Chemical compounds and antioxidant activity in caffeinated and decaffeinated green robusta coffee beans enriched with ginger extract

Some detrimental effects of decaffeination process are attributed to the stability of the chemical composition of green coffee beans, include reducing the antioxidant activity. Ginger ( Zingiber officinale ) is widely used as an ingredient for herbal beverage due to its well-known antioxidant activity. The aim of this study was to evaluate the effect of decaffeination process on the chemical compounds and antioxidant activity of green robusta coffee beans without or with ginger extract. The result disclosed that the total phenolic contents of decaffeinated- and caffeinated- coffee were significantly higher up to 1.13 and 3.13 mg GAE/mL, respectively, as the increase of ginger extract concentration of 30%. Of the highest concentration of ginger extract, the total flavonoid contents of decaffeinated- and caffeinated- coffee increased up to 2.55 and 13.41 mg QE/mL, respectively, as well as the melanoidin contents, rose until 0.53 nm (decaffeinated coffee) and 1.19 nm (caffeinated coffee). The analysis also found that the highest antioxidant activity determined by 2,2-Diphenyl-1-picrylhydrazyl was observed in the decaffeinated- and caffeinated- coffee (0.20 and 0.46 mmol TEAC/mL, respectively) with the addition of 30% ginger extract. When 30% ginger extract was added into the decaffeinated- and caffeinated- coffee, there was a significant improvement in the antioxidant activity tested by ferric reducing antioxidant power (0.27 and 0.77 mmol TEAC/mL, respectively) and hydroxyl radical scavenging assay (2.10 and 2.66 mmol TEAC/mL, respectively). Regardless of the concentration of ginger extract, this study reveals that decaffeinated coffee has lower antioxidant activity since a lower content of polyphenol, flavonoid, and melanoidin.