Determination of Rosin Ester Gum Emulsifiers in Fruit Juices by Gas Chromatography

Abstract

A method for detection and determination of rosin ester gum in fruit juice was established as follows. Rosin ester as a component of ester gum was extracted with benzene from the sample, and saponified with N/2 KOH-ethanol solution. The rosin acids were extracted with diethyl ether in acidic condition, derivatized with TMS reagent and determined by gas chromatography (GC). Seven kinds of ester gum standard were analyzed by the proposed method, and it was found that contents of dihydroabietic acid and abietic acid in the ester gums ranged between 33.8–75.1% and 0–36.7%, respectively, but the total contents of them were 66.7–75.1% (average, 70.9 ± 3.0%). Dihydroabietic acid and abietic acid derived from ester gum in 6 kinds of imported fruit juice were identified by GC-mass spectra and quantitated by GC. The contents of ester gum in samples estimated from the two peaks were 15.2–33.9 ppm. Recoveries of ester gum added to sample at 50 and 500 ppm were more than 92.7%, and the detection limit of ester gum was 0.5 μg (2 ppm in sample) by the proposed method.