Estimation of aroma glycosides of nutmeg and their changes during radiation processing

Abstract

Glycosidically bound volatile compounds of nutmeg were identified as glyco-conjugates of p-cymene-7-ol, eugenol, methoxyeugenol and alpha-terpineol. Using phenyl-beta-glucoside as external standard the contents of these glycosidic precursors were estimated based on the measurement of TLC spot density on a densitometer. p-Cymene-7-ol rutinoside was the major aroma glycoside (3.15 mg/100 g), followed by glucosides of methoxyeugenol (0.61 mg/100 g), eugenol (0.50 mg/100 g) and alpha-terpineol (0.51 mg/100 g). A dose-dependent breakdown of these glycosidic precursors was observed during gamma-radiation processing. Among the four glycosides, alpha-terpineol glucoside was the most sensitive to radiation while p-cymene-7-ol rutinoside was the least sensitive. A reduction in the content of total glycosides by almost 50% was noted at a dose of 5kGy. Partitioning of aroma glycoside into n-butanol from aqueous extracts was found to result in rapid isolation of aroma glycosides, avoiding time consuming pre-purification on Amberlite XAD-2 column. A routine method based on extraction into n-butanol and subsequent quantification of post-irradiation changes in aroma glycosides on a TLC plate using a densitometer is proposed.