Grape fruit contains various nutrient elements, such as vitamins, minerals, carbohydrates, edible fibers and phytochemicals. Polyphenols are the most important phytochemicals in grape because they possess many biological activities and health-promoting benefits. The phenolic compounds mainly include anthocyanins, flavanols, flavonols, stilbenes (resveratrol) and phenolic acids. Anthocyanins are pigments, and mainly exist in grape skins. Flavonoids are widely distributed in grapes, especially in seeds and stems, and principally contain (+)-catechins, (−)-epicatechin and procyanidin polymers. Anthocyanins are the main polyphenolics in red grapes, while flavan-3-ols are more abundant in white varieties.
These bioactive phenolic compounds in grape possess many biological activities, such as antioxidant, cardioprotective, anticancer, anti-inflammation, antiaging and antimicrobial properties. Thus, grape polyphenolic extracts are used in food, pharmaceutical and cosmetic industries.
Solid-liquid adsorption technology using macroporous adsorbents (resins) is being explored to concentrate polyphenols and to remove sugars (Figure 1). Synthetic resins allow adsorption of polyphenols from aqueous solution via hydrophobic binding and aromatic stacking. They desorb phytochemicals in organic solvents, such as methanol or ethanol. Because sugars do not interact with resins, they can be easily removed by water elution, achieving concentrated polyphenolic extracts from grapes.
Static adsorption tests are being carried out with different macroporous resins in order to define which has the highest adsorption and desorption efficiency. On the other hand, different experiments based on dynamic adsorption in a glass column are being in parallel to stablish the best conditions for the further scaling-up of the process.
Ana Matías, Daniel Deodato and Yolanda Gil – Project WineSense