Application of multivariate statistical methods to extend the authenticity control of flavour constituents of apple juice

The distribution of 15 aroma constituents. including the (R)- and (S)-enantiomers of ethyl 2-methylbutanoate, in 30 commercially available and laboratory prepared apple juices was evaluated by multivariate statistical methods. Principal component analysis and cluster analysis revealed ethyl 3-methylbutanoate, 3-methylbutyl acetate and (R)-ethyl 2-methylbutanoate as key components for the differentiation of apple juices. In freshly pressed and some commercial juices ethyl 3-methylbutanoate and 3-methylbutyl acetate were not present, and the (S):(R) ratio of ethyl 2-methylbutanoate was found to be >99:1%. Another group of commercial products was separated in which the amounts of ethyl 3-methylbutanoate and 3-methylbutyl acetate exceeded 1 mu g/l and 180 mu g/l, respectively, and in which the (S):(R) ratio of ethyl 2-methylbutanoate was < 97:3%. The statistical data confirmed the high selectivity of apple fruit tissue in biosynthesizing 2-methylbutyl and 2-methylbutanoate esters, and could also be used to extend the results of enantio-multidimensional gas chromatography and other authenticity analyses.