EFFECT OF PROCESSING METHODS ON THE CHEMICAL COMPOSITION HYPOGLYCEMIC AND HYPOLIPIDEMIC POTENTIALS OF VERNONIA AMYGDALINA

ABSTRACT

Vernonia amygdalina (VA) and Gongronema latifolium (GL) vegetables were processed using four methods; boiling for 5, 10, 15, 20, 25, 30 min, boiling for 5min each in a palm oil and salt (NaCl) medium, moist heating at 40 oC, 60 oC, 80 oC and 100 oC for 5 min, drying under the heat of the sun (35 oC – 40 oC), solar (45 oC – 50 oC ) and oven (50 oC – 55 oC) and de-bittered by boiling and squeeze-washing. Effects of these processing methods on the chemical composition, hypoglycemic and hypolipidemic potentials of the vegetables were evaluated. In vitro antioxidant potentials of processed and unprocessed vegetables were estimated using the 1,1-Diphenyl-2-picryl hydrazyl radical (DPPH) while superoxide dismutase and glutathione peroxidase were used for in vivo model. The hypoglycemic properties of aqueous extracts of VA and GL were evaluated in rats using a dosage of 300g/Kg bodyweight. The effect of the vegetable extracts on rats lipid peroxidation and liver

function tests were studied. Boiling process reduced (p<0.05) all the nutrients excluding crude fat, carbohydrate and mineral contents. Phytochemical content of both vegetables were similar.However unprocessed VA had higher (p<0.05) alkaloid (1.73g/100g), tannin (0.23g/100g), saponin (8.02 g/100g) and phytate (1.46g/100g) values than unprocessed GL but flavonoids and anthocyanin were significantly (p<0.05) higher in GL. Boiling in a medium containing palm oil and salt (NaCl) reduced the saponin content of both vegetables suggesting that oil and salt form complex compounds with Saponin reducing its concentration. Similar trends were obtained for the vitamin contents of both vegetables.

Boiling and drying processing methods reduced (p<0.05) vitamin C while squeezed-washing reduced (p<0.05) vitamins A, C, and E in both vegetables. Administration of 300g/kg body weight of aqueous extract of VA vegetables for 13days reduced blood sugar level of diabetic rats with a peak blood glucose level of 555mg/ml reduced to 162mg/ml (40.5% reduction compared to the control). Aqueous extracts of VA controlled sugar level of diabetic rats (320.40 – 162.20mg/ml) and GL (372 – 158mg/ml) for 13days post treatment. The VA and GL extracts showed potential protective abilities on the rats liver using liver enzyme indication tests (ALP, ALT and AST). Processing by boiling for 5min reduced (p<0.05) the anti- nutrients saponin and phytate but did not adversely affect the antioxidant, hypoglycemic and hypolipidemic properties of these vegetables and was consequently considered to be the best processing method with optimal potentials.