Cross-modal spicy enhancement with odour and electrical tongue stimulation

Spicy substances like chili pepper and wasabi can have both beneficial and adverse effects on human health. In particular, they may help to reduce salt intake and limit fat absorption, when consumed in appropriate amounts. However, excessive consumption of spicy foods could increase the desire for more intense spiciness, potentially leading to overconsumption. To address the challenge of balancing the amount of spicy substances in food and the desired level of perceived spiciness, electrical tongue stimulation (ETS) has been proposed as a method of sensory enhancement. Although promising, the effectiveness of ETS remains limited due to safety constraints, highlighting the need for alternative or complementary solutions, such as combining ETS with olfactory stimuli. While congruent odours are well-known to enhance taste perception, their role in modulating spiciness remains underexplored. The present study aims to investigate the cross-modal relationship between olfactory cues and spicy perception using anodal ETS. We have defined two key dimensions of spicy perception based on receptor activation: Piquancy (the burning/stinging quality mediated by TRPV1/TRPA1) and Freshness (the cooling and refresh quality mediated by TRPM8). To examine our hypotheses, we conducted a psychophysical experiment where 35 participants received combinations of anodal ETS at five current levels (0, 0.5, 1.0, 1.5, and 2.0mA) and one of four odours (wasabi, clove, lemon, and vanilla), which they had to rate based on their perceived intensity on visual analogue scales. Our results showed that congruent piquant odours (i.e., wasabi and clove) combined with anodal ETS significantly enhanced the piquancy perception, but did not affect freshness. Conversely, congruent fresh odours (i.e., lemon and vanilla) enhanced the freshness perception without affecting the piquancy perception, and did not interact with ETS. These findings provide new insights into how spiciness can be modulated using minimal pungent substances, potentially increasing both the perceived intensity and overall satisfaction of spicy foods.