Influence of drying methods on total phenolics, total flavonoids and antioxidant activities in the gurmar leaf (Gymnema inodorum (Lour.) Decne.) powder

The effect of different drying methods on moisture contents, total phenolics, flavonoids and antioxidant activities in the gurmar leaf (Gymnema inodorum (Lour.) Decne.) powder was studied. These drying methods were shade drying and hot air drying at 40 ∞C – 60 ∞C for 3 – 5 h. The percentage of moisture content in powder was 3.15 – 4.83 and the water activities were 0.302 – 0.407. Total phenolics, flavonoids, and antioxidant activities of the extract were analyzed. The powder was extracted by distilled water as extracting solvent with controlled temperature 80 ∞C for 45 min. The results indicated that the hot air-dried powder at 50 °C for 3 h had total phenolics, flavonoids, and antioxidant activities higher than that of the hot air-dried (40 °C for 5 h), hot air-dried (60 °C for 3 h) and shade dried powder, respectively. Total phenolic contents were 20.165, 19.800, 18.115, and 16.903 mg GAE g–1 powder, respectively. Total flavonoid contents were 5.241, 5.238, 5.024, and 4.454 mg CE g–1 powder, respectively. The DPPH free radical scavenging activities were 10.312, 9.684, 9.498, and 8.894 mg AAE g–1 powder, respectively. The ABTS+ radical scavenging activity were 8.929, 8.914, 8.844, and 8.819 mg TE g–1 powder, respectively. Total antioxidant capacities were 42.118, 39.639, 38.812, and 37.040 mg AAE g–1 powder, respectively. The reducing powers were 13.195, 13.110, 11.832, and 11.354 mg AAE g–1 powder, respectively. The drying temperature and time affected on the water-soluble phenolics, flavonoids and antioxidant activities in the water extracts of gurmar leaf powder from different drying methods.