Authentication of Iranian honey samples: Physicochemical parameters investigation along with the electrochemical measurement of gallic acid by g-C3N4/AuNPs modified carbon paste electrode

Abstract

Introduction: Honey is a natural food with therapeutic and health benefits for humans. Interest in honey authentication has increased in relation to botanical and geographical origin and fraud [1]. Phenolic compounds are formed in the plants nectar to attract pollinating insects and found in honey owing the nectar processing by bees. Polyphenol gallic acid (GA) is used as a chemical marker in food analytical researches [2,3]. Experimental / Methods: Here, to investigate the honey authentication, some physicochemical parameters of Iranian honey samples (thyme, astragalus, coriander, barberries, eucalyptus and ziziphus) such as pH, diastase activity, sucrose, proline and hydroxymethyl furfural (HMF) contents were measured according to Iran national standards organization (INSO 92). Also, the modified carbon paste electrode with synthesized g-C3N4/AuNPs nanocomposite (g-C3N4/AuNPs/CPE) was used to GA determination in honey samples by differential pulse voltammetry technique (DPV) based on GA oxidation peak at 0.5 V. Results and discussion: Sucrose content in honey samples was ranged 0.97 to 7.70 g/100 g. According to the codex committee on sugars (CCS), just this parameter in ziziphus honey (7.70 g/100 g) exceeded 5 g/100 g, due to its higher content in ziziphus flower nectar. Acidic pH was obtained for all honey samples; however the pH 6.25 for ziziphus honey exceeded the standard range (3.40-6.10), because of fermentation occurrence. All samples were situated at the standard proline content (≤180 mg/Kg). The highest and lowest proline contents were obtained for thyme and barberry honey samples; 843.0 and 340.0 mg/Kg, respectively. The diastase activity and HMF were used to determine the freshness and overheating of honey that registered in all samples 9.10-17.08 DN (standard: ≤8 DN) and 0.67-26.30 mg/Kg (standard: ≥ 40 mg/Kg). The GA content in thyme, barberry, astragalus, eucalyptus, and coriander honeys were 0.016, 0.015, 0.014, 0.006 and 0.004 mg/g, respectively and there was no oxidation peak for GA in ziziphus honey. Conclusion: Honey authentication has complexity and very different depending on the time of harvest, packaging, botanical origin, storage time, and degree of heat treatment. Here, g-C3N4/AuNPs/CPE was successfully used to GA identification in honey samples and accordingly recommends to qualification and prevent honey frauds.