Sweetening agents from natural sources.

Sweetness is an important taste sensation to humans. The absence of suitable sweeteners as alternatives to cyclamates and saccharin has led to a renewed interest in sweeteners form natural sources. A brief review of the history of sweetener usage provides a basis for understanding our present heavy consumption of sweet substances. The structure of naturally-occurring compounds possessing a sweet taste range from simple sugars to complex, intensely sweet proteins. The structural types include monoterpenes, diterpenes, triterpenes, flavonoids, steroid saponins, dipeptides, and proteins. Some of these substances are not, strictly-speaking, natural but are derived from natural sources by relatively minor chemical modification. The properties of two non-sweet substances, miraculin and gymnemic acid, are included because of their close relationship to the subject of sweeteners. Miraculin causes sour substances to taste sweet and gymnemic acid selectively blocks sweet taste perception. The second part of the paper presents some of the work on monellin, the intensely sweet protein from "serendipity berries" (Dioscoreophyllum cumminsii). The physico-chemical studies of monellin provide convincing evidence that it is, indeed, a protein. Structural studies using denaturants and specific chemical modifications have provided a beginning of our understanding of the molecular basis of the sweet taste of monellin.