Recovery of grape pomace phenolic compounds through optimized extraction and adsorption processes

The objective of this work is to optimize an efficient green technique for the extraction of phenolics from grape pomace. Two extraction techniques, ultrasound- and microwave-assisted extraction have been used. In ultrasound extraction, temperature (20 - 60 degrees C), solvent type (0-100 % v/v aqueous ethanol), amplitude (20-60 %), and solvent/solid ratio (8 - 24 mL/g) were the factors investigated. In the case of microwave extraction, the effects of solvent type (0-100 % v/v aqueous ethanol), solvent/solid ratio (8 - 24 mL/g), and power (100-600 Watt) were studied. In addition, the effect of pomace moisture content was studied under the optimum conditions. Another objective was to study the enhancement of the optimum procedure by enzymatic pretreatment using two enzymes, cellulase and pectinase, under different conditions (enzyme concentration, 2-4 % w/w; time, 60 - 240 min; water/solid ratio, 2/1-6/1 mL/g). The optimum extraction yield (48.76 mg GAE/g dry pomace) was achieved using ultrasound extraction at 56 degrees C, a solvent/solid ratio of 8 mL/g, an amplitude of 34 %, and a time of 20 min with 53 % v/v ethanol, after pretreatment with cellulase, at a concentration of 4 % w/w, time of 240 min, and water/pomace ratio of 2 mL/g. Furthermore, in order to obtain phenolics in a purified form, adsorption was carried out with zeolite.