Medicinal Plants Classification Biosynthesis and ... - Index of

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Vandana Gulati, Ian H. Harding and Enzo A. Palombo
in the food extract enzyme-inhibition mechanism. The results from these experiments showed
that common vegetables and spices contained significant antidiabetic activity in vitro, as well
as anti-ACE activity, and suggested that dietary modification to include these types of foods
along with balancing carbohydrate intake throughout the day may represent a promising
strategy to help control postprandial hyperglycemia through modulation of carbohydrate
absorption. Dietary α-amylase and α-glucosidase inhibitors from common foods are
potentially safer, therefore, may be a preferred alternative for the reduction of carbohydrate
absorption and control of blood glucose (24).
The inhibitory effects of polyphenol components of berries on various digestive enzymes
were studied and it was found that anthocyanins inhibit α-glucosidase and reduce blood
glucose levels after ingestion of meals rich in starch, and they may therefore control
hyperglycemia. Ellagitannins, which are present in berries, inhibit α-amylase activity.
Raspberries and strawberries contain high amounts of ellagitannins and anthocyanins. Berry
polyphenols like flavonols, anthocyanidins, ellagitannins and proanthocyanidins can inhibit
protease enzyme which could, in turn, affect protein digestion in the gastrointestinal tract.
Proanthocyanidins can inhibit gastrointestinal lipase activity which helps in the control of
obesity by reducing fat digestion. Polyphenol components in berries, fruits and other
vegetables provide health benefits by inhibition of these digestive enzymes thus providing an
alternative to pharmaceutical and nutraceutical treatment for non-insulin dependent diabetes
and obesity (25).
The National Diabetes Education Program of the National Institutes of Health (NIH)
recommends that eggplant should be included in the diet for the management of Type II
diabetes. The phenolic-enriched antioxidant activity and α-glucosidase inhibitory potential
might help to reduce hyperglycemia-induced pathogenesis. This was tested experimentally in
vitro by extracting four varieties (Purple, White, Graffiti, Italian) of fresh and well-ripened
eggplant (Solanum melongena), with water and screened for activity using α-amylase, αglucosidase
and ACE-I inhibition, DPPH and total phenolic assays. The results indicated that
phenolic-enriched extracts had high α-glucosidase inhibitory activity, moderate antioxidant
activity and moderate to high ACE-I inhibitory activity. Eggplant may therefore control
glucose absorption and decrease the risk of related hypertension because of its high fibre,
phenolic compounds and low soluble carbohydrate content. Inhibition of these enzymes
provide strong biochemical basis for management of Type II diabetes by controlling glucose
absorption and associated hypertension. The phenolic antioxidant-enriched dietary strategy
also has the potential to reduce cellular oxidation stress which is also related to diabetes (26).
In an in vitro epididymal fat cell assay, tea has been shown to increase insulin activity.
Black, green, oolong and herbal teas all increased insulin activity and the insulin potentiating
activity of green and oolong teas was considered to be due to epigallocatechin gallate. The
other compounds responsible for enhancing insulin activities are epicatechin gallate, tannins
and theaflavins (27). These data were supported by in vitro enzyme inhibition analysis of
other phenolic phytochemicals including the four types of tea (green tea, oolong tea, black tea
and white tea) and several varieties of red and white wine. The aqueous extract of black tea
showed the highest α-glucosidase inhibition followed by white and oolong tea. Red wines
had high α-glucosidase inhibition compared to white wine and the inhibitory activity was
correlated to phenolic content, antioxidant activity and phenolic profile of the extracts. These