Microwave pretreatment to improve extraction efficiency and polyphenol extract richness from grape pomace. Effect on antioxidant bioactivity

[Display omitted] •Microwave intensification pretreatment for grape pomace polyphenol extraction.•Simultaneous high polyphenol yield and richness are obtained.•The differentiated extraction rates lead to a polyphenol richness optimum.•Anthocyanin product richness is boosted by microwaves.•Polyphenol and anthocyanin rich extracts have higher cellular antioxidant activity. Microwave assisted extraction advantages are widely recognised. However, its implementation at industrial scale is restricted due to microwave limitations. In this work, a microwave pretreatment is proposed as an easy scale-up alternative for grape pomace polyphenol extraction, especially for anthocyanins. The double effect of this pretreatment on extraction yield and on product richness is assessed. Microwaves accelerate the extraction kinetics of most compounds, but their effect on polyphenols is more pronounced than in other substances (like sugars and fibres). These differentiated rates are exploited to improve the polyphenol richness of the final dry product. By selecting the appropriate operating conditions, polyphenol yield was increased by 57% and, simultaneously, dry product richness was enhanced by 32%. Also, anthocyanin extraction boost was remarkable. Its content in the final dry product was 85% higher than the one obtained without the microwave pretreatment. The cellular bioactivity of these extracts was improved by 83% and 133%.