Structural and functional properties of bioactive vegetable leaf polyphenols
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Polyphenols of natural sources especially from plants have increasingly become important due to their ability to bind enzyme proteins, inhibit free radicals and reduce carbohydrate and lipid digestion. Polyphenols have received a lot of interest because they are important alternatives to drugs with potential health benefits. Therefore, the aim of this thesis was to determine the antioxidant, antihypertensive and digestive enzymes inhibitory properties of water-soluble polyphenols of Amaranthus viridis (AV), Solanum macrocarpon (SM), and Telfairia occidentalis (TO) leaves. The leaf polyphenols were extracted using double distilled water for 4 h at 60oC and then freeze dried to yield AV, SM and TO extracts. The three vegetable extracts had strong antioxidant properties, which were measured as ability to scavenge free radicals and chelate metal ions. During a 24-h test, AV, SM and TO extracts reduced systolic blood pressure (SBP) of spontaneously hypertensive rats (SHR) after oral administration of 100 mg/body weight (BW) better than the 500 mg/kg BW dose. All the three vegetable extracts (AV, SM and TO) also inhibited in vitro activities of digestive enzymes (pancreatic lipase, α-amylase, α-glucosidase, chymotrypsin, and trypsin). Results indicate that TO extracts were better inhibitors of the digestive enzymes followed by SM and AV extracts, except for trypsin. The mode of inhibition was identified to be competitive for trypsin, α-amylase, α-glucosidase, chymotrypsin α-amylase, α-glucosidase, chymotrypsin. The TO extract was the most bioactive and was further fractionated into chlorophyll and non-chlorophyll fractions, which were then studied for their antioxidant and enzyme inhibition properties.