To improve the taste of leaf lettuce (Lacutuca sativa L.) grown hydroponically, an introduction of sweetening chemicals into the plant through the roots was examined. Sweetening chemicals used in this study were steviol glycosides obtained by extracting the leaves of Stevia rebaudiana Bertoni. Glucose molecules were partially combined with the steviol glycoside molecules by an enzymatic procedure with α-glucosyltransferase.
Stebioside and rebaudioside-A were more markedly accumulated in lettuce leaves than other steviol glycosides and their introduction ratios, the ratio of the amount of a steviol glycoside contained in the plant to the amount in the volume of solution absorbed by the plant, were 0.15-0.25 and 0.8-0.11, respectively. The steviol glycosides with combined glucoses were hardly incorporated into lettuce leaves. The lettuce leaves, when treated with the steviol glycoside solutions at the concentrations of 0.5% or 1.0%, were shown to be evidently sweet and tasty by the sensory evaluation test.
