Using NMR-based screening for quality and authenticity analysis

With food authenticity of growing concern, honey is one of the foods under increasing scrutiny and its production is now subject to a number of regulations designed to ensure authenticity and quality. Honey producers and quality control laboratories now require increasingly sophisticated methods of analysis. Here we explore how nuclear magnetic resonance (NMR) based screening provides a cost efficient, complete analysis, which can be used reliably to ensure the honey that reaches consumers is ‘exactly what it says on the tin’.

Honey production challenges
The rules and regulations surrounding the content, labeling and even the very nature of components within honey are the subject of growing debate. With numerous contested environmental, ecological and personal health issues to consider, modern honey manufacturers are faced with the challenge of meeting a host of variable regulations and ensuring consumer protection.

Honey is in high demand but low supply, and we have seen the number of adulterated products in the market rise sharply in recent years. Adulteration can include the addition of other sugars, such as high-fructose corn syrup, as well as the declaration of the wrong geographic region of origin, and is becoming much more difficult to detect.

The authentication of food products is of primary importance for both consumers and the food industry, spanning all levels of the production process. With a number of food scandals in recent years, the European Commission now encourages the use of analytical methods to determine the authenticity and quality of honey products. To beat the fraudsters, honey producers and quality control laboratories therefore require increasingly sophisticated methods of analysis. Here we explore how nuclear magnetic resonance (NMR) based screening provides a cost efficient complete analysis, covering all aspects related to authenticity, quality control and quantification.

The quality and authenticity of honey
Honey is defined as the natural sweet substance produced by honeybees and consists mainly of sugars, but also contains acids, minerals, vitamins and amino acids. The composition of honey is mostly dependent on its floral source, and this also enables the region of production to be determined.  The supply of honey is greatly influenced by fluctuations in weather, and this factor combined with the declining bee population and its high production cost, makes honey particularly susceptible to adulteration.

The addition of sweetening agents to a product labelled and sold as honey is both illegal and unethical. This is a form of economic adulteration as it is done for financial gain by decreasing the value of the product without notifying the buyer. This method is particularly damaging to the industry as a whole as it affects consumer opinion.

Due to the increasingly international nature of the food market, the import and export of honey has significantly increased over recent years. This extends concerns beyond domestic honey production and authenticity to issues of product quality and global quality standards. There is rising demand for international bodies and governments to intervene in the quality control of food products to protect the health and safety of consumers, particularly as some common honey adulterants, including gluten and beet sugar, are allergenics.

Analyzing honey – a new approach
There are several methods available for the determination of honey authenticity. However, many techniques provide insufficient sensitivity and poor selectivity when faced with complex food matrices, and so cannot be used to simultaneously determine authenticity and adulteration. Now, NMR can provide an efficient and cost-effective turnkey solution.

A development  from Bruker demonstrates how NMR may be used for comprehensive honey analysis. Using the new Honey Profiling module of the FoodScreener platform, both targeted and non-targeted analysis was conducted. This allowed for the simultaneous identification and quantification of a large number of compounds in one single measurement needing only one calibration standard.

Based on 400 MHz NMR spectroscopy, the principle relies on the acquisition of the spectroscopic fingerprint specific for each individual sample. This method has already proved successful for providing a sample type-specific and fully automated push button solution for fruit juice and wine, delivering reliable targeted and non-targeted multi-marker analyses with reduced cost per sample.

Using the NMR based technique on honey, it proved possible to identify and quantify more than 30 parameters, including proline, sucrose and valine, as shown in Figure 1. The table also includes a visualization of the comparison against the distribution taken from the reference database for each compound. This enables the direct detection of atypical concentrations.

Quantification result table of a honey sample

Verification models were used for non-targeted analysis by comparing the whole NMR profile of a specific sample with the corresponding group reference spectra database. All spectral data points are taken into account irrespective of whether the signals are caused by previously identified molecules or not, resulting in a NMR profile such as the one shown in Figure 2.

Example spectrum showing honey sample adulterated with rice-syrup

Figure 1 shows representative chromatograms of all nine sulfonamides investigated at 0.1 ppb in honey with peak-to-peak (PP) S/N ratio. The S/N ratio for all nine sulfonamides in honey matrix at 0.1 ppb was well above 10, while Figure 2 clearly shows the blank honey matrix contained none of the targeted sulfonamides.

The origin of production plays a crucial role in the analysis of the authenticity of honey samples. Figure 3 shows the validation of the geographical origin of a polyfloral honey from Central America. By incorporating extensive databases it is possible for NMR based screening solutions to incorporate stringent validation conditions including participation in ringtests.

Validation of the geographical origin of a polyfloral honey from Central America

By simultaneously combining targeted and non-targeted analysis, NMR based screening of honey provides the complete solution for quality control and the detection of frauds, such as added syrups or sugar solutions, including unexpected and even unknown frauds. This makes the technique particularly cost efficient as it reduces the number of samples required and increases laboratory throughput. NMR therefore provides the ideal screening solution for quality control and government regulatory laboratories, by delivering a reliable, push button solution that even non-experts can use to accurately determine quality and authenticity of honey.

[1] Codex Alimentarius. 2001. Revised codex standard for honey (No. CODEX STAN 12-1981, Rev 1 (1987), Rev. 2 (2001)).