DETERMINATION OF ANTIOXIDANT ACTIVITY AND TOTAL PHENOLICS OF SELECTED THAI HONEYS

The aim of this research was to determine the bioactive properties of seven floral honeys originated in Thailand including sesame (Sesamum indicum L.), lychee ( Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.), sunflower (Helianthus annuus), korlan (Nephelium hypuleucum Korz.), sabsue (Eupatorium odoratum L.) and plaunoi (Croton stellatopilosus Ohba). Results indicated that reducing sugar content ranged from 66.5 to 73.0%. Total phenolic content ranged from 58.7 to 165.2 mg GAE/100 g, flavonoid content varied between 4.8 to 27.5 mg QE/100 g. Three different methods were used to evaluate the antioxidant activity; the 2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity (DPPH) assay, the 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assay and the ferric reducing/antioxidant power (FRAP) assay. Inhibition concentration at 5 0% (IC50) by DPPH assay and ABTS assay were found in the range from 0.02 to 0.12 g/ml and from 0.25 to 1.03 g/ml, respectively and the ferric reducing antioxidant power (FRAP) assay was found in the range from 1 4 7.5 – 550.0 μmol Fe (II)/100 g of honey. Antioxidant capacity of honey was positively correlated between the total phenolics and flavonoid contents. Introduction: Botanical diversity and availability throughout the year has made Thailand a growing potential for honey production and export. The phytochemical constituents of a honey are known to be associated with their origin and in turn the quality of the honey. Honey is a supersaturated solution of sugars which has been consumed for its high nutritive value and its association in human health. The composition of honey depends on the plant species that honeybees visited as well as the environmental, processing and storage conditions. The use of honey in therapeutical treatment and prevention of numerous diseases resulted from oxidative damages is due to its antioxidant capacity. Phenolic compounds acting as minor constituents demonstrate antioxidant properties including phenolic acids and flavonoids of which its antioxidant activity varies greatly depending on the honey floral source. However, there is a lack of information on the comparative biochemical properties of Thai honeys from various floral sources. Therefore, the objective of this study was to investigate the antioxidant properties of Thai honeys as to establish values for consumers. Methodology: Materials: Seven honey samples of known floral origin; lychee (Litchi chinensis Sonn.) (A), longan (Dimocarpus longan Lour.) (B), korlan (Nephelium hypoleucum Kurz.) (C), sunflower (Helianthus annuus) (D), plaunoi (Corton stellatopilosus Ohba.) (E), sesame (Sesamum indicum L.) (F), and sabsue (Eupatorium odoratum L.) (G) were obtained directly from beekeepers farms of two provinces in the Northern part of Thailand and maintained at cool temperature (20°C± 5) in their closed bottles prior to analysis. All the samples were informed of being freshly harvested and manufactured with less than 3 months olds by the manufacturers. The chemicals used in determination of antioxidant capacity were all analytical grade. Determination of reducing sugar: All honeys were analyzed in triplicates according to the method proposed by the International Honey Commission and in agreement with the Codex Alimentarius.