A new lab method elaborated in a joint research by Semmelweis University and the Hungarian University of Agriculture and Life Sciences has not only proved successful at identifying changes induced by heating honey, but can serve as an alternative to existing analytical methods to distinguish other types of honey adulterations.

The researchers set out to find more accurate ways to verify manipulations of honey related to heating, origin or other types of adulteration. In their study, they compared two methods; near infrared spectroscopy (NIRS) and electronic tongue (ET), separately and in combination, to see their performance in detecting heat treatment of honey.

Honey is frequently heated to ease processing/packaging, often unknown to consumers. Heating above a certain temperature range (especially above 50°C) may deteriorate the quality of honey (alter taste, color, damage vitamins and antioxidants, etc.) and modify its composition, thus can be regarded as adulteration.

Our goal was to ultimately be able to distinguish between honey types and between genuine and adulterated honeys

says Zsanett Bodor, college senior lecturer at the Department of Dietetics and Nutritional Sciences at Semmelweis University, first author of the study.

Acacia, sunflower and false indigo honeys were heated at different temperatures (40-100 ◦C) for different lengths of time (60-240 min). While both ET and NIRS have been able to discriminate the majority of heated samples from the controls, their combination proved to be the most efficient: the model of the fused dataset provided >98% average correct classification of the sample groups and 100% correct classification of the control honeys. This is the first time that electronic tongue and NIR have been applied in combination for such aims.

Heating honey – an (unintentional) way of food fraud

Heating honey within a certain temperature range (up to 40 ◦C, this temperature being similar to hive’s own temperature) is allowed. However, heat treatment is necessary in some cases for easier handling and packaging of honey. Thus, it is not uncommon that manufacturers heat honey above 40 ◦C, or to much higher temperatures. Higher heat damages the composition of honey: color, taste, heat sensitive vitamins and antioxidants, composition can change. Heating also contributes to the formation of some unwanted compounds such as hydroxymethyl furfural (HMF). Detection of heat treatment is not easy, especially after exposition to lower temperatures or time periods.

The methods above also have a potential in revealing other types of honey mistreatment.

Honey is among the most adulterated foods in the world. Manufacturers either dilute genuine honey with syrups derived from plants or directly feed bees with them in the collection period.

Depending on the type of plant photosynthesis, some syrups, for example rice syrup, are harder to detect with the existing tools. Analysis based on the principal components of honey (such as moisture, pH, electrical conductivity, etc.) can only reveal larger deviations in concentrations (10%-20%-50%), but this highly depends on the type of honey, syrup and the method applied.

The researchers mixed sugar syrups of different types and concentrations into several types of honey, and then examined the samples using both methods. “We focused on lower concentrations (3-10%), which in general are difficult to detect,” explains Csilla Benedek, college associate professor at the Department of Dietetics and Nutrition at Semmelweis University, corresponding author of the study.

The electronic tongue (ET) easily detected a sugar syrup concentration of 10%, while near infrared spectroscopy (NIRS) was able to separate fake honeys from authentic honeys in almost every case, especially at sugar syrup concentrations of 5% and 10%

, she adds.

Compared to reference analytical methods determining physicochemical properties, ET and NIRS are more rapid. They need less reagents and are less laborious.

The two rapid techniques – especially if applied together – could provide a useful tool in the recognition of heat treatment of honeys with a better accuracy compared to the commonly used physicochemical methods.

They can also serve as an alternative to identify other types of manipulations. In order for these techniques (ET, NIRS) to become more efficient, a larger reference dataset has to be created.

Photo: Semmelweis University – Bálint Barta, illustration: iStock