Food scientists and researchers from Stellenbosch University (SU) and the Sapienza University of Rome have proactively developed a quick and user friendly method that South African producers and distributors of honey can use to detect whether the products they are selling is the real thing or not.
A recent article in the international journal Food Control explains how near-infrared (NIR) spectroscopy can be used to test South African honey. Laboratory and portable NIR instruments were calibrated specifically with South African honey in mind.
Because portable and mobile NIR instruments are available on the market, it would be possible to perform the tests on site at for instance a honey producer or distribution plant on calibrated equipment.
The specific NIR calibration for South African honey was developed by lead author Dr Anina Guelpa, as part of her postdoctoral research work in the Department of Food Science at SU and the University's Central Analytical Facility (CAF) CT-Scanner Facility. Dr Guelpa was assisted in developing and testing the method for South African conditions by her supervisor, NIR spectroscopy expert Prof Marena Manley of the SU Department of Food Science, SU researchers Dr Anton du Plessis and Dr Ruhan Slabbert, and Dr Federico Marini of the Sapienza University of Rome in Italy.
According to the records of the South African Beekeeping Industry, 1500 tons of honey is produced locally every year. It is however not enough to meet consumer demand, and therefore roughly the same volume is imported every year – at a lower price than that of locally produced honey.
Because honey is a high-value foodstuff, it has unfortunately become a target for adulteration and subsequent food fraud in many parts of the world. Whether it occurs in South Africa, and if so the extent of it, is not known.
In some parts of the world, cheap sugar syrups are sometimes added to honey being sold. Another form of misconduct may occur when honey is labelled as being produced locally, but in reality it has been imported or diluted with imported honey.
"Not only will the consumer be misled in the process, but it means that the local producers cannot compete with the low pricing of these adulterated honeys," says Prof Manley.
"There was therefore a need for a fast, non-destructive, easy to use and low cost classification method to detect potential adulteration in South African honey," she explains the reasoning behind the study.
Current methods to detect adulterated honey, such as the use of stable carbon isotopic ratio mass spectrometry (SCIRA) or thermal analysis, are expensive, time-consuming and in most cases destroy the sample used.
The researchers decided to proactively develop an NIR spectroscopy method with which to test the authenticity of South African honey.
The research team decided on NIR spectroscopy, because the technique has been used before in international studies to determine the floral origin of honey, or to authenticate its geographic or botanical origin.
By developing calibrations using the spectral information of honey of South African origin, it was possible for Dr Guelpa to verify whether samples are indeed produced by South African bees or not. The test can also pick up whether any sugars (such as glucose or fructose) or non-South African honey are added to a sample. This is possible even in cases where only a little bit of extra sugar has been added.
"Authentic South African samples, despite coming from diverse regions and having been made from pollen from different types of flowers, share specific spectroscopic characteristics that helps to differentiate them from imported and adulterated honeys," explains Prof Manley.
She says the technique could potentially also be used to distinguish between different types of South African honey (for instance bluegum of fynbos). Other advantages are that NIR measurements can be done quickly, it is non-invasive and is easy to perform.
Because the samples tested are not destroyed in the process, these can be stored as evidence in further investigations.
Reference: Guelpa, A. et al (2017). Verification
of authenticity and fraud detection in South African honey using NIR
spectroscopy, Food Control, 73, 1388-1396.
What is NIR spectroscopy?
Near-infrared (NIR) spectroscopy is technology that uses the NIR part (800 to 2500 nanometres) of the electromagnetic spectrum and used in NIR spectrophotometers.
How does it work?
• A sample of what is to be tested (such as honey, oil or wheat) is placed in an NIR spectrophotometer. (No prior preparation is needed – the sample can be used as is. This means that for instance in the case of wheat it does not have to be ground, and the whole kernels can be investigated as is.)
• A simple halogen light beam emits a harmless light (including the NIR region), and hits the sample.
• The light beam loses energy because it is partially absorbed by the sample. The amount of light being absorbed depends on the physical and chemical composition of each sample.
• The spectrophotometer measures the remaining light that is reflected. The lost (or absorbed) light is seen as unique spectral information which is specific to a sample. Each type of sample therefore has its own spectral information.
• The spectral images of for instance South African honey look the same at first glance. However, with the help of already developed calibrations it is possible to differentiate between honey that is from South African and honey that is not. In a similar way, the protein and moisture contents of different wheats can for example be measured simultaneously from a single sample.