Chemical and sensory variability in table grapes

Abstract

Introduction Consumer acceptance of grapes is based on a number of factors, including color, flavor, size, bloom, and texture. This study is concerned directly with the first two factors only, although textural changes associated with the maturity level of the fruit could possibly influence over-all sensory impressions. Flavor is defined as the complex reaction of taste and olfactory receptors; the olfactory aspect is believed to be secondary with non-muscat varieties. In this study, only the taste aspect of flavor will be considered. There are four possible tastes in grapes: acidness (tart, or sour), sweetness, saltiness, and bitterness. White grapes are very low in tannins and other bitter-tasting substances. Red grapes have more bitter-tasting substances, but these are mainly in the skins and unless skins are vigorously chewed little bitter taste is experienced. Grapes have very little salty taste, though tartrates give a reaction. Tartrates as buffer agents repressing the ionization of malic and tartaric acids may, however, influence the acid taste. The characteristic gustatory sensation of grapes is their sweet-sour taste. The main sugars found in grapes, levulose and dextrose, are of very unequal sweetness (about 1.5:1) and presumably the ratio as well as the total amount of the two may be of importance to the sweet taste (Amerine and Thoukis, 1958).2 The acid taste is produced by the organic acids, chiefly tartaric and malic, whose relative as well as total amounts in the fruit are influenced by the variety and by the temperature during the ripening period; these acids are of unequal sourness. For a discussion of the effect of variety, region, and time of maturity on the tartrate/malate ratio see (Amerine and Winkler (1942)). Color is particularly significant as an acceptability factor in table grapes as it is the primary factor of the grapes’ appearance, and appearance is of prime importance. In fact, color is usually used as an index of maturity in red and black grapes (United States Code of Federal Regulations, 1962). Its significance in white grapes is much less clearly defined, however. The subtle changes in color from grass-green to yellowish-amber as maturity advances are much less pronounced than with pigmented fruit, but there are strong indications that consumers do detect these color differences, associating the yellow tones with greater sweetness. The importance of the other appearance factors—size and shape of berry, amount of bloom, etc., have not been investigated thus far. It would also be desirable to have information on the importance to