Grapeskin Extract

Grape is the single most abundant fruit harvested in the world from which a natural color is commercially obtained. Grapes are highly pigmented with anthocyanins, a pool of colorants responsible for the purple, violet, blue, magenta, red and orange color of many fruits, vegetables and flowers. Anthocyanins are often extracted from the grape skin remaining after wine crushing or from "leas," the sediment at the bottom of barrels from the wine aging process. Most recently, additional sources of anthocyanins have become available, from grape juice of selected varieties, from vegetable juice extracts (cabbage and carrot), and from other berries (Aronia).

Grapeskin extraction is carried out using a dilute aqueous solution of an acid, usually sulfurous acid. The extract is made up of various anthocyanins, sugars, acids and salts. It is usually concentrated to a viscous thick liquid of about 20-30° Brix, containing about 0.5 to 1.5 % anthocyanin content. This liquid can be spray dried, most often with maltodextrin as a carrier. The powder can average 4% anthocyanin. There are two forms of grapeskin extract available commercially (liquid and powder). The extract is purchased not on the anthocyanin content, but on color strength (absorbency / gm), a measurement used to standardize batches. The differences observed between batches/supplier are a function of variety, source, condition of extraction, and the anthocyanin makeup of the extract. These variables, as well as the properties of the product to be colored, will dictate the functionality of grape skin and its stability.

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 ColorMaker.

Grapeskin extract has found application in water-based acid type beverages, jellies, candy, gelatin desserts, skin and hair care products, dry mixes, dark chocolate and cake mixes.

Molecular Structure

(A) Red Anthocyanin (Malvidin-3,5-diglucoside)

(B) Yellow Flavonoid

(C) A Component of Tannin

(D) Phenolic Acid, Caffeic Acid

(E) Stilbene Phytoalexin, Resveritold