|Authors: ||K. Rungruchkanont, Y. Chatsuwan|
|Keywords: ||orchid, antidiabetic medicine, DPPH free radical scavenging activity, half maximal inhibitory concentration (IC50)|
Grammatophyllum speciosum Blume is the largest epiphytic orchid.
In Thailand, it is used to prepare a herbal elixir against inflammation.
This study determined antioxidant activity and α-glucosidase inhibitor activity in ethanol extracts prepared from leaf, rhizome+root and pseudobulbs of 3 different age plants: 6-year-old plants, 1-year-old plants and in vitro plantlets.
For 1-year-old plants and in vitro plantlets, only 2 parts, leaf and rhizome+root, were used.
The experimental design was a completely randomized design.
The experiments were done in duplicate and measurements were applied in triplicate (n=3). After extraction of fresh and dried samples, antioxidant activity and α-glucosidase inhibitor activity were determined.
Extractions from fresh samples of 6-year-old leaf and rhizome+root parts yielded the highest DPPH free radical scavenging activity (77.68 and 76.95%, respectively), but were not different from Trolox, 100 μg mL‑1, the positive control (83.85%). The IC50 value of the DPPH extract from 6-year-old leaves and rhizomes+roots and Trolox were 32.07, 17.87 and 7.43 µg mL‑1, respectively.
For α-glucosidase inhibitor activity, extractions from 6-year-old rhizome+root (both fresh and dry samples) showed strong activity (84.88 and 85.47%, respectively) and were significantly lower than acarbose, 1 mg mL‑1, (positive control, 94.50%). The other plant samples had weak activity (8-13%). The IC50 value of α-glucosidase inhibitor activity in extracts from 6-year-old rhizome+root (fresh sample) and acarbose were 443.52 and 390.42 µg mL‑1, respectively.
Results suggested that 6-year-old rhizome+root of G. speciosum could be a potential source of natural antidiabetic medicine.
The 6-year-old leaf and 6-year-old rhizome+root could be sources of antioxidant.
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