What makes chilli peppers so spicy and how do they help with pain relief? The SCI Horticulture Group explained all ahead of their appearance at BBC Gardeners’ World Live in Birmingham from 16-19 June.
This June, the SCI Horticulture Group will tell the public all about the hidden chemistry behind their favourite fruit and vegetable plants. One of the main plants they will feature at the National Exhibition Centre is the humble chilli pepper – and these famous fruit-berries conceal more secrets than you might think…
The chilli pepper (Capsicum spp.) is a member of the Solanaceae, the plant family that includes edibles such as potatoes, tomatoes, aubergines, but also poisonous plants such as tobacco, mandrake, and deadly nightshade.
The chilli was brought to Europe in the 15th century by Christopher Columbus and his crew. They became acquainted with it on their travels in South and Central America and, shortly thereafter, to India via the Portuguese spice trade.
Of the 42 species in the capsicum genus, five have been domesticated for culinary use. Capsicum annuum includes many common varieties such as bell (sweet) peppers, cayenne and jalapenos. Capsicum frutescens includes tabasco. Capsicum chinense includes the hottest peppers such as Scotch bonnet. Capsicum pubescens includes the South American rocoto peppers, and capsicum baccatum includes the South American aji peppers.
From the five domesticated species, humans have bred more than 3,000 different cultivars with much variation in colour and taste. The chilli and bell peppers that we eat are the fruit – technically berries – that result from self-pollination of the flowers.
>> The SCI Horticulture Group brings together those working on the wonderful world of plants.
Today, chilli peppers are a global commodity. In 2019, 38 million tonnes of green chilli peppers were produced worldwide, with China producing half of the total. Spain is the largest commercial grower of chillies in Europe.
Capsaicin helps give chilli peppers their heat
Capsaicin is the main substance in chilli peppers that provides the spicy heat. It binds to receptors that detect and regulate heat (as well as being involved in the transmission and modulation of pain), hence the burning sensation that it causes in the mouth.
In humans, these receptors are present in the gut as well as the mouth (in fact, throughout the peripheral and central nervous systems) – hence the after-effects of eating too much chilli. Capsaicin, however, is not equally distributed in all parts of pepper fruit. Its concentration is higher in the area surrounding the seeds.
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The Scoville Heat Unit Scale is used to classify the strength of chilli peppers. Scoville heat units (SHU) were named after American pharmacist Wilbur Scoville who devised a method for rating chilli heat in 1912.
The ludicrously hot Dragon’s Breath chilli
This method relied on a panel of tasters who diluted chilli extract with increasing amounts of sugar syrup until the heat became undetectable. The greater the dilution to render the sample’s heat undetectable, the higher the SHU rating. Pure capsaicin measures 16,000,000 SHU.
The capsaicin content of chilli peppers varies wildly, as is reflected in the SHUs of the peppers below:
The seeds of chillies are dispersed in the wild by birds who do not have the same receptors as mammals and, therefore, are unaffected by capsaicin. Perhaps chillies have evolved to prevent mammals from dispersing their seeds?
Capsaicin has also been shown to protect the plant against fungal attack, thus helping the fruit to reach maturity and the seeds to be dispersed before succumbing to rot. This antifungal property can also be put to good use in helping to preserve foods for human consumption.
Capsaicin was pivotal in the research that led to the award of the 2021 Nobel Prize in physiology and medicine to David Julius and Ardem Patapoutian for their discoveries of receptors for temperature and touch.
The two US-based scientists received the accolade for describing the mechanics of how humans perceive hot, cold, touch, and pressure through nerve impulses. The research explained at a molecular level how these stimuli are converted into nerve signals, but the starting point for the study was work with capsaicin from the humble chilli pepper.
Capsaicin is used as an analgesic (a pain reliever) in topical ointments, nasal sprays, and patches to relieve chronic and neuropathic pain. Clinical trials continue to investigate the potential of capsaicin for a wide range of additional pain indications and as both an anti-cancer and anti-infective agent.
>> Special thanks to Neal Price from Chillibobs, Martin Peacock of ZimmerPeacock, Hydroveg, and The University of Reading Soft Fruit Technology Group for supporting the work of the SCI Horticulture Committee at BBC Gardeners’ World Live.
>> Our resident gardening expert, Geoff Dixon, provides plenty of gardening tips on the SCIBlog.
How do green spaces, gardens as well as fruit and vegetables impact our health and wellbeing? Professor Geoff Dixon tells us more.
‘We are what we eat’ is an aphorism that is becoming much better understood both by the general public and by healthcare professionals. Similarly, ‘we are where we live’ is gaining greater appreciation. Both these pithy observations underline the social and economic importance of horticulture and the allied art of gardening.
An exuberant display of flowers – what can be better for the soul?
Few things stimulate the human spirit more than a fine, colourful display of well grown and presented flowers. Seeing and working with green and colourful plants is increasingly recognised for its psychological power, reducing stress and increasing wellbeing. In our increasingly urbanised society, with myriads of high-rise housing blocks, the provision of well-tended parks and gardens is not a luxury – it is essential.
Hospital patients recover more quickly when they can see and sit in green spaces. Equally, providing access to gardens and gardening for schools should be a vital part of the children’s environment. They gain an understanding of biological mechanisms and the equally important need for conserving biodiversity and controlling the rate of climate change.
The recently published National Food Strategy emphasised the importance of fruit and vegetables as a major part of our diets. Both fruit and vegetables provide essential vitamins, nutrients and fibres which consumed over time diminish the incidence of cancers, coronary, strokes and digestive diseases.
Apricots are high in catechins.
Eating varying types of fruit and vegetables increases their value – apricots, for example, are high in catechins which are potent anti-inflammatory agents. Members of the brassica (cabbage) family are exceptionally valuable for mitigating diseases of ‘modern society’. All contain glucosynolates, which evolved as means for combating pest and pathogen attacks and co-incidentally provide similar services for humans. Watercress – an aquatic brassica – is rich in vitamins A, C and E, plus folate, calcium and iron. Its high water content means portions consumed fresh or as soups are low in calories.
Watercress – an aquatic brassica boasts numerous health benefits.
These messages and facts are now being recognised both publicly and politically, and not before time. For the past 50 years the universal panaceas have been pharmaceutical drugs. In moderation, these have been of immense value. Use to excess is both counterproductive and needlessly expensive health-wise and financially.
Returning to Grandma’s advice, ‘an apple a day keeps the doctor away’, supports both individual and planetary good health.
Written by Professor Geoff Dixon, author of Garden practices and their science, published by Routledge 2019.
Crop rotation, seaweed extracts, lime, and a range of organic materials can all improve soil health and crop yields. Professor Geoff Dixon shows you several ways to improve your soil.
Rapidly rising costs of living are affecting all aspects of life. Increasing costs of fertilisers are affecting food production, both commercially and in gardens and allotments.
Wholesale prices of fertilisers have jumped four-fold from £250 to £1,000 per tonne within six months. All forms of garden fertilisers are now much more expensive. Crops, especially vegetables, only thrive if provided with adequate nutrition (see nitrogen-deficient lettuce below). Consequently, fertiliser use must become more efficient.
Nitrogen deficiency in lettuce.
Healthy, fertile soils achieved through good management are key to this process. That ensures roots can take up the nutrients needed in quantities that result in balanced, healthy growth.
Soil pH is a major regulator of nutrient availability for roots. Between pH 6.5 to 7.5, the macro nutrients, nitrogen, phosphorus, and potassium are fully available for root uptake. Below and above these values, nutrient absorption becomes less efficient.
>> How much soil cultivation do you need for your vegetables? Find out more in Prof Dixon's blog on cultivation.
As a result, soluble nutrients are wasted and washed by rainfall below the root zones. Acidic soils can be improved by liming in the autumn. Sources of lime derived from crushed limestone require up to six months to cause changes in soil pH values. Lime should be used in ornamental gardens with caution as it can result in micronutrient deficiencies.
Iron deficiency in wisteria.
Soil health and fertility are greatly increased by adding organic materials such as farmyard manure and well-made composts. Increasing soil carbon content helps mitigate climate change while raising fertiliser use efficiencies.
Beneficial soil biological life such as earthworms, insects, benign bacteria and fungi are greatly encouraged when you increase soil humus content. Using crop rotations, which include legumes, raises natural levels of soil nitrogen. This is a result of legumes’ symbiotic relationships with nitrogen-fixing bacteria.
Leafy vegetables such as brassicas require large amounts of nitrogen and, hence, should follow legumes in a rotation. Avoiding soil compaction encourages adequate aeration, benefiting root respiration and providing oxygen for other organisms.
Organic materials are of great value in ornamental gardens when applied as top dressings in late autumn or early spring. This provides two benefits: a slow release of nutrients into the root zones as decomposition occurs, and prevention of weed growth.
Inorganic fertiliser use can be further minimised by using proprietary seaweed extracts. These contain macro- and micro-nutrients plus several natural biostimulant compounds that aid healthy ornamental plant growth and flowering (illustration no 3 rose Frűhlingsgold).
Written by Professor Geoff Dixon, author of Garden practices and their science.
Broad beans are an undemanding and valuable crop for all gardens. Probably originating in the Eastern Mediterranean and grown domestically since about 6,000BC, this plant was brought to Great Britain by the Romans.
Header image: a rich harvest of succulent broad beans for the table
Capable of tolerating most soil types and temperatures they provide successional fresh pickings from June to September. Early crops are grown from over-wintered sowings of cv Aquadulce. They are traditionally sown on All Souls Day on 2 November but milder autumns now cause too rapid germination and extension growth. Sowing is best now delayed until well into December. Juicy young broad bean seedlings offer pigeons a tasty winter snack, consequently protection with cloches or netting is vital insurance.
From late February onwards dwarf cultivars such as The Sutton or the more vigorous longer podded Meteor Vroma are used. Early cropping is promoted by growing the first batches of seedlings under protection in a glasshouse. Germinate the seed in propagating compost and grow the resultant seedlings until they have formed three to four prominent leaflets. Plant out into fertile, well-cultivated soil and protect with string or netting frameworks supported with bamboo canes to discourage bird damage.
Young broad bean plants supported by string and bamboo canes
More supporting layers will be required as the plants grow and mature. Later sowings are made directly into the vegetable garden. As the plants begin flowering remove the apical buds and about two to three leaves. This deters invasions by the black bean aphid (Aphis fabae). Winged aphids detect the lighter green of upper foliage of broad beans and navigate towards them!
Allow the pods ample time for swelling and the development of bean seeds of up to 2cm diameter before picking. Beware, however, of over-mature beans since these are flavourless and lack succulence. Broad beans have multiple benefits in the garden and for our diets. They are legumes and hence the roots enter mutually beneficial relationships with nitrogen fixing bacteria. These bacteria are naturally present in most soils. They capture atmospheric nitrogen, converting it into nitrates which the plant utilises for growth. In return, the bacteria gain sources of carbohydrates from photosynthesis.
Broad bean root carrying nodules formed around colonies of nitrogen fixing bacteria
Broad beans are pollinated by bees and other beneficial insects. They are good sources of pollen and nectar, encouraging biodiversity in the garden. Nutritionally, beans are high in protein, fibre, folate, Vitamin B and minerals such as manganese, phosphorus, magnesium and iron, therefore cultivating healthy living. Finally, they form extensive roots, improving soil structure, drainage and reserves of organic nitrogen. Truly gardeners’ friends!
Professor Geoff Dixon, author of Garden practices and their science (ISBN 978-1-138-20906-0) published by Routledge 2019.
More people are looking at their nutritional intake, not only to improve wellbeing but also reduce their environmental impact. With this, comes a move to include foods that are not traditionally cultivated or consumed in Europe.
Assessing whether this growing volume of so called ‘novel foods’ are safe for human consumption is the task of the European Food Safety Authority. The EFSA points out, ‘The notion of novel food is not new. Throughout history new types of food and food ingredients have found their way to Europe from all corners of the globe. Bananas, tomatoes, tropical fruit, maize, rice, a wide range of spices – all originally came to Europe as novel foods. Among the most recent arrivals are chia seeds, algae-based foods, baobab fruit and physalis.’
Under EU regulations any food not consumed ‘significantly’ prior to May 1997 is considered to be a ‘novel food’. The category covers new foods, food from new sources, new substances used in food as well as new ways and technologies for producing food. Examples include oils rich in omega-3 fatty acids from krill as a new source of food, phytosterols as a new substance, or nanotechnology as a new way of producing food.
Providing a final assessment on safety and efficacy of a novel food is a time consuming process. At the start of 2021 the EFSA gave its first completed assessment of a proposed insect-derived food product. The panel on Nutrition, Novel Foods and Food Allergens concluded that the novel food dried yellow meal worm (Tenebrio molitor larva) is safe for human consumption.
Dried yellow meal worm (Tenebrio molitor larva) is safe for human consumption, according to the EFSA.
Commenting in a press statement, as the opinion on insect novel food was released, Ermolaos Ververis, a chemist and food scientist at EFSA who coordinated the assessment said that evaluating the safety of insects for human consumption has its challenges. ‘Insects are complex organisms which makes characterising the composition of insect-derived products a challenge. Understanding their microbiology is paramount, considering also that the entire insect is consumed,’
Ververis added, ‘Formulations from insects may be high in protein, although the true protein levels can be overestimated when the substance chitin, a major component of insects’ exoskeleton, is present. Critically, many food allergies are linked to proteins so we assess whether the consumption of insects could trigger any allergic reactions. These can be caused by an individual’s sensitivity to insect proteins, cross-reactivity with other allergens or residual allergens from insect feed, e.g. gluten.’
EFSA research could lead to increased choice for consumers | Editorial credit: Raf Quintero / Shutterstock.com
The EFSA has an extensive list of novel foods to assess. These include dried crickets (Gryllodes sigillatus), olive leaf extract, and vitamin D2 mushroom powder. With the increasing desire to find alternatives to the many foods that we consume on a regular basis, particularly meat, it is likely that the EFSA will be busy for some time to come.