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.