Polyvinylalcohol Stabilizes Anthocyanins of Red Wine in the Solid Phase but Not in the Aqueous Phase

Abstract

Monomeric anthocyanins exhibit color variations at different pH, but they are highly unstable at physiological pH. To improve the stability, the effects of polyvinylalcohol on the anthocyanins of young red wine prepared from Cambell Early grapes were examined in aqueous solution and in the solid phase on a cotton swab® and inert materials. Cyanidin-3-glucoside and mal-vidin-3-glucoside represented approximately 43.6% of total anthocyanins in the red wine. The anthocyanins decreased to 11.3% of the initial amount in aqueous solution at physiological pH after storage for 60 days at room temperature. On the other hand, from 66.9% to 87.2% remained in the solid phase on a cotton swab® and polypropylene membrane in the presence of polyvinylalcohol. The stability of the anthocyanins increased with the concentration of polyvinyl-alcohol in the solid phase but not in the aqueous solution. The anthocyanins were found to be condensed and immobilized in the complexes of anthocyanins and polyvinylalcohol on the poly-propylene membrane by phase-contrast microscopy analysis. The anthocyanins in the cotton swab® displayed color variations when dipped into different pH buffer solutions. These results suggest that anthocyanins from red wine stabilized in the solid phase by polyvinylalcohol can be used as a visual indicator of pH.