Grapeskin extract is soluble in water and water/ alcohol, but not in fats and oils. The colorant will slowly oxidize in aqueous solutions and the addition of ascorbic acid does not help. The colorant is very susceptible to pH changes and in a practical sense, is only used in products that are acidic in nature, i.e., pH 4 or below. There is gradual color change from red to blue-red, purple, steel blue, gray-green to dull yellow as the pH increases from 1 to 13. The pH not only affects color, but color intensity and color stability, each being best at pH 1 to 3.5. Stability to heat appears to be temperature dependent and long-term heating, even at low temperatures, will degrade the colorant to a brown precipitant. It reportedly can survive through jam, jelly and fruit canning processing as well as HTST. Cations, such as iron and copper, can cause discoloration and precipitation.
A protective effect is observed at high sugar concentrations, probably a function of reduced water activity. Spray-dried powders with water activity less than 0.3, for example, are stable at room temperature for over one year. Low sugar levels in high water content products, conversely, accelerate breakdown. The presence of fructose has been reported to increase browning considerably faster than glucose or sucrose. Grapeskin is unstable to UV and visible light exposure.
It was discovered that doubly acylated anthocyanin mixtures exhibited better stability to light, heat and oxidation than the mono-acylated anthocyanins obtained from grapeskins. A search for plant materials with high levels of naturally occurring doubly acylated anthocyanins led to grape varietal selection and to other anthocyanin containing vegetables, such as purple carrot, elderberry, red cabbage and red raddish. These sources are now commercially available from Nutra Food Ingredients .Grapeskin extract has found application in water-based acid beverages, jellies, candy, gelatin desserts, skin and hair care products, dry mixes, dark chocolate and cake mixes.