Simultaneous recovery of bioactive compounds from winemaking by-products by green subcritical fluids

The food industry generates large amounts of by-products. Most of these biomasses are disposed of in landfills, contributing to climate change through greenhouse gas emissions, water and soil contamination. Several strategies have been proposed to reduce their environmental impact and convert these biomasses into valuable economic resources. In this context, the extraction of valuable compounds with technological or healthful properties from food by-products has gained significant interest. Several extraction methods are available. Conventional methods have several drawbacks, and several innovative processes were proposed. Subcritical Fluids Extraction (SSE) may be considered one of the most promising and versatile. A compound is defined as being in the subcritical state when its temperature is increased between its boiling and critical points, and its pressure is high enough to maintain the liquid state. Increasing temperature and pressure improve extraction rates and process efficiency through several mechanisms. The present study aims to evaluate SSE for extracting bioactive compounds from grape marc, the most abundant solid by-product of winemaking, using different green solvents: water, ethanol, and a 50% water-ethanol mixture. The effect of temperature (120, 150, and 180 °C) was also evaluated. A technological comparison, based on the mathematical modelling of extraction curves, and a chemical comparison between SSE and conventional extraction (CSLE) were considered. The best extraction conditions were obtained with the ethanol-water mixture at subcritical conditions, allowing the simultaneous extraction of polyphenols, proteins, and polysaccharides. Increasing the SSE temperature resulted in a 3-fold increase in polyphenols, an 8-fold increase in proteins, and a 15-fold increase in polysaccharide content compared to CSLE. The mathematical modelling of the extraction curves revealed that SSE was, on average, eight times faster. Moreover, the subcritical conditions positively affected some chemical properties of the extracted solutes, which may be related to the increase in antioxidant activity of SSE extracts.