The International Diabetes Federation reported that by 2035 the expected increase in
diabetes in sub-Saharan Africa will be 109%, the highest rise in the world. Furthermore,
almost a quarter of the world‘s adult population have the metabolic syndrome. One
therapeutic approach for type 2 diabetes (T2D) treatment is to inhibit digestive amylases
and thereby decrease post-prandial hyperglycaemia. Polyphenols like sorghum condensed
tannins (SCT) inhibit α-amylase and α-glucosidase enzymes. However, orally administered
SCT may have poor inhibitory action against amylases, due to non-specific protein
binding. Research is required to determine how to effectively deliver SCT to the small
intestine to inhibit digestive amylases and decrease post-prandial hyperglycaemia.
This study investigated the encapsulation of SCT in kafirin microparticles (KEMS) using
aqueous ethanol and acetic acid coacervation methods. The inhibitory action of SCT on α-
amylase and α-glucosidase were compared to acarbose (standard drug). The inhibition of
SCT-KEMS after simulated gastrointestinal digestion was assessed. Electron microscopy
was used to characterise microparticle morphology. A confirmatory in vivo test was
performed using an oral starch tolerance test (OSTT) on healthy rats.
SCT were about 20 000 times more effective at inhibiting α-glucosidase (IC50 = 0.4 μg/ml)
than acarbose (IC50 = 8464.0 μg/ml), while acarbose (IC50 = 3.1 μg/ml) inhibited α-amylase
better than SCT (IC50 = 554.5 μg/ml). The aqueous ethanol method of encapsulating SCT
resulted in higher encapsulation efficiency (48%) than the acetic acid method (25%).
Electron microscopy and quantitative data showed that SCT-KEMS were hardly digested
by pepsin and trypsin-chymotrypsin during simulated digestion. SCT-KEMS retained their
inhibitory activity against both amylases after simulated digestion, while SCT alone lost most of their inhibitory activity. In vivo data showed that the SCT-KEMS treatment
decreased the maximum blood glucose level of rats by on average 11.8% and the area
under the curve by 9%, compared to the water control. Acarbose decreased the blood
glucose spike of the rats by on average 18.5% compared to the control. SCT-KEMS and
acarbose did not elevate serum insulin levels and actually decreased insulin secretion by
60% and 48%, respectively, compared to the control.
These findings indicate that KEMS are effective SCT encapsulating agents as they deliver
the SCT to the small intestine. SCT-KEMS prevents hyperglycaemia by inhibiting
digestive amylases and seems to substantially reduce insulin secretion when carbohydrate
is consumed. Therefore, SCT-KEMS could be employed as a nutraceutical to inhibit
digestive amylases and thereby attenuate post-prandial hyperglycaemia associated with the
metabolic syndrome and T2D.