The Science of Spiciness

The Science of Spiciness

by Hoi Kiu Wong

Image taken from Qi House of Sichuan/Facebook 

INTRODUCTION 

Spicy food. You are either enjoying the pain as the chilli burns your mouth, or gobbling down a trillion litres of milk in your attempt to remove the excruciating heat sensation off your tongue. In this article, we will explore the science behind spiciness, how spiciness is measured e.g. using the Scoville Heat Index, and the best ways to relieve the spiciness. 

SCIENCE OF SPICINESS

Spiciness, unlike ‘sweet’, ‘salty’ or ‘sour’, is not actually a taste - but it is actually more of a ‘sensation’. When you eat spicy food, certain compounds are released from it that can cause receptors on your tongue to become activated (or excited) and these receptors are called polymodal nociceptors; the same receptors in the body that respond to heat [1]. Hence, eating spicy food can trigger a similar neural pathway to the Central nervous system (CNS) as that of touching a hot object - but the responses are still distinct to one another due to the difference in stimuli. Essentially, the spiciness triggers a ‘fight-or-flight’ response - causing the person to look for ways to cool down or remove the spicy sensation, and you may start to sweat - which is involved in the body’s homeostatic thermoregulatory response [1]. An example of a compound from spicy food that activates the polymodal nociceptors is capsaicin - the main ingredient in chile peppers (See Fig. 1). In this case, it specifically binds to the TRPV1 receptors - therefore signals are transmitted through the trigeminal nerve, causing the brain to detect the hot sensation on your mouth (See Fig. 2). Simultaneously, It can also stimulate the nerves that detect mild increases in temperature - thus, capsaicin sends two messages to the brain - one of which is ‘intense heat’ and ‘warmth’ - creating a long burning sensation. Menthol, a compound found in peppermints, does the opposite effect of spicy food. It can cause a cooling sensation as it activates the receptors that register cold temperatures [2].

Fig. 1 Chemical Structure of Capsaicin 

Photo Credit: Essential Oil 

Fig. 2 TRPV1 Receptor 

Image taken from https://www.cayennediane.com/can-you-be-desensitized-to-spicy-food/

If spiciness is a sensation, why are there different forms of ‘spiciness’? Well, that is due to the difference in the types of compounds found in these various spicy foods. Capsaicin, and piperine found in black pepper and chili peppers are made of larger molecules called alkylamides - and the spiciness stays in your mouth; on the other hand, mustard, horseradish and wasabi are made of smaller molecules called isothiocyanates, that can easily move up into your sinuses and therefore causing that spicy ‘tingling’ feeling in your nose, alongside the burn in your mouth [1]. A specific example of a pepper that contains alkylamides is the Sichuan pepper, commonly used as an ingredient in chinese cuisine dishes. It produces a distinct numbing sensation and if combined with chili pepper creates the Mala flavour. It was found that the pepper included polyphenols as well and the types of alkylamides present are sanshools and hydroxyl sanshools (from the same family as piperine and capsaicin) - which creates the buzzing mouth sensation after consuming. This ‘buzzing’ sensation is what makes Sichuan pepper unique as it is caused by modulating two-pore potassium channels instead of activating TRPA1 or TRPV1 channels [3]. 

Paul Rozin, a psychologist from the University of Pennsylvania, developed a theory of ‘benign masochism’ which helps explain why some people love eating spicy food. According to Rozin, people who enjoy the burning sensation are those that are attracted and enjoy doing other ‘intense sensations’. This discomfort turns into a pleasurable experience after the person is exposed to a sensation a certain number of times [4]. Furthermore, it was found that people can train and gain tolerance against spicy food not because the spice has reduced but because you get tougher. A study has shown that the pain from spicy food is the same for all - two groups, one that can’t tolerate spiciness, and the other that can tolerate spiciness, rated the ‘spiciness’ level the same. This ‘tolerance’ is merely to do with the enjoyment one gets from the burning sensation [1]. 

THE SCOVILLE HEAT INDEX 

The Scoville heat index was invented in 1912 by pharmacologist Wilbur Scoville - a method of measuring ‘spiciness’ [4]. The ‘spiciness’ is measured in Scoville heat units (SHU), which are the number of times a chili extract must be diluted in water for it to lose its heat. Bell peppers rank the lowest at 0 SHU, jalapeños score 3000 to 6000 SHU, and habaneros generate 300,000 SHU. Capsaicin (hydrophobic, colourless, odorless and crystalline-to-waxy solid at rtp) measures 16,000,000 SHU [5]. See Fig. 3 for the Scoville heat index and SHU for different foods. 

Fig. 4 The Scoville Heat Index 

Image taken from https://www.alimentarium.org/en/magazine/infographics/scoville-scale [4] 

©Alimentarium 

BEST WAYS TO RELIEVE THE SPICINESS

It is well known that drinking milk, or acidic food or drink, and carbohydrates e.g. bread, can effectively cool down your mouth after eating spicy food - how do they do this? 

Milk contains a lipophilic protein called casein (lipophilic meaning ‘fat-loving’) which means that it can move towards the capsaicin (as the capsaicin contains a long hydrocarbon tail) and will help ‘flush out’ the capsaicin - like washing the grease off your frying pan with detergent. Note that it must be mammal’s milk as plant-based milks e.g. soy, rice, coconut or almond don’t contain casein [6]. Acidic food or drink can also reduce the burning sensation because capsaicin is alkaline; thus neutralisation occurs. Eating carbohydrates also help cause it can absorb capsaicin molecules or act as a physical barrier between the capsaicin and the TRPV1 receptors on your tongue [7]. Drinking water is not a good idea because it is polar whereas capsaicin is non-polar, so the water will just spread the capsaicin around your mouth; worsening the pain. 

FURTHER READING 

Forouhi, Nita G. “Consumption of Hot Spicy Foods and Mortality—Is Chilli Good for Your Health?” BMJ: British Medical Journal, vol. 351, 2015. JSTOR, www.jstor.org/stable/26522622. Accessed 4 Jan. 2021.

BIBLIOGRAPHY 

[1] TEDEducation. “The Science of Spiciness - Rose Eveleth.” YouTube, YouTube, 10 Mar. 2014, www.youtube.com/watch?v=qD0_yWgifDM. 

[2] Green, Barry. “Why Is It That Eating Spicy, ‘Hot’ Food Causes the Same Physical Reactions as Does Physical Heat (Burning and Sweating, for Instance)?” Scientific American, Scientific American, 21 Oct. 1999, www.scientificamerican.com/article/why-is-it-that-eating-spi/. 

[3] Ji, Yue, et al. “Chemical Composition, Sensory Properties and Application of Sichuan Pepper (Zanthoxylum Genus).” Food Science and Human Wellness, vol. 8, no. 2, 2019, pp. 115–125., doi:10.1016/j.fshw.2019.03.008. 

[4] Team, The Alimentarium. “The Scoville Scale.” Alimentarium, Alimentarium, 23 July 2019, www.alimentarium.org/en/magazine/infographics/scoville-scale. 

[5] Bode, Ann M., and Zigang Dong. “The Two Faces of Capsaicin: Figure 1.” Cancer Research, vol. 71, no. 8, 2011, pp. 2809–2814., doi:10.1158/0008-5472.can-10-3756. 

[6] “Why Does Drinking Milk Ease the Pain of Eating Spicy Food?” Psychology Today, Sussex Publishers, 16 Feb. 2017, www.psychologytoday.com/us/blog/brain-babble/201702/why-does-drinking-milk-ease-the-pain-eating-spicy-food. 

[7] McCallum, Katie. “How To Cool Your Mouth Down After Eating Spicy Food.” Houston Methodist On Health, 28 Sept. 2020, www.houstonmethodist.org/blog/articles/2020/sep/how-to-cool-your-mouth-down-after-eating-spicy-food/.