Evaluation of the Antioxidant Capacity of Deep-frozen Green Coffee and Roasted Coffee

Abstract

There is little information on the antioxidant composition of green or roasted coffee. This work evaluated the antioxidant capacity (AC) and the content of total phenolic compounds (TPC) in the ethanolic extracts of deep-frozen green coffee (DFGC), green coffee without deep-freezing (GCWDF), and roasted coffee (RC). The AC was evaluated by the ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid)) and DPPH (2,2-diphenyl-1-picrylhydrazyl) methods, while the content of phenolic compounds was determined by the Folin-Ciocalteau method. The average values of the AC (mmol Trolox/g coffee) were 1.35 for DFGC at a temperature interval between -40ºC and -10 ºC, 0.22 for GCWDF, and 0.15 for RC between100 ºC and 250 ºC by the ABTS method. These values correspond to a % inhibition of this radical of 90.5, 81.5, and 62.3, respectively. By the DPPH method, the AC (mg caffeic acid/g coffee) was 21.31 for DFGC, 20.91 for GCWDF, and 7.72 for RC. These values correspond to a % inhibition of this radical of 94.4, 94.4, and 87.6, respectively. The TPC content (mg gallic acid/g coffee) was, on average, 158.4 for DFGC, 132.6 for GCWDF, and 99.3 for RC. To know the content of antioxidant compounds considering the rate and speed at which they can be extracted, the effective diffusion coefficient (Deff) in m2/s, and the first-order kinetic constant (k) in s-1 of the TPC extraction process were also determined. The results of Deff were 6.8 10-11, 4.7 10-11, and 5.83 10-11, and those of k were 2.15 10-3, 1.57 10-3, and 1.58 10-3 on average for DFGC, GCWDF and RC, respectively.