Impact of an integrated process of hot pressurised liquid extraction–macroporous resin purification over the polyphenols, hydroxymethylfurfural and reducing sugars content of Vitis vinifera ‘Carménère’ pomace extracts

Thermal degradation and generation of objectionable compounds such as hydroxymethylfurfural have been observed in hot pressurised water extraction of polyphenols. Addition of small amounts of ethanol can reduce process temperatures and retain extraction efficiencies. However, ethanol may reduce the recovery of polyphenols in the subsequent purification stage. The overall effect of increasing amounts of ethanol (0–15%) and reduced temperatures (90, 75, 60 °C) in the extraction stage, as well as increasing amounts of ethanol in the desorption eluent (60–80%) were analysed in a combined hot pressurised liquid extraction–resin purification grape pomace polyphenols process for the first time. Without decreasing the polyphenols recovery (~24 mg GAE g⁻¹), ethanol addition (15%) reduced the extraction temperature (from 130 to 90 °C) which not only decreased the reducing sugar extraction (~25%) but also avoided the hydroxymethylfurfural generation in the extraction stage. Additionally, the combined hot pressurised liquid extraction–resin purification process preserved the proanthocyanidin oligomeric distribution and was selective to polyphenols. The operating conditions found for the combined process, efficiently produced purified polyphenols extracts (11 mg GAE g⁻¹), free of hydroxymethylfurfural and reducing sugars.