By HVN’s Chief Scientist, Professor Richard Mithen
An illustration from the 14th Century of a European merchant sourcing black pepper in southern India, from Marco Polo’s Livre des merveilles. The desire for spices such as black pepper drove European exploration, colonialism and empire building.
No one knows precisely when the dried fruit of Piper nigrum was first ground up and used to make black pepper to season food. It may have been several thousand years ago in the southwest part of India, known today as Kerala, where this Piper vine is native.
Maritime traders from Indonesia would have been the first to introduce black pepper from India into China, the Middle East and North Africa, and thence into the Greco-Roman world where black pepper was greatly valued.
Subsequently, trade routes from India to Europe were dominated by traders of the Aksumite Empire of North Africa and the Arabian Peninsula and latterly, especially after the rise of Islam, by Arab traders. Much of this trade would have been through the lost ancient city and port of Muziris, situated somewhere on the Malabar coast, the precise location of which is still being sought by archaeologists.
All of this changed with the Crusades. The European demand for pepper and a small number of other spices, notably cloves and nutmeg, was insatiable. The spice trade drove the development of maritime technology, which led to the European Age of Exploration, and thenceforth, to imperialism and colonialism. While black pepper no longer drives global trade, it remains the world’s most traded spice.
Piper nigrum is a member of the plant family Piperaceae, which includes over 2,000 species within the genus Piper. Several of these Piper species have become cultivated for their spicy seeds, while the leaves, fruits and seeds of other Piper species are regularly collected from wild populations and have become part of traditional cuisines and used as therapeutics.
These Piper species include the New Zealand endemic Piper excelsum, or kawakawa, a species of considerable cultural importance to Māori and considered Taonga. Piper species contain the alkaloid piperine, which is the main compound that provides the ‘hot and spicy’ sensation when eaten. Kawakawa also contain many other compounds that contribute to their distinct aromas and flavours, and notably myristicin and elemicin, which are also found in nutmeg.
Piper nigrum – black pepper.
The English word ‘pepper’ is derived from the Latin piper, and in turn from the Sanskrit pippali, which probably referred to a small number of cultivated Piper species in India including ‘long pepper’, Piper longum. The dried fruits of these spices are somewhat hotter than black pepper (they probably contain more piperine) and were used primarily as a medication rather than a spice. It was widely traded in antiquity.
The rise of the European trade in spices led to these peppers being displaced by black pepper, and following the influx of new foods from the Americas in the 16th Century. It was further displaced by the fruits of Capsicum annum, which we know as ‘chili peppers’ – ‘chili’ being the name for these fruits from the Nahuatl language spoken by the native people of central America at the time of the Spanish conquest, and ‘pepper’ due to the similarity in taste and maybe the shape of the fruits to that of the long pepper. Chili peppers belong to the potato family (the Solanaceae), a family unrelated to the Piperaceae, and accumulate another alkaloid known as capsaicin.
The name ‘pepper’ having first migrated from Piper to Capsicum is now associated with plants in other unrelated plant families. The mustard family (Brassicaceae) have many species that are often described as ‘peppery’ including rocket (Diplotaxis and Eruca species), pepper cress (Lepidium species) and watercress (Rorippa species), and some species that have a much hotter taste, such as wasabi (Eutrema japonicum) and horse radish (Armoracia rusticana). The peppery and hot flavours of these plants are not due to alkaloids, but unrelated compounds known as isothiocyanates, sometimes called mustard oils.
In New Zealand, mountain pepper or horopito (Pseudowintera colorata) is from yet another family, the Winteraceae, which is found throughout the southern hemisphere. The ‘hot’ flavour in horopito comes from another type of compound – a sesquiterpene known as polygodial.
Wasabi, chili peppers, horopito and kawakawa all belong to different plant families and have different leaf chemistry, but all impart a ‘hot’ sensation that we like in moderation due to the stimulation of the TRVP1 pain receptor.
How do these diverse plants with diverse chemistries all impart a more-or-less hot or burning sensation? This puzzle was solved by the American physiologist Professor David Julius, for which he won the Nobel Prize for Physiology and Medicine in 2021 together with the molecular biologist Ardem Patapoutian.
Those in New Zealand will be able to hear Professor Julius speak as Key Guest Speaker at Queenstown Research Week 2023.
Julius identified and characterised pain receptors that detect heat and cold, the most prominent of which is the TRVP1 ‘capsaicin’ receptor. These receptors enable us to sense heat and cause us to feel pain. Julius showed that in addition to heat, compounds such as capsaicin interact with TRVP1 receptors so that we feel a burning sensation – but of course no burning is actually occurring, we have been fooled by the plant. Likewise, piperine from black pepper and kawakawa also activates TRPV1. Isothiocyanates from Brassicaceous plants such as wasabi and polygodial predominantly activated a related pain receptor TRPA1, in addition to TRVP1.
Following the interaction of capsaicin and other agonists with TRVPI and the excitation of neurons that transmit the electrical signals to our brain causing the burning sensation, the receptors can become desensitised, so that further stimulation does not result in any additional painful sensations, whether exposed to capsaicin or other agonists. This has led to capsaicin being used as an analgesic.
Plants have used these compounds to hijack our pain receptor pathways as a defence mechanism to deter herbivores feeding on their leaves. We and other herbivores literally feel our mouths are ‘on fire,’ and soon stop eating. Plants need to make some compromises as they often rely on birds to distribute their seeds. It is quite a familiar sight to see native tui and exotic blackbirds feasting on the fruits of kawakawa, and birds will also eat homegrown chili peppers. The phenomenon was also solved by Julius who demonstrated that while the avian TRVP1 can detect noxious heat, unlike the mammalian receptors they are not sensitive to capsaicin . There would appear to be an evolutionary ‘fine tuning’ interaction between the defence compounds in plants and the pain receptors of herbivores to allow for selective herbivory and the distribution of seeds.
Thousands of years ago, native peoples in different parts of the world found that they liked a little bit of heat in their food, and domesticated chili peppers in the Americas, Piper species in India, Zanthoxylum species in China (Sichuan Pepper), wasabi in Japan, and watercress and other Brassicaceous species in Europe. All of which can be purchased in New Zealand supermarkets to spice up our dinners.
Māori also discovered that native plants of Aotearoa New Zealand can give a little heat. While kawakawa and horopito are the most well-known, the native species of the mustard family nau (Lepidium species) and matangoa (Rorippa divarcata) have also been gathered and eaten, although they have now become rare.
What a treat it would be to go into one of those supermarkets and purchase a salad bag of matangoa (instead of exotic watercress), buy a refill for the pepper grinder of dried kawakawa fruits (instead of those of black pepper), and to find a small bag of horopito leaves (as opposed to a bag of red chili peppers) to flavour our curries. It would surely be an Aotearoan feast for our TRVP1 and TRPA1 pain receptors ….
 The Aksumite Empire dominated trading routes between India and Rome from the 4th Century BP for about 400 years, with the use of Greek and a lingua franca. It adopted Christianity in the 4th Century, and the ancient church of Lady of Zion in the capital city Axum in the present Tigray region of Ethiopia is reputed to house the Ark of the Covenant. The empire collapsed in the 10th Century partly due to the rise of Arab traders.
 The fabled port of Muziris was referred to by Greek and Roman writers, including Pliny. It was the major export port for black pepper from India to North Africa and the Mediterranean. It appears to decline from the 9th Century, and its precise location is not known, although excavations in the current city of Kodungallur may suggest it is the site of the ancient port.
 The largest producer of black pepper today is Vietnam, with 36% of the world’s production.
 Piper excelsum G.Forst is also known as Macropiper excelsum (G.Forst) Miq.
 Alkaloids are organic compounds that contain nitrogen. Many naturally occurring alkaloids have important medical uses such as, morphine, atropine and quinine, while others are used as drugs, such as caffeine, nicotine and cocaine.
 Jayaprakash et al (2023). Exploring the Chemical Space of Kawakawa Leaf ( Piper excelsum). Nutrients 5;14(23):5168. doi: 10.3390/nu14235168.
 Unlike black pepper, the individual fruits of long pepper remain together in an infructescence similar to the immature fruits of kawakawa, and appearing somewhat similar in shape to a small chili pepper.
 Polygodial is also found within the water pepper of Polygonium hydropiper, from which the name is derived. It is a native plant of Europe and Asia with a history of use as an alternative to black pepper.
 The Nobel prize was awarded for Julius’s research on how we sense heat and cold, and Patapoutian’s research on how we sense touch. Anon (2021). Medicine Nobel Prize for duo who discovered biology of senses. Nature 598 14th Oct 2021.
 Jordt and Julius (2008). Molecular basis for sensitivity to “hot chili peppers”. Cell 108(3) 421-30.