The genus Vitis belongs to the family Vitaceae and comprises two subgenera, the Euuitis (true grapes), also called “bunch grapes”, and Muscadiana, which grow as separate berries (). The subgenus Euvitis is divided into fewer than 60 species. By far the most economically important species is Vitis vinifera, which is native to the area of Asia Minor south of the Black and Caspian seas. The United States has more different native species than any other country/Two species of Muscadinia are native to the southeast (Vitis rotundifolia and Vitis munsoniana), but the most native American vines are Euvitis species. In the latter group, the only one used much in wine-making today is Vitis labrusca. However, several native American species are parents of hybrid grape varieties used as wine grapes or grape rootstocks.
Grapes are the most important fruit crop grown in the world, exceeding in quantity all other fruits combined. Most of this crop is destined for wine, but a significant amount is also used for juice products. Processing grapes into both wines and juices yields a sizable amount of grape press residue or pomace. Potentially the most valuable component of grape pomace are the anthocyanin pigments (). In fact, grape pomace is one of the least expensive and most available sources for anthocyanin-based colorants (). Both a spray-dried powder and a concentrated solution containing grape anthocyanins are marketed for use in foods, beverages, and cosmetics (). However, pigment recovery from the fresh fruits involves such limitations as seasonal availability of raw materials, fresh material losses, variations in composition, and pigment degradation caused by storage and extraction process. Cell suspension cultures, on the other hand, allow a more direct pigment production in amounts equal or superior to those of intact fruits (). The emphasis of this chapter will be on the use of grape (Vitis vinifera L.) cell culture for the direct production of anthocyanin-based colorants.
In 1987, the world market for food colorants was estimated at $320 million (). While the market for synthetic colorants was $200 million, that for carotenoids including synthetic nature-identical was $35 million. All other natural colorants, including anthocyanins, represented a $35 million market. The market for natural colorants is in rapid progression catalyzed by concerns over the safety of synthetic food colorants.
Concern for safety is the one universal commonality among food colorants. In fact, in the past, the only food colors to have been banned have been artificial. This has happened on the basis of toxicological studies, which have shown only positive results for natural colors to date (). With respect to artificial red colors, FD&C Red No. 2 or amaranth has been banned since 1976 since it could be shown in animal experiments that it may cause cancer. A similar situation occurred in January of 1990, when the Food & Drug Administration announced the formal banning of FD & C Red No. 3 lake (erythrosine) in foods, drugs, and cosmetics (). In future, the requirements for food additives will become still more stringent. Therefore, the trend to the less problematic natural additives will probably continue.
Disadvantages of natural food colorants include unreliable supply dependent upon weather and seasonal variability in the plant material and resultant color compounds and strong undesirable flavors. Plant tissue culture offers a very promising avenue that would overcome these disadvantages (). In the particular case of anthocyanins, the availability of large quantities of colorants of consistent composition might be the biggest hurdle to overcome (). With the current knowledge, we could envisage establishing a production process in which yield and composition of anthocyanin would be consistent. However, basic understanding of the regulation of anthocyanin biosynthesis at the sub-cellular level is required to unveil the full potential of plant cell-based bioprocesses. Furthermore, to cultivate plant cells on a larger scale than has ever been accomplished requires that studies also be conducted in the area of biochemical engineering.
Selections from the book: “Medicinal and Aromatic Plants V”, 1993.