Valorization of grape pomace: Drying behavior and ultrasound extraction of phenolics

- The drying behavior of grape pomace was studied.
- The kinetics of phenolics degradation during drying of grape pomace was studied.
- The ultrasound-assisted extraction of phenolics from grape pomace was studied.
- The effect of different parameters on extraction yield was studied.

The wine industry generates huge amounts of grape pomace as an industrial waste. Recently, there has been much interest in the phenolic compounds of grape pomace, because of their health benefits, such as antioxidant activity, acting as free radical scavengers, and inhibition of lipoprotein oxidation. Thus, the objective of this work is to optimize a new method for grape pomace application in food industries based on the ultrasound-assisted extraction of phenolics compounds. Dehydration of grape pomace is the first step before extraction. Thus, another subject of this work is to study the drying behavior of this winery by-product and the kinetics of total phenolics degradation during the drying process. Drying (moisture vs time) data were obtained on slabs of grape pomace in an air dryer operating at 60-85 °C. The effective diffusivity was determined using the method of slopes of the drying curve taking into account the effect of moisture content on diffusivity. The combined effect of moisture content and temperature on effective diffusivity was expressed by an empirical model. In addition, each moisture loss curve was fit to empirical simplified drying models. Finally, the effects of solvent type, extraction temperature, solvent/solid ratio, amplitude level, and pulse duration/pulse interval ratio on the yield of phenolics extraction were studied.

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