively (Figure 4A) [6]. Some fragrances selected based on the TAAR5 response significantly reduced mal-odor intensity and improved pleasantness derived from cat urine odor, outperforming the known TAAR5 antagonist timberol (ALC5), which was used as a reference (Figure 4B,C). Figure 4: TAAR5 antagonists suppressed cat urine malodor. (**A**) Schematic of preparing gas mixture with cat urine and candidate fragrance compounds used in the human sensory evaluation test, candidate fragrance compounds used in this test, and the test condition. (**B**) Results of the evaluation test using 0.01% (\(\
icefrac{{p}}{{v}}\)) fragrance solution showing the malodor intensity (top) and pleasantness (bottom). Each color represents the score of one subject. The median is shown as a black line in each condition. Nonparametric multiple comparisons against mean values were conducted using one-way analysis of variance (ANOVA) followed by [PERSON]’s multiple comparisons test (* \(p<0.05\), ** \(p<0.01\)). (**C**) Results of the evaluation test using 0.1% (\(\
icefrac{{p}}{{v}}\)) fragrance solution showing the malodor intensity (top) and pleasantness (bottom). Each color represents the score of one subject. The median is shown as a black line in each condition. Nonparametric multiple comparisons against mean values were conducted using one-way analysis of variance (ANOVA) followed by [PERSON]’s multiple comparisons test (* \(p<0.05\), ** \(p<0.01\), ** \(p<0.01\)). (**E**). Median is shown as a color arrow in each condition. Remarkably, even at the lower 0.01% concentration, ALD3 (also known as muguet butanal) and ALD6 (also known as bourgeonal) demonstrated significant suppression of both malodor intensity and unpleasantness (Figure 4B).