Shiso (Perilla frutescens var. crispa) Increases Subjective Pleasantness of Steamed Rice With an Enhanced Sulfur-Odor

When olfactory sensitivity is heightened, sulfur-related odors can make steamed rice smell unpleasant. This study investigated whether shiso (Perilla frutescens var. crispa) can enhance the pleasantness of sulfur-odor-enhanced rice. A sulfur-odor-enhanced rice model was created by adding raw onion to steamed white rice. Odor intensity was quantified using odor index equivalents, whereas odor quality was assessed using odor similarity patterns. Subjective pleasantness and emotional responses were evaluated in 41 healthy Japanese women using a Visual Analogue Scale (VAS) and the Positive and Negative Affect Schedule (PANAS). The addition of shiso increased perceived pleasantness compared to the unpleasant odor condition (median VAS score: 6.1 vs. 4.1, p = 0.029). No changes were observed in odor similarity patterns, whereas odor index equivalents showed a slight decreasing trend; however, these results were interpreted descriptively due to the limited number of measurements. Exposure to the sulfur odor-enhanced rice model reduced positive affect and increased negative affect; however, no significant changes were observed in the shiso-containing model. The addition of shiso increased perceived pleasantness of steamed rice with enhanced sulfur-related odors, whereas emotional responses did not change significantly, suggesting that subjective pleasantness and affective responses do not always change in parallel. These findings may inform approaches to improving the pre-consumption sensory experience of staple foods. Because this pilot study included only healthy Japanese women, the findings cannot be generalized to other populations, including pregnant women and patients undergoing cancer treatment.