Honey authenticity: the opacity of analytical reports – part 1 defining the problem

M. J. Walker, S. Cowen, K. Gray, P. Hancock & D. T. Burns

Abstract
The composition of honey, a complex natural product, challenges analytical methods attempting to determine its authenticity particularly in the face of sophisticated adulteration. Of the advanced analytical techniques available, only isotope ratio mass spectrometry (IRMS) is generally accepted for its reproducibility and ability to detect certain added sugars, with nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS) being subject to stakeholder differences of opinion. Herein, recent reviews of honey adulteration and the techniques to detect it are summarised in the light of which analytical reports are examined that underpinned a media article in late 2020 alleging foreign sugars in UK retailers’ own brand honeys. The requirement for multiple analytical techniques leads to complex reports from which it is difficult to draw an overarching and unequivocal authenticity opinion. Thus arose two questions. (1) Is it acceptable to report an adverse interpretation without exhibiting all the supporting data? (2) How may a valid overarching authenticity opinion be derived from a large partially conflicting dataset?

Introduction
In November 2020, the Government Chemist, the UK statutory technical appellate function for food control1, was asked to provide an independent secondary expert opinion on the dataset of analytical results underpinning a UK media article. The story carried the headline “Supermarket brands of honey are ‘bulked out with cheap sugar syrups made from rice and corn’”2; similar media stories recur from time to time, e.g3,4,5,6,7,8. The dataset stemmed from the analyses of 13 own-brand honey samples of major UK retailers, commissioned by a South American bee-keeping organisation. The UK Foods Standards Agency, FSA, supplied three certificates of analysis (CoA), representative of the dataset9. Herein is presented the Government Chemist’s opinion.

A European Directive (‘EU Directive’)10 defines honey as ‘the natural sweet substance produced by Apis mellifera bees from the nectar of plants or from secretions of living parts of plants or excretions of plant-sucking insects on the living parts of plants, which the bees collect, transform by combining with specific substances of their own, deposit, dehydrate, store and leave in honeycombs to ripen and mature’. The Codex Alimentarius definition11 is similar, substituting ‘honey bees’ for the specific species as, worldwide honey may be collected from other honeybee species. The EU Directive was implemented in each of the then member states12. UK Ministerial policy responsibilities on honey are with the UK Department for Environment, Food & Rural Affairs13,14, while general food law enforcement policy is with the FSA15.

Nectar is composed primarily of water, sugars, such as fructose, glucose, and other oligo- and polysaccharides, and minor constituents, such as pollen, proteins, amino acids, aliphatic acid salts, lipids, and flavouring components. Bees process the collected material with enzymes, including diastase (amylase) and invertase (α-glucosidase). Thus, honey is primarily a concentrated aqueous solution of ‘invert’ sugar (the monosaccharides glucose and fructose)16 and typically contains a wide range of saccharides, amino acids, proteins, organic acids, vitamins, minerals, enzymes, polyphenols and pollen. Some of these arise from honey maturation, others from the bees and some from the plants17. Honey composition depends on many factors including the botanical source, geographical origin, species of bee, year and season18. Codex and the EU Directive set certain compositional criteria. The EU Directive differentiates blossom honey (nectar honey in Codex) and honeydew honey, the latter from plant and insect secretions. Honeydew honey is also a concentrated aqueous solution of ‘invert’ sugar, albeit lower in fructose and glucose and typically darker than nectar honey; its chemical characteristics, such as pH, acidity, electric conductivity and other minor components including oligosaccharides are typically higher than in nectar honey19. Codex, the EU Directive, and national law stipulate various labelling options and requirements for honey in addition to general food labelling requirements to protect its authenticity20…

Adulteration of honey and its detection
Anklam (1998)17 reviewed honey authenticity methods finding no single parameter provided unequivocal information about botanical or geographical origins. Some potentially suitable methods were identified indicating a botanical origin from flavonoids, pollen, aroma and marker compounds, although deliberate addition of readily-available known markers and the loss of volatile markers on storage may vitiate detection. It was suggested profiles of oligosaccharides, amino acids and trace elements could be used to verify the claimed geographical origin. A combination of methods with statistical data evaluation was a promising approach. Anklam also noted carbon stable isotope ratio analysis can detect honey adulterated with C4 sugars such as corn syrups or cane sugar (LoD 7%), particularly using the carbon isotope ratio of the honey protein fraction as an internal standard, but the addition of C3 sugars such as beet could not be proved since nectar generally arises from C3 plants. Of the 131 studies reviewed by Anklam, honey sample numbers tended to be small, generally below 30, with several up to 50 and only three between 90 and 100.

Types of adulteration
After Anklam17 subsequent reviews, with variable coverage of the literature (Fig. 1) have expanded on types of adulteration (Fig. 2). The decline of bee populations has also been mentioned21 as a driver.

Read the rest of the article here: https://www.nature.com/articles/s41538-022-00126-6