Abstract:
Thebu (Costus speciosus) leaves show various biological activities such as anti-diabetic,
anti-oxidant, anti-cancer, anti-inflammatory, and diuretic activities. These activities are
provided by the bioactive compounds found in C. speciosus leaves including phenols,
flavonoids, steroids etc. The objective of this study was to optimize the extraction of C.
speciosus leaves with regard to its antidiabetic and antioxidant activity. In this study,
dried C. speciosus leaves (20 g) were macerated and extracted with water, 70%, 80%,
and 90% v/v ethanol-water mixtures at 60 ◦C for 48 hours. DPPH radical scavenging
activity, total phenolic content, and alpha-amylase inhibition activity were determined
as functional properties. Aqueous extract showed the highest yield (19.53%) and the
lowest yield was shown by 90% v/v ethanol (16.32%). Aqueous extract showed the lowest
IC50 value for amylase inhibition activity (0.68±0.034 mg/mL) followed by 80% v/v
ethanol leaf extract (0.78±0.146 mg/mL). Acarbose was used as the positive control and
its IC50 value was 0.71±0.028 mg/mL. Methanol was used as the negative control. The
90% v/v ethanolic extract showed the lowest IC50 value for DPPH radical scavenging
activity (0.06±0.008 mg/mL). Ascorbic acid was the positive control and its IC50 value
was 0.23±0.014 mg/mL. The total phenolic content of ethanolic extracts was higher
than that of aqueous extract and 90% v/v ethanolic extract showed the highest total
phenolic content 9.91±0.024 GAE (mg/g). In conclusion, 90% v/v ethanolic extract
showed the highest antioxidant activity and total phenol content. The aqueous extract
showed the highest antidiabetic activity. The antioxidant and total phenol content of
the plant extract increases with increasing the ethanol concentration. In-vivo test for
the maximum tolerable intake to consume C. speciosus based products is suggested for
further studies.
