Antioxidant Activity and Phytochemicals of Freeze-dried and Spray-dried Soluble Coffee Brews

This study analyzed the antioxidant activity and the concentration of several phytochemicals i.e. polyphenols, caffeine, glutathione (GSH), and protein, of freeze-dried and spray-dried soluble coffee brews. Six types of coffee samples were analyzed i.e., 1) Spray-Dried Robusta instant coffee (SDR), 2) Freeze-Dried Robusta instant coffee (FDR), 3) Regular Robusta coffee powder (RR), 4) Spray-Dried Arabica instant coffee (SDA), 5) Freeze-Dried Arabica instant coffee (FDA), and 6) Regular Arabica coffee powder (RA). Antioxidant activity was determined using the 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) radical scavenging assay. Polyphenols, caffeine, glutathione, and protein were measured spectrophotometrically. Results showed that freeze-dried instant coffee (both robusta and arabica) in a concentration of 500 ppm demonstrated DPPH radical scavenger activity >80% and significantly higher (p<0.05) compared to spray-dried soluble coffee and regular coffee brews. This level was maintained in concentrations of 750 ppm, 1000 ppm, and 1500 ppm. The higher antioxidant activity of freeze-dried coffee brew was in line with the higher concentration of polyphenols, caffeine, GSH, and protein. In conclusion, freeze-dried instant coffee demonstrated more sensitive antioxidant activity, probably due to its more abundant polyphenols, caffeine, GSH, and protein. Key words: Caffeine; DPPH; Glutathione; Polyphenols; Protein.