Comparison of Differences of α-Dicarbonyl Compounds between Naturally Matured and Artificially Heated Acacia Honey: Their Application to Determine Honey Quality

Novel insight into Amadori compounds: Fate of Amadori compounds in food supply chain

Amadori compounds, pivotal intermediates in the Maillard reaction, act as flavor enhancer, browning precursor, and functional component. Amadori compounds consisting of diverse amino and carbonyl groups might show distinct flavor attributes and functional activities. Food production involves many supply chain stages where thermal treatment might produce Amadori compounds, and processing techniques and circumstances might affect the generation and stability of Amadori compounds. Moreover, gastrointestinal digestion might also influence the stability of Amadori compounds. To date, there is a lack of comprehensive review on the impact of various supply chain stages and digestion on Amadori compounds. This paper reviewed all reported Amadori compounds derived from diverse reducing sugars (glucose, xylose, ribose, maltose) and amino-containing compounds (common and specific amino acids, peptides), and compared differences in synthetic efficiency, flavor property, and functional activity among them; aggregated qualitative techniques; encapsulated quantitative techniques including indirect quantification and direct quantification, and intuitively compared strengths and weaknesses of these techniques; and outlined influence of processing, cooking, storage, and digestion on formation and stability of Amadori compounds. Appropriate processing techniques and conditions favored the generation and stability of Amadori compounds. Baking, frying, and roasting greatly facilitated Amadori compounds accumulation compared to steaming and boiling. Prolonged cooking at relatively low temperature favored Amadori compounds accumulation, whereas high-temperature cooking for a short duration resulted in fewer accumulation. Amadori compounds showed greater digestion resistance and could be absorbed by the intestine. This review offers scientific instruction for producing high-quality products with abundant Amadori compounds, or extracting plentiful Amadori compounds from processed foods as versatile food additives.

Exploring the Formation of Chemical Markers in Chaste Honey by Comparative Metabolomics: From Nectar to Mature Honey

Identification of chemical markers is important to ensure the authenticity of monofloral honey; however, the formation of chemical markers in honey has received little attention. Herein, using comparative metabolomics, we first identified chemical markers in chaste honey and then explored their formation and accumulation from nectar to mature honey. We identified agnuside and p-hydroxybenzoic acid glucosides as chemical markers for chaste honey. Besides, we developed an UHPLC-MS/MS method for quantifying these markers and found that their levels varied significantly across sample sources. We compared the presence of these compounds in chaste nectar and mature honey. The outcomes underscore that these characteristic compounds are not simply delivered from nectar to mature honey, and activities of honeybees (collecting and processing) play a pivotal role in their formation and accumulation. These observations shed light on how mature honey can form its unique qualities with a rich assortment of natural bioactive compounds, potentially supporting health benefits.

Investigations of Major α-Dicarbonyl Content in U.S. Honey of Different Geographical Origins

α-Dicarbonyls are significant degradation products resulting from the Maillard reaction during food processing. Their presence in foods can indicate the extent of heat exposure, processing treatments, and storage conditions. Moreover, they may be useful in providing insights into the potential antibacterial and antioxidant activity of U.S. honey. Despite their importance, the occurrence of α-dicarbonyls in honey produced in the United States has not been extensively studied. This study aims to assess the concentrations of α-dicarbonyls in honey samples from different regions across the United States. The identification and quantification of α-dicarbonyls were conducted using reverse-phase liquid chromatography after derivatization with o-phenylenediamine (OPD) and detected using ultraviolet (UV) and mass spectrometry methods. This study investigated the effects of pH, color, and derivatization reagent on the presence of α-dicarbonyls in honey. The quantification method was validated by estimating the linearity, precision, recovery, method limit of detection, and quantification using known standards for GO, MGO, and 3-DG, respectively. Three major OPD-derivatized α-dicarbonyls including methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), were quantified in all the honey samples. 3-Deoxyglucosone (3-DG) was identified as the predominant α-dicarbonyl in all the U.S. honey samples, with concentrations ranging from 10.80 to 50.24 mg/kg. The total α-dicarbonyl content ranged from 16.81 to 55.74 mg/kg, with the highest concentration measured for Southern California honey. Our results showed no significant correlation between the total α-dicarbonyl content and the measured pH solutions. Similarly, we found that lower amounts of the OPD reagent are optimal for efficient derivatization of MGO, GO, and 3-DG in honey. Our results also indicated that darker types of honey may contain higher α-dicarbonyl content compared with lighter ones. The method validation results yielded excellent recovery rates for 3-DG (82.5%), MGO (75.8%), and GO (67.0%). The method demonstrated high linearity with a limit of detection (LOD) and limit of quantitation (LOQ) ranging from 0.0015 to 0.002 mg/kg and 0.005 to 0.008 mg/kg, respectively. Our results provide insights into the occurrence and concentrations of α-dicarbonyl compounds in U.S. honey varieties, offering valuable information on their quality and susceptibility to thermal processing effects.

Amadori compounds: analysis, composition in food and potential health beneficial functions

Amadori compounds (ACs) are key intermediates of the Maillard reaction, and found in various thermally processed foods. Simultaneous analysis of multiple ACs is challenging due to the complex amino acid and carbohydrate compositions, and the different food matrices. Most studies focus on the effects of ACs on food flavor and related sensory properties, but not their biological functions. However, increasing evidence shows that ACs possess various beneficial effects on human health, thus a comprehensive review on the various biological activities is warranted. In this review, we summarized the composition and content of ACs in different foods, their formation and degradation reactions, and discussed the latest advances in analytical methods of ACs and their biological functions related to human health. Limitations and research gaps were identified and future perspectives on ACs research were proposed. This review points to the needs of systematic and comprehensive in vitro and in vivo studies on human health related biological functions of ACs and their mechanisms of action, particularly the synergistic effects with other food components and drugs, and roles in intestinal health and metabolic syndrome.

Simultaneous determination of six α-dicarbonyl compounds in traditional Chinese medicines using high-performance liquid chromatography-fluorescence detector with pre-column derivatization

A reliable method for determination of six α-dicarbonyl compounds in traditional Chinese medicines was first developed and validated by high-performance liquid chromatography-fluorescence detector with pre-column derivatization. α-Dicarbonyl compounds in traditional Chinese medicines were extracted and derivatized with 2,3-diaminaphthalene. The derivatization procedure of six α-dicarbonyl compounds was confirmed by high-resolution mass spectrometry. The limits of quantitation for six α-dicarbonyl compounds ranged from 3.70 × 10-3 to 2.21 × 10-2  μM. The established method showed good linearity (regression coefficient > 0.9990), precision (relative standard deviation < 3.37%), and high recovery (97.8%∼113.1%). The developed method was successfully applied to detect the six α-dicarbonyl compounds in traditional Chinese medicines. The result exhibited six α-dicarbonyl compounds was found in the 15 kinds of traditional Chinese medicines, which suggested us that the determination of α-dicarbonyl compounds should be paid more attention in the quality control of traditional Chinese medicines.

Chaste honey in long term-storage: Occurrence and accumulation of Maillard reaction products, and safety assessment

Honey, a natural sweetener that can be stored long-term, is prone to Maillard reactions. Maillard reaction products (MRPs), such as 5-hydroxymethylfurfural (5-HMF), α-dicarbonyl compounds (α-DCs), and advanced glycation end products (AGEs), negatively affect human health. We analyzed MRP accumulation in chaste honey over four years. In the first year, α-DCs were dominant with total contents of 509.7 mg/kg. In the second year, Amadori compounds increased, accounting for the largest percentage. Their formation at the initial stage showed inhibition of the Maillard reaction over time. AGE contents were approximately 1.00 mg/kg over four years, which is negligible compared to other foods. Increased 5-HMF was significantly correlated with storage time (p < 0.01), making it a suitable indicator of honey quality. Due to the lack of MRP risk assessments, we compared our findings with daily intake of MRPs from other foods, and the levels of MRPs in honey over four years are acceptable.

Rapid Characterization of Maillard Reaction Products in Heat-Treated Honey by Nanoelectrospray Ionization Mass Spectrometry

Amadori rearrangement products (ARPs) and α-dicarbonyl compounds (α-DCs) are critical intermediates in the Maillard chemistry. The screening of artificially heated honey (AH) is currently based on chromatography-mass spectrometry, which is commonly accompanied with the longer pretreatment and detection time. Here, low-abundance ARPs were detected directly in high-sugar environment by nanoelectrospray ionization mass spectrometry (nanoESI-MS) coupled with borosilicate glass capillaries (O-tips). When O-tips were replaced by borosilicate theta capillaries (θ-tips), the microdroplets allowed the derivatization of α-DCs to be accomplished on the millisecond timescale, rather than hours in conventional protocols. The results indicated that two ARPs and α-DCs of m/z 235 were significantly up-regulated in AH. Meanwhile, the straightforward differentiation between naturally matured honey (NH) and AH was achieved by nanoESI-MS fingerprints combined with multivariate analysis. The method may provide a rapid characterization of Maillard reaction products (MRPs), which exhibits the great application potential in other complex food matrix.

α-Dicarbonyl compounds in food products: Comprehensively understanding their occurrence, analysis, and control

α-Dicarbonyl compounds (α-DCs) are readily produced during the heating and storage of foods, mainly through the Maillard reaction, caramelization, lipid-peroxidation, and enzymatic reaction. They contribute to both the organoleptic properties (i.e., aroma, taste, and color) and deterioration of foods and are potential indicators of food quality. α-DCs are also important precursors to hazardous substances, such as acrylamide, furan, advanced lipoxidation end products, and advanced glycation end products, which are genotoxic, neurotoxic, and linked to several diseases. Recent studies have indicated that dietary α-DCs can elevate plasma α-DC levels and lead to "dicarbonyl stress." To accurately assess their health risks, quantifying α-DCs in food products is crucial. Considering their low volatility, inability to absorb ultraviolet light, and high reactivity, the analysis of α-DCs in complex food systems is a challenge. In this review, we comprehensively cover the development of scientific approaches, from extraction, enrichment, and derivatization, to sophisticated detection techniques, which are necessary for quantifying α-DCs in different foods. Exposure to α-DCs is inevitable because they exist in most foods. Recently, novel strategies for reducing α-DC levels in foods have become a hot research topic. These strategies include the use of new processing technologies, formula modification, and supplementation with α-DC scavengers (e.g., phenolic compounds). For each strategy, it is important to consider the potential mechanisms underlying the formation and removal of process contaminants. Future studies are needed to develop techniques to control α-DC formation during food processing, and standardized approaches are needed to quantify and compare α-DCs in different foods.

Insight into the Recent Application of Chemometrics in Quality Analysis and Characterization of Bee Honey during Processing and Storage

The application of chemometrics, a widely used science in food studies (and not only food studies) has begun to increase in importance with chemometrics being a very powerful tool in analyzing large numbers of results. In the case of honey, chemometrics is usually used for assessing honey authenticity and quality control, combined with well-established analytical methods. Research related to investigation of the quality changes in honey due to modifications after processing and storage is rare, with a visibly increasing tendency in the last decade (and concentrated on investigating novel methods to preserve the honey quality, such as ultrasound or high-pressure treatment). This review presents the evolution in the last few years in using chemometrics in analyzing honey quality during processing and storage. The advantages of using chemometrics in assessing honey quality during storage and processing are presented, together with the main characteristics of some well-known chemometric methods. Chemometrics prove to be a successful tool to differentiate honey samples based on changes of characteristics during storage and processing.

Identification of Pigmented Substances in Black Honey from Leucosceptrum canum: Novel Quinonoids Contribute to Honey Color

Leucosceptrum canum (Lamiaceae) honey (LCH) is a rare and high-value honey with an unusual dark brown color. Its pigments may be related to the purported health benefits of the honey and could serve as indicators of authentic LCH. Here, we purified the pigmented substances contributing to LCH's color and identified them using high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy. The major pigmented substances were 1-[4-(3-carboxy-propylamino)-3,6-dioxo-cyclohexa-1,4-dienyl]-pyrrolidine-2-carboxylic acid (GPBQ), 1-[4-(3-carboxy-propylamino)-3,6-dioxo-cyclohexa-1,4-dienyl]-pyrrolidine-2-carboxylic acid. (GAPBQ), and 2,5-di-(N-prolyl)-para-benzoquinone (DPBQ). According to UHPLC-DAD data recorded at 370 nm, GPBQ, GAPBQ, and DPBQ contents ranged from 2.58 to 5.13, 2.93 to 4.96, and 4.26 to 9.22 mg/kg, respectively. These amino acid-quinone conjugates, found here for the first time, are pigments that can serve as markers to control the quality of LCH.

Response surface approach to optimize temperature, pH and time on antioxidant properties of wild bush (Plectranthus rugosus) honey from high altitude region (Kashmir Valley) of India

In this study, the combined effect of temperature (60 to 80 °C) time (10 to 15 min.) and pH (3 to 6) was employed on the anti-oxidant potential (1,1-diphenyl-2-picrylhydrazyl-radical scavenging activity-DPPH-RSA, total phenolic content-TPC, and total flavonoid content-TFC) of wild bush Indian honey from high altitudes of Kashmir Valley by using response surface methodology (RSM). The statistical analysis showed that all the process variables had a substantial effect on the responses related to DPPH-RSA, TFC, and TPC, all of which increased as temperature and time increased. With an increase in pH, the antioxidant activity of wild bush honey was significantly decreased. The heat treatment of honey at high temperature (80 °C) was found to be more efficacious than at 70 and 60 °C, respectively. The findings showed that at higher temperature, browning pigments were formed which enhanced considerably the antioxidant activity of honey.

Isotope-Coding Derivatization for Quantitative Profiling of Reactive α-Dicarbonyl Species in Processed Botanicals by Liquid Chromatography-Tandem Mass Spectrometry

α-Dicarbonyls (α-DCs) are key reactive Maillard intermediates with structural diversity and are widely found in foods and in vivo, but little is known regarding the complete molecular profiles of these potentially harmful electrophiles. Herein, we reported a novel isotope-coding derivatization (ICD) strategy for the broad-spectrum, quantitative profiling of (non)target α-DC species in natural foodstuffs. It utilized differential isotope labeling (DIOL) with a reagent pair o-phenylenediamine (OPD)/OPD-d₄ (deuterated) to form stable quinoxalines for class-specific fragmentation-dependent acquisition using liquid chromatography-hybrid quadrupole linear ion trap mass spectrometry (LC-QqLIT). A combination of facile one-pot quantitative labeling and convenient cleanup protocol afforded satisfactory sensitivity, linearity, accuracy (81-116%), and process recovery (86-109% with RSDs < 10%) by matrix-matched ICD-internal standard calibration, without significant matrix interference (-9 to 5%), isotopic effect (<0.5%), and cocktail effect. A more generic DIOL-based LC-QqLIT algorithm integrated double precursor ion and neutral loss scan to trigger enhanced product ions with the unique isobaric doublet tags (4 Da shift), enabling simultaneous screening and relative quantitation of nontarget α-DC analogues in a single analysis. This study has widened the vision on complex α-DC profiles in traditional botanicals, which revealed a wide occurrence of α-DCs in such processed sugar-rich products, yet their abundance varied greatly among different samples.

Identification of the Maillard reaction intermediates as divalent iron complexes in alanine/glucose/FeCl2 model system using ESI/qTOF/MS/MS and isotope labelling technique

Due to their high reactivities and short half-lives, the detection of Maillard reaction intermediates is relatively difficult to achieve in a single analytical run. In this study, the formation of Maillard reaction intermediates from heated alanine/glucose mixtures (110 ​°C for 2 ​h) was investigated through their complexation with divalent iron using electrospray ionization/quadrupole time-of-flight mass spectrometry and isotope labeling techniques. Analysis of the mixtures indicated that this approach allows the simultaneous detection of many important labile and reactive Maillard reaction intermediates along with unreacted alanine and glucose in addition to various other Maillard reaction products, such as glyceraldehyde, erythrose, ribose, acetol, glycolaldehyde, fructosamine, glucosone, osones, deoxyosones, and Amadori products. Some osones and deoxyosones also formed their corresponding Schiff bases with alanine. The above mentioned Maillard reactions intermediates were detected either as binary metal complexes with alanine or with other enediol generating species including self-complexation adducts and they formed positively charged ions such as [M + H]⁺, [M + Na]⁺, [M + K]⁺, [M ​+ ​Fe³⁵Cl]⁺, and [M ​+ ​Fe³⁷Cl]⁺, that can be detected using the positive ionization mode.

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Glucose/alanine Maillard reaction intermediates were identified as iron complexes.

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In this approach ESI/qTOF/MS/MS and isotope labelling techniques were utilized.

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The technique allowed identification of both stable and labile intermediates.

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Amadori compounds and various osones were detected as stable metal complexes.

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MS/MS data of free and complexed ARPs have indicated the stability of the latter.

Detection of acacia honey adulteration with high fructose corn syrup through determination of targeted α‑Dicarbonyl compound using ion mobility-mass spectrometry coupled with UHPLC-MS/MS

High-value acacia honey is often adulterated with inexpensive high fructose corn syrup (HFCS), due to their similar color and sugar composition. α‑Dicarbonyl compounds formed by Maillard reaction or caramelization during heat treatment or storage, differ between HFCS and honey due to differences in starting materials and processing methods. In this study, we compared α-dicarbonyl compounds in acacia honey and HFCS by Ion Mobility-Mass Spectrometry and multivariate statistical analysis. Through α-dicarbonyl compound derivatization with o-phenylenediamine, we screened a marker with 189.1023 m/z and 139.3 Å² Collision Cross-Section that can distinguish HFCS from acacia honey. Nuclear magnetic resonance spectra identified this marker compound as 3,4-dideoxypentosulose. We then used chromatography-coupled tandem mass spectrometry to quantitate 3,4-dideoxypentosulose in market samples of honey and HFCS and found that 3,4-dideoxypentosulose was negligible (<0.098 mg/kg) in honey, but prevalent in HFCS (≧1.174 mg/kg), indicating 3,4-dideoxypentosulose can serve as an alternative indicator of HFCS adulteration of acacia honey.

Profiling of glucose degradation products through complexation with divalent metal ions coupled with ESI/qTOF/MS/MS analysis

Sugar degradation products generated through thermal treatment of foods are considered the key precursors for various flavor compounds, toxicants and browning, but their high reactivity makes their detection difficult. In this study, a convenient analytical procedure for profiling of various reactive sugar intermediates having enediol or α-dicarbonyl moieties through complexation with divalent metal ions combined with electrospray ionization/quadrupole time-of-flight mass spectrometry was developed. Excess divalent iron chloride (FeCl₂) was added to glucose or ¹³U6-[glucose] solutions in methanol either before or after heating at 110 °C for 2 h, and the samples were analyzed by tandem mass spectrometry. The results indicated the formation of ethylene glycol, glycolaldehyde, glyceraldehyde, glycerol, methylglyoxal, glyoxylic acid, erythrose, erythrosone, 3-deoxy-erythrosone, erythritol, ribose, ribosone, 3-deoxy-ribose, ribitol, 3-deoxy-glucosone, and rhamnose. These sugars and sugar degradation products acting as bidentate ligands were detected as positively charged mono- and bis-sugar iron complexes in the form of [M + H]⁺, [M + Na]⁺, [M + K]⁺, [M + Fe³⁵Cl]⁺, and [M + Fe³⁷Cl]⁺, as well as by charge localization on iron [M]⁺. The divalent metal complexation technique was applied for the profiling of sugar degradation products in aged manuka honey.

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Sugar degradation products (SDP) were profiled using FeCl₂ and ESI/qTOF/MS analysis.

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SDPs acted as bidentate ligands and complexed with iron.

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Complexation of SDP with iron allowed development of positive charge for MS analysis.

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Different positively charged metal complexes were identified such as [M]⁺ and [M + H]⁺.