EFFECT OF THERMAL TREATMENT ON BIOCHEMICAL COMPOSITION AND ANTIOXIDANT ACTIVITIES OF HONEY COLLECTED FROM SOUTH ETHIOPIA: THE CASE OF WOLAYITA ZONE

<strong>ABSTRACT</strong>: Honey is a natural sweet substance produced by honey bees from the nectar of blossoms or from the secretion of living parts of plants. Honey is renowned for its antioxidant and medicinal properties. It is typically heated and filtered during processing to avoid crystallization. In the present study we investigate the effect of thermal treatment at 650C and 950C for 30 min on biochemical composition and antioxidant activity of three honey varieties. Yellow multi floral (YMF), light brown multi floral (LBMF), and dark brown multi floral (DBMF) honeys. Total sugar, reducing sugar and sucrose contents were determined by Lane and Enyon method. The free acidity value was quantified by standard titration method. Folin Ciocalteu, aluminum chloride, standardized Iodine solution and vanillin-HCl were used to determine the total phenolic (TPC), total flavonoid (TFC), vitamin C content, and tannin contents, respectively. Antioxidant capacity of honey was determined using 1, 1-Diphenyl-2 Picryl-Hydrazyl (DPPH) scavenging assay, phosphomolybdenum and ferric reducing power assay. The YMF honey sample contained the highest total reducing sugar (72.59 ± 1.93 g/100g of honey), DBMF honey sample contained the highest total sugar content (75.43 ± 6.29 g/100g of honey) and LBMF honey sample had the highest sucrose content (4.55 ± 1.10 g/100g of honey). Similarly, YMF honey sample contained the highest free acidity value (57.50 ± 6.36 milli-equivalents per kilogram of honey) after heating at 950C for 30 min. Unheated DBMF honey sample had the highest TPC (111.95 ± 0.81 milligram of gallic acid equivalent per 100 gram of honey) and TFC (93.79 ± 15.66 mg milligram of catechin equivalent per 100 gram of honey). Before heat treatment LBMF honey sample contained the highest vitamin C content (18.05 ± 1.84 mg/100g of honey) and the highest total condensed tannin was obtained in DBMF honey sample (0.40 ± 0.07 milligram of catechin equivalent per gram of honey). Unheated LBMF honey showed stronger antioxidant capacity, (IC50 = 6.1 ± 0.67 mg/mL) and (51.96 ± 0.37 milligram of butylated hydroxytoluene equivalent per 100 gram of honey) as determined by the DPPH (EC50) and total antioxidant activity, respectively. Whereas, unheated DBMF honey showed, the strongest reducing power (100.71 ± 1.23 milligram ascorbic acid equivalents per 100 gram of honey). Based on present investigation, it could be concluded that a reduction in total phenolic content, flavonoid content, vitamin C, tannin content and antioxidant activities of the honey samples were observed during thermal treatment at 65 and 950C for 30 min, while free acidity increased. All reactions were greatly higher before this treatment, thus the heating applied determine certain changes on the level of the parameters of quality of these honey samples. TPC and TFC of honey samples heated at different temperatures were strongly correlated with the DPPH scavenging activity (%), moderately correlated with ferric reducing power but weakly correlated with the total antioxidant activity. Due to the presence of phenolic compounds and established antioxidant activity, the studied honey samples could be selected for processing extracts with health-promoting properties or to be incorporated into functional foods or products with bio active properties related to oxidative stress mediated human disorders.