Chemical and Sensory Changes in Flavor of Roux Prepared from Wheat Flour and Butter by Heating to Various Temperatures

Abstract

The flavor of an unheated wheat flour and butter mixture (roux 0) and roux samples heated to between 100°C and 180°C at 20°C intervals (roux I–V) were examined by chemical analyses of the aroma components with gas chromatography (GC) and GC-MS and sensory evaluation of the roux samples. In the chemical analysis, it was determined that large quantitative changes of aroma components with increased heating temperature occurred in the functional groups of ketones, carboxylic acids, furans and pyrazines. Furthermore, a cluster analysis showed that the difference in characteristic flavor between roux II (white roux) and roux IV–V (brown roux) depended on the quite different compositions of their components. On the other hand, sensory analysis of the roux showed that roux II–IV (heated to 120°C–160°C), namely white and brown roux, were highly evaluated for buttery and sweet attributes as well as odor preference. After the relationship between chemical and sensory changes in the roux flavor with increased heating temperature was surveyed by a principal component analysis, a correlation analysis clarified that the sensory odor preference correlated significantly with ketones (mainly methyl ketones) (r=0.900, p<0.05) or with cyclic ketoenols such as maltol (r=0.838, p<0.05). Those compounds also showed a high positive correlation with the evaluation for the sweet attribute. Therefore, methyl ketones or cyclic ketoenols are assumed to play an important role as indicators of the pleasant odor preference in roux heated to various temperatures.