Isotope Ratio Mass Spectrometry Coupled to Element Analyzer and Liquid Chromatography to Identify Commercial Honeys of Various Botanical Types

Enabling honey quality and authenticity with NMR and LC-IRMS based platform

Honey has been known for economically motivated adulteration around the world, because of its high demand and short supply. As consequence increasing honey production using the deliberate addition of sugar syrups while claiming a fictitious origin and diversifying it to increase its value. Generally, honey testing is supervised by a set of guidelines and quality parameters to ensure its quality and authenticity. As per the many regulatory bodies, current honey scams have been challenging to identify with conventional methods, so quality control labs require sophisticated technology. With these paradigm shifts, the aim of the present review is focused on the authenticity of honey through two important cutting-edge methods viz LC-IRMS and NMR. The LC-IRMS aids in the detection of added C₃ and C₄ sugars. Whereas NMR has provided a potent solution by allowing the classification of botanical varieties and geographical origin along with the quantification of a set of quality parameters in a single experiment.

A review of recent compound-specific isotope analysis studies applied to food authentication

Compound-specific stable isotope analysis (CSIA) of food products is a relatively new and novel technique used to authenticate food and detect adulteration. This paper provides a review of recent on-line and off-line CSIA applications of plant and animal origin foods, essential oils and plant extracts. Different food discrimination techniques, applications, scope, and recent studies are discussed. CSIA δ13C values are widely used to verify geographical origin, organic production, and adulteration. The δ15N values of individual amino acids and nitrate fertilizers have proven effective to authenticate organic foods, while δ2H and δ18O values are useful to link food products with local precipitation for geographical origin verification. Most CSIA techniques focus on fatty acids, amino acids, monosaccharides, disaccharides, organic acids, and volatile compounds enabling more selective and detailed origin and authentication information than bulk isotope analyses.. In conclusion, CSIA has a stronger analytical advantage for the authentication of food compared to bulk stable isotope analysis, especially for honey, beverages, essential oils, and processed foods.

Results of an interlaboratory comparison of a liquid chromatography-isotope ratio mass spectrometry method for the determination of 13C/12C ratios of saccharides in honey

Background

Stable carbon isotope analysis of sugars in honey by LC–isotope ratio mass spectrometry (IRMS) is a useful tool for detecting adulteration of honey with extraneous sugar. Purity criteria based on ¹³C/¹²C ratios of saccharides in honey, determined by LC–IRMS of a large number of authentic honey samples, have been elaborated. However, no interlaboratory comparison (ILC) has yet been performed to estimate the precision of the method under reproducibility conditions.

Objective

To address this knowledge gap an ILC involving 14 laboratories and using six honey samples was conducted.

Methods

The participants were allowed to use their LC–IRMS-based method of choice for sample preparation and compound separation.

Results

The precision figures were estimated according to ISO 5725:1994. The repeatability relative standard deviation (RSD_r) for the determination of δ¹³C values of fructose and glucose varied between 0.3 and 0.5%, with 0.3 and 1.0% for disaccharides, and 0.7 and 2.8% for trisaccharides. The RSD_R varied between 0.8 and 1.8% for the monosaccharides, 1.0 and 1.5% for disaccharides, and 1.4 and 2.8% for trisaccharides.

Conclusion

Based on the obtained precision data the LC–IRMS method for the determination of ¹³C/¹²C ratios of saccharides in honey was considered fit for the conformity assessment of honey with established purity criteria.

Highlights

Precision estimates for a LC–IRMS method to determine ¹³C/¹²C ratios of saccharides in honey were obtained through an ILC. The data created can form the basis for the standardization of the method by interested standards-developing organizations for use in official control.

Evaluation of honey authenticity in Lebanon by analysis of carbon stable isotope ratio using elemental analyzer and liquid chromatography coupled to isotope ratio mass spectrometry

Honey is one of the most valuable sweeteners consumed by humans all over the world. Consequently, it is often a target for adulteration through the addition of different sugar syrups during or after honey production, resulting in a reduction in its nutritive value. For the first time, this study analyzes honey samples of various botanical species collected from different Lebanese regions using element analyzer (EA) and liquid chromatography (LC) coupled with isotope ratio mass spectrometry (IRMS). The δ13 C of bulk honey, its protein fraction, and the main individual sugars (glucose, fructose, disaccharides, and trisaccharide) were determined, in order to characterize and evaluate the authenticity of honey consumed in Lebanon. The results showed that the δ13 C values for bulk honey and its protein range from -26.5‰ to -24.5‰ and from -26.4‰ to -24.7‰, respectively, for authentic samples. δ13 C values for samples adulterated with sugar syrups range from -11.2‰ to -25.1‰ for bulk honey and from -26.6‰ to -23.7‰ for its proteins, with a difference between bulk and protein values between -1 and -8.7‰. Using LC-C-IRMS techniques, the δ13 C of individual sugars provides additional information on the presence of undeclared sugars. We found that all authentic samples had Δδ13 Cf-g and Δδ13 C max values within the naturally occurring range of ±1‰ and ±2.1‰, respectively, while the adulterated samples fall outside the Δδ13 C ranges. The oligosaccharide peak was detected in most adulterated samples.

Carbon isotope ratio of organic acids in sake and wine by solid-phase extraction combined with LC/IRMS

We developed an analytical procedure for determining the δ¹³C values of organic acids in sake and wine using solid-phase extraction combined with liquid chromatography/isotope ratio mass spectrometry (LC/IRMS). First, the solid-phase extraction (SPE) procedure was performed and various tests were conducted to extract organic acids from alcoholic beverages using the simulated sake sample. Under the optimal SPE procedure, high recovery rates (96-118%) and good accuracies (≤ 0.7‰) were thus achieved for the simulated sake and wine samples. Next, we determined the δ¹³C of organic acid (tartaric acid, malic acid, lactic acid, succinic acid) in 9 sake and 11 wine samples. Finally, the δ¹³C values of lactic acid in nine sake samples suggested that lactic acid had been added during the brewing process. The high correlation between the δ¹³C values of tartaric acid and malic acid in 11 wine samples was consistent with their common source, grapes. This analytical method may help to identify when organic acids have been added to sake and wine and to elucidate the process of organic acid production therein. Graphical abstract.

Vibrational Spectroscopy Coupled to a Multivariate Analysis Tiered Approach for Argentinean Honey Provenance Confirmation

In the present work, the provenance discrimination of Argentinian honeys was used as case study to compare the capabilities of three spectroscopic techniques as fast screening platforms for honey authentication purposes. Multifloral honeys were collected among three main honey-producing regions of Argentina over four harvesting seasons. Each sample was fingerprinted by FT-MIR, NIR and FT-Raman spectroscopy. The spectroscopic platforms were compared on the basis of the classification performance achieved under a supervised chemometric approach. Furthermore, low- mid- and high-level data fusion were attempted in order to enhance the classification results. Finally, the best-performing solution underwent to SIMCA modelling with the purpose of reproducing a food authentication scenario. All the developed classification models underwent to a "year-by-year" validation strategy, enabling a sound assessment of their long-term robustness and excluding any issue of model overfitting. Excellent classification scores were achieved by all the technologies and nearly perfect classification was provided by FT-MIR. All the data fusion strategies provided satisfying outcomes, with the mid- and high-level approaches outperforming the low-level data fusion. However, no significant advantage over the FT-MIR alone was obtained. SIMCA modelling of FT-MIR data produced highly sensitive and specific models and an overall prediction ability improvement was achieved when more harvesting seasons were used for the model calibration (86.7% sensitivity and 91.1% specificity). The results obtained in the present work suggested the major potential of FT-MIR for fingerprinting-based honey authentication and demonstrated that accuracy levels that may be commercially useful can be reached. On the other hand, the combination of multiple vibrational spectroscopic fingerprints represents a choice that should be carefully evaluated from a cost/benefit standpoint within the industrial context.

Compound Specific Carbon Isotope Analysis in Sake by LC/IRMS and Brewers' Alcohol Proportion

Sake is a traditional Japanese alcohol. Nowadays, the consumption for Sake is increasing in worldwide and its popularity is growing. However, there are act of fraudulence by additional brewers’ alcohol and sugar. Therefore, a method is needed to find illegal fraud on label. In this work, we analyzed the δ¹³C values of the ethanol (δ¹³C_eth) and glucose (δ¹³C_glu) in Sake by liquid chromatography combined with isotope ratio mass spectrometry for the first time. Further, we developed the criteria using δ¹³C_eth and δ¹³C_glu to check brewers’ alcohol and sugar. In addition, there are some sake categories (Ginjyo and Futsu-shu) allowed to additional brewers’ alcohol up to legally determined percentage. The experimental additions of brewers’ alcohol from a C4 plant were conducted to Junmai, as sake by C3 plants. There was a strong correlation (R = 0.98, P < 0.05) between the percentage of added brewers’ alcohol and the δ¹³C values. We developed the method using the relationship for calculating percentage of brewers’ alcohol for the first time and estimated the percentage for commercial sake. Further, the price of sake was found to be inversely related to the percentage of brewers’ alcohol in the sake.

Heart-cutting two-dimensional liquid chromatography combined with isotope ratio mass spectrometry for the determination of stable carbon isotope ratios of gluconic acid in honey

Liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) is used to analyze various types of samples, including foodstuffs, to determine their authenticity and trace their origin on the basis of their stable carbon isotope ratios (δ¹³C). However, multicomponent samples are difficult to analyze. For example, determining the δ¹³C values of the organic acids in honey is complicated by the presence of large amounts of carbohydrates. Herein, we present a heart-cutting two-dimensional LC/IRMS method for analysis of honey samples. In this method, the organic acids in the samples were first separated from the carbohydrates by a size-exclusion column, and then the organic acids were separated from each other by a reverse-phase column connected to the first column via a switching valve. By means of this method, the δ¹³C values for three organic acids in high-carbohydrate-content simulated honey samples could be determined with high accuracy and precision (≤0.3‰ and ≤0.1‰, respectively). In addition, the gluconic acid δ¹³C values for 25 honey samples were determined with high precision and found to range from -31.7 to -28.5‰ (mean: -30.0 ± 0.7‰). These values shed some light on the mechanism of gluconic acid production. Taken together, our results suggest that this two-dimensional LC method has the potential to be more effective than one-dimensional LC for use in isotopic research.

Stable carbon isotope ratios for organic acids in commercial honey samples

Stable carbon isotope ratios (δ¹³C) for glucose, fructose, disaccharides, trisaccharides, and organic acids in 116 commercial honey samples were measured by LC/IRMS. On the basis of EA/IRMS and LC/IRMS authenticity criteria, 39 of the samples were judged to have been adulterated. The δ¹³C values for organic acids from pure honey, reported here for the first time, ranged from -33.6 to -26.5‰. The mean Δδ¹³C (glucose-organic acids) value was +3.7 ± 0.9‰. Glucose and organic acid δ¹³C values were strongly correlated (R = 0.71, P < 0.001). Gluconic acid, the predominant organic acid in honey, has been reported to be produced via decomposition of glucose by bee glucose-oxidase and certain Gluconobacter spp. This fact was confirmed by isotope analysis.

Determination of carbon isotope ratios for honey samples by means of a liquid chromatography/isotope ratio mass spectrometry system coupled with a post-column pump

RATIONALE

Liquid chromatography/isotope ratio mass spectrometry (LC/IRMS) has been used to authenticate and trace products such as honey, wine, and lemon juice, and compounds such as caffeine and pesticides. However, LC/IRMS has several disadvantages, including the high cost of the CO₂ membrane and blocking by solidified sodium persulfate. Here, we developed an improved system for determining carbon isotope ratios using LC/IRMS.

METHODS

The main improvement was the use of a post-column pump. Using the improved system, we determined δ¹³ C values for glucose with high accuracy and precision (0.1‰ and 0.1‰, respectively; n = 3). The glucose, fructose, disaccharide, trisaccharide, and organic acid constituents of honey samples were analyzed using LC/IRMS.

RESULTS

The δ¹³ C values for glucose, fructose, disaccharides, trisaccharides, and organic acids ranged from -27.0 to -24.2‰, -26.8 to -24.0‰, -28.8 to -24.0‰, -27.8 to -22.8‰, and - 30.6 to -27.4‰, respectively. The analysis time was a third to a half of that required for analysis by previously reported methods.

CONCLUSIONS

The column flow rate could be arbitrarily adjusted with the post-column pump. We applied the improved method to 26 commercial honey samples. Our results can be expected to be useful for other researchers who use LC/IRMS.

Authenticity determination of honeys with non-extractable proteins by means of elemental analyzer (EA) and liquid chromatography (LC) coupled to isotope ratio mass spectroscopy (IRMS)

The present work aims to systematically demonstrate the authenticity of honeys with non-extractable proteins for the first time, by means of EA-IRMS and LC-IRMS. Fifty-three pure honeys of various botanical and geographical origins were studied and a criterion on the basis of the stable carbon isotope ratio characterization of total honey and the main sugars was established for pure honeys. Parameters such as δ¹³C values of total honey and the main sugars were well utilized to identify honeys with non-extractable proteins. Thirty-five honeys from which protein could not be extracted were all identified as adulterated with C-4 sugars or C-3 sugars. The use of isotopic compositions and some systematic differences permit the honeys with non-extractable proteins to be reliably identified. The findings obtained in this work could supplement the AOAC 998.12 C-4 sugar method, with regard to honeys from which protein cannot be extracted.