Abstract
A collection of tropical medicinal plants from East Malaysia's rainforests are used by indigenous tribes for their curative properties. Despite their purported healing properties, these forest plant species are largely unexplored and hence remain virtually unknown to the outside world. In this study, antidiabetic properties of Psychotria viridiflora, a plant used to treat diabetes by a local community in Sarawak, Malaysia were investigated. Ethyl acetate (EA) extract of P. viridiflora stem was found to exhibit high starch hydrolase inhibition activity with an IC50 value of 15.4 ± 2.1 μg/ml against porcine α-amylase and an IC50 value of 32.4 ± 3.7 μg/ml against rat intestinal α-glucosidase. A complex mixture of A-type oligomeric proanthocyanidins containing (epi)fisetinidol, (epi)afzelechin, (epi)guibourtinidol, and (epi)catechin were found. These compounds may be responsible for the starch hydrolase inhibition activity. Ethyl acetate (EA) extract of P. viridiflora stem was incorporated into wheat and rice flour to reformulate noodles with slow digestibility and was assessed under in vitro simulated gastrointestinal conditions. A dose-dependent effect on digestibility was observed for both noodles upon incorporation of 1-6% (w/w) of EA extract, with noodles containing 6% (w/w) extract exhibiting the greatest reduction in digestibility. As compared to rice noodles containing 6% extract (31.16% inhibition), wheat noodles with the same extract concentration had a smaller decline in digestibility (27.25% inhibition) after 180 min. Overall, our findings highlight the potential of P. viridiflora in the prevention of postprandial hyperglycaemia.
Highlights
The incidence of type 2 diabetes is increasing at an unprecedented rate worldwide partially due to the increased prevalence of obesity and ageing
During the initial stage of our collaboration, we conducted a screening of 25 different plant extracts from Sarawak Biodiversity Center for their starch hydrolase inhibition activity and we found that the ethyl acetate extracts of P. viridiflora extracts exhibited the strongest αamylase and α-glucosidase inhibition effects
Since the IC50 values are dependent on many factors such as enzyme origin, the concentration of substrates and other factors like pH, temperature and the buffer being used, it is more accurate to compare the acarbose equivalent (AE) values instead
Summary
The incidence of type 2 diabetes is increasing at an unprecedented rate worldwide partially due to the increased prevalence of obesity and ageing. Starch is rapidly degraded by starch hydrolases after a meal, thereby causing an elevated blood glucose level which is defined as postprandial hyperglycaemia (PPHG) [2]. This metabolic disorder is a great concern since a high blood sugar level may lead to Psychotria viridiflora Inhibits Starch Digestibility complications such as cardiovascular disease, retinopathy, and amputation [3]. Antidiabetic drugs such as acarbose are commonly used to prevent postprandial hyperglycemia by slowing down starch digestion. There is a need to explore other starch hydrolase inhibitors, most preferably from natural origins that lack the undesired symptoms
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