Development of technology for the production of green coffee robusta extracts (<i>Coffea canephora</i>): selection of grinding degree and extraction temperature
The aim of the study was to determine the parameters of the optimal grinding degree and extraction temperature for Robusta coffee beans ( Coffea canephora ), which allow the most complete extraction of antioxidant substances. In the extracts, the total content of phenols, flavonoids, tannins, antiradical activity by the DPPH method, and the restoring force by the FRAP method were determined. The objects of the study were extracts obtained from Robusta coffee beans, ground to a size of 0.5, 1.0, and 1.6 mm, in a solvent of 25% water/75% ethanol. The extraction temperature was determined at the optimum fineness. The variables are 20-25°С; 40-50°С, and the boiling point of the solvent. The maximum values of the total content of phenolic substances (864 mg (HA)/100 g) and the restoring force (14.04 mmol Fe<sup>2+</sup>/kg) were found in the extract of Robusta coffee with a grinding degree of 0.5. The highest values for the total content of flavonoids (492 mg (K)/100 g) were found for extracts of Robusta coffee with a fineness of 1.0. Low antiradical activity (Ec<sub>50</sub> = 5.3 mg/cm<sup>3</sup>) was found in Robusta coffee with a grinding of 0.5. The extracts heated to a temperature of 40-50°C show high values of the content of phenols (864 mg (HA)/100 g) and the restoring force (15.93 mmol Fe<sup>2+</sup>/kg). The total content of flavonoids (652 mg (K)/100 g), tannins (186.6 mg of catechin/100 g), and the lowest antiradical activity (Ec<sub>50</sub> = 0.8 mg/cm<sup>3</sup>) are observed in extracts with an extraction temperature equal to the boiling point of the solvent. These results confirm that such technological factors as the degree of grinding and extraction temperature significantly affect the extraction of antioxidant substances and should be taken into account to optimize the extraction of antioxidants from coffee, which can later be used effectively as ingredients for functional food products.