Tartaric acid recovery from winery lees using cation exchange resin: Optimization by Response Surface Methodology

• Tartaric acid recovery from wine lees using cation-exchange resin under mild conditions.
• Concurrent separation of stream rich in polyphenolic compounds for further exploitation.
• Assessment of main parameters and their interaction in determining optimum conditions.
• Central Composite Design (CCD) with Response Surface Methodology (RSM) employed.
• Process pH, water and resin dosage values optimized and experimentally validated.

A crucial first step in developing a novel cost-effective and environment-friendly process for recovering tartaric acid and bioactive polyphenolic compounds from wine lees involves tartrates dissolution by mild means, aiming to maximize tartaric acid recovery, while minimizing the concentration of undesirable potassium. Such a processing step, using cation exchange resin, has been systematically assessed to obtain a set of near-optimum values of the key variables (i.e. pH, water dosage and cation exchange resin dosage). An experimental design was carried out based on Central Composite Design (CCD) with Response Surface Methodology (RSM) to evaluate the effects of process parameters and their interaction towards the attainment of optimum conditions. All three variables considered were found to be significant; however, the most influential factor for maximum tartaric acid concentration was the volume of added water, whereas for potassium removal the cation exchange resin dosage. A quadratic model was developed that fitted well to the experimental data confirmed by the high R2 values, greater than 0.98. A set of optimum values of the three main variables was determined to be pH = 3.0, water dosage 10 ml/g dry lees and resin dosage 3.5 g/g dry lees. Under these optimum conditions, the predicted tartaric acid and potassium concentration were 43,143 ppm and 178 ppm, respectively, which correspond to 74.9% tartaric acid recovery and 98.8% potassium removal. Furthermore, the corresponding experimental values, from the validation experiment, fitted well to these predictions. This work clearly shows that the recovery of tartaric acid from wine lees can be achieved using cation exchange resin, under mild conditions (ambient temperature) avoiding the waste calcium sulfate sludge of the conventional process.