Optimization of Phenolic Content, Antioxidant, and Inhibitory Activities of α-Glucosidase and Angiotensin Converting (AC) Enzymes from Zingiber officinale Z.

The optimum extraction conditions of phenolic compounds from ginger were evaluated with respect to antioxidant activity and angiotensin converting enzyme and alpha-glucosidase inhibitory activities. Free phenolics were extracted under conditions that varied according to extraction time, temperature, and solvent type (water, acetone, and methanol). Acid and base hydrolysis reactions were used to obtain bound phenolic compounds from ginger. The results showed that the type of solvent used and the temperature and time of extraction needed for maximal total phenolic content, antioxidant activity, and angiotensin converting enzyme inhibitory activity differed greatly from solvent conditions and showed the greatest alpha-glucosidase inhibitory activity. The predominant free phenolics in the methanol extracts included diosmin, thymol, and carvacrol, which varied greatly according to solvent extraction conditions (i.e., time and temperature). Diosmin was the predominant bound phenolic compound of the methanol extracts. The present study findings indicate that differing solvent extraction protocols involving extraction time and temperature for ginger need to be explored to generate specific optimal bioactivities of the extracts, which are related to the pattern of predominant phenolics in those extracts.