Quantitation of free and glycosidically bound volatiles in and effect of glycosidase addition on three tomato varieties (Solanum lycopersicum L.).

The volatile fractions of three tomato cultivars (p73, Jorge, and Durinta) were studied in both free and glycosidically bound forms. The possibility of increasing the concentration of free volatile compounds by adding selected glycosidases was also tested. The free volatile fraction (FVF) of tomato juice was directly determined by headspace solid-phase microextraction (SPME). To analyze the glycosidically bound fraction (GBF), tomato juice samples were extracted with C18 cartridges and the resulting glycoside extracts were enzymatically hydrolyzed. The released aglycons were determined by headspace SPME. Of these compounds, six were not previously reported to belong to the tomato GBF. The concentration of 21 of 24 compounds detected in the FVF was significantly different between cultivars, the majority of them being greater in p73 than in Durinta and Jorge cultivars. In the GBF, 19 of 26 compounds that were detected were significantly different between cultivars but only the amount of trans-linalool oxide was significantly the greatest in the p73 cultivar. The addition of Candida molischiana beta-glucosidase (BGLN) and Saccharomyces cerevisiae exoglucanase (EXG1) to tomato juice samples led to increases in the concentration of 10 compounds, with variations depending on the cultivar or enzyme. These results provide scientific support for using glycosidases as a tool to improve tomato aroma.

Quantitative comparison of free and bound volatiles of two commercial tomato cultivars (Solanum lycopersicum L.) during ripening.

The changes in the profile of both free and glycosidically bound volatiles were studied in Moneymaker and Raf tomato cultivars during fruit ripening. The concentrations of 20 of 24 and of 27 of 30 compounds detected in the free volatile fraction (FVF) and glycosidically bound fraction (GBF), respectively, differed significantly between cultivars during ripening. Most free and bound volatiles increased during ripening in both cultivars. The contribution of each free volatile compound to the overall aroma was estimated by calculating its log U value, which indicated that only 11 compounds seem to exert a strong influence. Nine volatiles were detected exclusively in the GBF, among them geraniol, beta-citronellol, alpha-terpineol, and trans- and cis-linalool oxides. Nine other compounds were found to be more abundant in the GBF than in the FVF, their absolute levels varying between cultivars and stages of ripening. According to the log U values reached, of these nine compounds, linalool, 3-methyl-1-butanol, trans-2-hexenal, eugenol, and 2-phenylethanol may have an impact on tomato aroma upon release from their glycosidic conjugates. Sugars resulting from the enzymatic hydrolysis of the GBF were detected by high-performance liquid chromatography. Rhamnose was the most abundant followed by arabinose, glucose, and xylose.