UOA08-04: Measuring chilli heat with electrochemistry
Submitting InstitutionUniversity of Oxford
Unit of AssessmentChemistry
Summary Impact TypeTechnological
Research Subject Area(s)
Chemical Sciences: Physical Chemistry (incl. Structural), Other Chemical Sciences
Summary of the impact
Richard Compton's group at the University of Oxford has developed an
electrochemical sensor which uses multi-walled carbon nanotube electrodes
to detect capsaicin molecules and related capsaicinoids — the chemicals
responsible for the hot taste of chilli peppers. The technology, patented
in 2008, has been licensed to the English Provender Company, which uses
the sensors to perform quality assurance on 10 tonnes of incoming chillies
every month, as well as monitoring reproducibility of finished products.
In February 2013 Singapore-based Bio-X obtained an exclusive licence for
the patent in Asia to develop, build and sell devices on a global basis.
The science behind the technology has been the subject of significant
outreach activities at UK schools, and has attracted extensive media
The `heat' or piquancy of chillies is a result of the molecule capsaicin
(8-methyl-N-vanillyl-6-nonenamide) and related compounds called
capsaicinoids. Chillies are used ubiquitously throughout the food
industry, and in order to ensure consistency there is a need to assess
chilli strength — or, more technically, capsaicin content. Such
measurements are traditionally performed using organoleptic (taste)
testing: chilli pepper extract is diluted in sugar solution until the
`heat' is no longer detectable to a panel of five tasters. The degree of
dilution gives a measurement on the Scoville scale, which dates back to
1912, and yields numbers which range from 0 to 16,000,000. By means of
illustration, a Jalapeno pepper scores 2,500, Tabasco sauce 30,000-50,000,
and pure capsaicin 16,000,000. The Scoville test can give accurate results
when performed by expert tasters. However results are entirely dependent
on the capsaicin sensitivity of the tasters, and the test is
time-consuming and costly to perform since it requires a panel of five
experts for every measurement of chilli heat. More consistent scientific
methods of measuring capsaicin content involve cumbersome and expensive
high-performance liquid chromatographs, which also require trained staff
and involve time for sample preparation and results analysis.
In the mid-2000s Richard Compton and colleagues in the Department of
Chemistry, University of Oxford began to undertake fundamental studies of
adsorptive stripping voltammetry (AdSV) at multiwalled carbon nanotube
modified basal plane pyrolytic graphite electrodes (MWCNT-BPPGE) —
electrodes coated in carbon nanotubes. The Compton group applied the
technique to a variety of analytes; with paracetamol  they obtained a
detection limit of 10 nM, almost certainly the lowest limit of detection
thus far reported for paracetamol using electrochemical techniques,
showing that the technique was extremely sensitive. In a similar study on
4-hexylresorcinol (an anaesthetic and antiseptic used in pharmaceutical
products) , Compton and colleagues experimented with MWCNT-BPPGE
modified screen-printed electrodes, thereby demonstrating that the AdSV
technique could easily be incorporated into a simple and inexpensive
Compton and colleagues also studied food anayltes, specifically capsaicin
molecules, which they observed to spontaneously adsorb onto a MWCNT-BPPGE.
Further, when the voltage at the electrode was adjusted appropriately, the
molecules were oxidised and stripped from its surface. This finding led to
the development of an AdSV technique which built on the fact that, if
deposition and stripping conditions were kept constant, the process could
be calibrated to link the voltammetric stripping current to solution
concentration . The Compton group then developed an innovative
electrochemical technique to reliably quantify the concentration of
capsaicin in a sample.
The technique was refined by the group so that the multi-wall carbon
nanotube-based electrode could be screen-printed and used with a hand-held
sensor to assess capsaicin concentration outside the laboratory. To use
the device, food extracts containing chilli are diluted in a ratio of
1:100 with 0.05M Britton-Robinson buffer at pH 1.0 and then placed on the
carbon nanotube electrode. The voltage is scanned, and the variation in
voltammetric stripping current is recorded. The result is then converted
into a measurement corresponding to the Scoville scale. The technology was
patented in 2008 by Isis Innovation Ltd, the University of Oxford's
technology transfer division .
The Compton group also developed a similar electrochemical technique
using carbon-based electrodes to measure the strength of garlic by
identifying the presence of disulfides . This technology was patented
in the UK, and by Isis Innovation, in 2010 .
Richard Compton has been on the academic staff of the Department of
Chemistry from 1985 to the present day.
References to the research
Asterisked outputs denote best indicators of quality; University of
Oxford authors are underlined.
1. Kachoosangi, R.T., Wildgoose, G.G., Compton, R.G.
Sensitive adsorptive stripping voltammetric determination of paracetamol
at multiwalled carbon nanotube modified basal plane pyrolytic graphite
electrode. Analytica Chimica Acta 2008, 618, 54-60. DOI:
2. Kachoosangi, R.T., Wildgoose, G.G., Compton, R.G.
Adsorptive stripping voltammetric determination of 4-hexylresorcinol in
pharmaceutical products using multiwalled carbon nanotube based
electrodes. Electroanalysis 2008 20, 1714-1718. DOI:
3. * Kachoosangi, R.T., Wildgoose, G.G., Compton,
R.G. Carbon nanotube-based electrochemical sensors for quantifying
the 'heat' of chilli peppers: The adsorptive stripping voltammetric
determination of capsaicin. Analyst 2008,133, 888-895. DOI:
10.1039/b803588a This paper reports the analytical protocol employed
in the `chillimeter'.
4. * Kachoosangi, R.T., Wildgoose, G.G., Compton,
R.G. Chilli Sensor Patent, EP 09723101.3 , priority date 18 March
2008 (Isis Project 3670).
This patents the analytical procedure for the determination of
capsaicin via adsorptive stripping voltammetry using carbon nanotubes.
5. * Martindale, B. C. M., Aldous, L., Rees, N. V.,
Compton, R. G. Towards the electrochemical quantification of the
strength of garlic. Analyst 2011,136,128-133. DOI:
10.1039/c0an00706d This paper reports work stimulated by discussion
with the food technology industry into the electrochemical measurement
of garlic flavour.
Details of the impact
Following the patenting of the Compton group's chilli sensor technology
by Isis Innovation in early 2008, there were well over a hundred worldwide
media reports on the potential of the new technique in newspapers,
magazines, journals and online forums (including the Guardian, Nature, the
Royal Society of Chemistry News, many chemistry journals and specialist
chilli industry publications) . Interest focussed particularly on the
objectivity and precision of the measurements obtained, and on the greatly
reduced costs in contrast to the traditional method of using teams of
tasters [8, 9]. Isis Innovation prepared the chilli sensor project for
commercialisation, and the English Provender Company (EPC) subsequently
expressed an interest in the technology for commercial purposes. Using
EPSRC Pathway to Impact funds, prototypes were built and a PDRA employed
to assist with field trials. The Compton group showed EPC staff how to use
the tester on their food samples, and followed up with several visits to
monitor progress. Isis licensed the technology to EPC on a non-exclusive
basis in 2012 .
EPC, a company with a turnover of £ 63.6 M in 2012 and 323 employees
, produces a wide range of sauces and condiments for use in domestic
food, such as their Very Lazy range of pre-prepared ingredients, and is a
key supplier of ready meals for the UK's major food retailers. It makes
around 250 tonnes of cooked products (ready meals) each month containing
chilli, and approximately 200,000 jars of chilli-containing foods.
Typically it uses up to 10 tonnes of chillies every month, which vary
dramatically in heat; there is thus a need to ensure consistency in both
raw materials and finished product. Extensive tests by EPC in its
production facilities confirmed that Compton's electrochemical device was
accurate and reliable and matched Scoville Test results, a key part of
validating the device and convincing the industry to use the method.
Following this, EPC has routinely used the sensor as a quality assurance
monitor on the incoming raw ingredients. The company can now offer its
customers (which include Marks and Spencer, 2 Sisters Food Group and
Greencore Group) improved consistency in the products it delivers, and
this has been well received by the customers concerned . According to
the Head of Technical at EPC, `the device [chilli tester] has a
massive place in our future'.
In February 2013 the Singapore-based company Bio-X (S) Pte. Ltd. obtained
an exclusive licence for the chilli sensor patent in Asia-Pacific and a
non-exclusive licence in the rest of the world (again through Isis
Innovation). Bio-X works with technologies and products (including
chemical sensors) targeted at the measurement of spiciness in food, and
aims to establish standardisation for heat in the food industry. Following
licensing, Bio-X is designing and building a new commercially available
chilli sensor, and demonstration units have been sold prior to full-scale
launch. Nestlé have been involved in a trial in which data from Bio-X's
Chilli Tester matched with their own data from high performance liquid
chromatography — an extremely promising outcome [13, 14]. The CEO of Bio-X
has stated the advantages to them of the chilli sensor technology: `Both
suppliers and users of chillies can be assured of the quality by using a
simple handheld device. Initially, we expect to see the Chilli Tester
being used by food manufacturers to determine the quality of their raw
materials and chilli farms to grade their products — but the real
potential of the Chilli Tester will be realised in giving the consumer a
number that they can use in deciding on sauces and other food products.'
The science behind the chilli sensors has been the subject of significant
outreach activities at several UK schools. Since July 2012 a consortium of
seven Yorkshire schools, led by Shelley College in Huddersfield and also
involving the University of Huddersfield, has been engaged in an ongoing
collaboration and outreach programme with the Compton group, aimed at
increasing science applications from such students to research-intensive
universities. Students aged 14-15 have successfully used research-level
equipment based on the technology described in section 2 to investigate
capsaicin levels in fresh chillies and chilli products. They have also
used Compton's voltammetry techniques to investigate and quantify the
amount of ascorbic acid in supplements and soft drinks. The programme has
now expanded to incorporate a chilli-growing project, and selected
students have taken part in residential visits to Oxford. The links with
the GCSE chemistry curriculum are significant and include reinforcement of
topics such as atomic structure and bonding, ionic compounds, covalent
structures (carbon), electrolysis, redox reactions and nanoscience. In
practical terms the activities give students the chance to improve skills
in risk assessment, collection of data, processing and interpreting data,
and development of hypotheses and explanations. In addition it assists in
preparing them for aspects of the A level Chemistry syllabus, especially
in the topics identified above.
The Director of Science at Shelley College confirms that the programme is
encouraging more students to pursue chemistry seriously: `The students
from Shelley and the other schools involved in the project could not be
more enthusiastic about taking their [chemistry] studies further. The
whole nation recognises the importance of producing first class
scientists for the future and this project is helping to further that
aim in a way that should not be underestimated.' The outreach has
been supported by funds from St John's College and the Department of
Chemistry, University of Oxford, and from the Royal Society of Chemistry
A second schools programme started in early 2013 at Cheltenham Ladies
College in Gloucestershire, aided by a Partnership Grant from the Royal
Society. Again, with active support from the Compton group, students have
used the techniques described in the research section to devise their own
experiments investigating capsaicin levels within chilli plants (the
strength of dried versus fresh chillies, and which solvent will extract
capsaicin more readily). The College's Head of Chemistry feels the project
`has helped push science to the top of the school agenda. A significant
proportion of the school's cohort has become engaged with the project.'
In addition the Cheltenham students have particularly benefited from the
high proportion of female researchers from the Compton group visiting the
school, which has `served as an excellent motivator for young female
Over 100 students in all have so far taken part across the schools
involved, and both programmes are continuing.
Sources to corroborate the impact
- A full list of media sources which ran the chilli sensor story is held
May 2008 Nature News article detailing the advantages of the chilli sensor
technique and the chemistry behind it.
June 2008 article in the Guardian describing Compton's development of the
chilli sensor technique and its commercial potential.
- Isis Innovation can corroborate the details of the licence with the
English Provender Company and with Bio-X, details of patent-related income
for the University of Oxford, and quotes from the Bio-X CEO on the
benefits to them of the chilli sensor technology.
- Details of English Provender turnover 2012 at
- The Head of Technical at English Provender Company can corroborate the
use of the Chilli Meter in quality assurance of incoming raw materials,
and the importance placed on the device by the company and its customers.
- The Bio-X webpage at http://biox.com.sg/data-book/
confirms the link with the Compton research. The homepage shows the
chilli sensor: http://biox.com.sg/ .
- Bio-X June 2013 progress report to Isis Innovation (held on file),
corroborating progress towards a commercially-available chilli sensor, and
results of trials including the trial with Nestlé.
- 15. Letter from the Director of Science at Shelley College (held on
file), corroborating details of Compton group outreach activities and
impact on students.
- Email from the Head of Chemistry at the Cheltenham Ladies' College (held
on file), corroborating details of Compton group activities and impact on