Taste receptors, chemical kinetics and equilibrium

We recently published an interesting Thesis article by Bruce Gibb called “Life is the variety of spice” and have since received a comment that seeks to extend the ideas originally discussed.

Gavin Armstrong (Associate Editor, Nature Chemistry)

In an insightful article in the January 2010 issue of Nature Chemistry, Bruce Gibb proposed the addition of curry-making to undergraduate organic chemistry labs. Curry-making is a classic example of a practical aspect of chemistry (molecular gastronomy) that laymen tend to ignore. Initially the reagents (spices) are heated (fried) in oil so as to overcome the different activation barriers. After that, water is added to the mixture and boiled, driving the reaction towards equilibrium. There are many rate constants in the first step which is one of the reasons that the ingredients must be heated stepwise at various temperatures. During the final reflux, multiple equilibrium constants are set up. Hence the concentrations of the different spices assume immense importance. A little on the higher side and the curry can become extremely spicy. In fact, the science is delightfully complex and it is astonishing that curry making works more often than not.

While seconding the author’s proposal, we also feel that one should consider adding part of the culinary class to the biochemistry curriculum. The author discusses the essential structural implications of the different curry ingredients and their mutual physico-chemical interactions while it is being prepared. Additionally, one needs to appreciate the biochemical interactions of the curry after consumption and how it’s different ingredients stimulate a diverse array of distinct receptors (often simultaneously) [Gerhold & Bautista, 2009]. Capsaicin, black pepper and garlic all stimulate the TRPV1 receptor [McNamara et al., 2005] whose activation leads to the typical burning sensation. Various oils and cloves stimulate the TRPV3 receptor (highly expressed in the nose) [Xu et al., 2006]. It is the combined downstream effect of these various taste and olfactory receptor stimulations that leads us to appreciate the flavor of curry coupled with the aroma and warmth of cloves.

It is interesting to note that this is not the only way that the TRPV receptors have been put to use in society. In eastern India, plans are underway to equip the police with ‘bhut jolokia’ [Liu & Nair, 2010 and Bosland & Baral, 2007] — the world’s hottest pepper — in an aerosol spray to disperse unruly mobs or immobilize rioters non-violently. Gibb noted that peppers evolved to produce capsaicinoids to ward off herbivores, today these peppers are being used by human intruders as ‘smoke bombs’ to keep wild animals at bay in remote forests.

Culinary science has for a long time been treated as an art by cooks around the world and they are mostly ignorant of the science lurking behind a good recipe. Most programs in gastronomy do little to emphasize its molecular aspects. While good food is certainly aesthetic, it is the chemists who can also appreciate the science behind it. While chemists might not become dedicated cooks, a basic culinary education does have implications in the real world; and trained individuals might cherish the opportunity to apply it in their daily lives and career. Thus there are multiple reasons why we would like to highlight the contribution made by biochemists in understanding culinary science.

Finally, a comprehension of the science behind the curry will certainly make a better cook and good food is a universal healer.

Arnab De [Department of Microbiology and Immunology, Columbia University Medical Center]

Subho Mozumdar [Department of Chemistry, University of Delhi, India]

Rituparna Bose [Department of Geological Sciences, Indiana University, Bloomington; e-mail: ribose@indiana.edu]