Off-flavor of Citrus Unshu Juice caused by heat pasteurization

Part I. Carbonyl compounds of pasteurized Citrus Unshu Juice

Abstract

Off-flavor of Citrus Unshu juice caused by pasteurization was studied to examine the relation with carbonyl compounds.
2, 4-dinitrophenyl hydrazones of the carbonyl compounds formed from pasteurized juice were separated into twelve fractions by means of silica-gel column chromatography and each of fractions 1, 4, and 12 was rechromatographed with silica-gel thin-layer.
Acetaldehyde, acetone and 2-furfural were identified by means of infra-red absorption spectra and mixed melting method respectively.
Isobutyl aldehyde was recognized presumably by Rf value and coloration of spot on a thinlayer chromatogram.
Although the off-flavor of Citrus Unshu juice brought by heat pasteurization seemed to be attributed partly to those carbonyl compounds, it was suggested from the odor of a substance caught by dry ice-methanol cold trap and liquid nitrogen cold trap that further off-flavor factors were contained in a low boiling fraction.