High-field proton NMR studies of apple juices

Abstract

High-field (11.7 and 14 T) proton high-resolution NMR spectra of apple juices obtained from a variety of cultivars are reported and partial spectral assignments are made. There are significant spectral differences between cultivars, which may be of value in identifying the origins of apple juices. The results also indicate that the method is likely to be of value in the authentication of fruit juices. Careful spectral analysis shows that some differences arise simply as a result of the differences in the pH of the juices and that microbiological and oxidative effects must be taken into account. Care must therefore be exercised in the application of multivariate methods to the data as spurious or trivial correlations may be obtained. It is concluded that the richness of the spectra and the ease with which they may be obtained indicate that high-field proton NMR will prove valuable not only in speciation and authentication studies, but also in the analysis of biochemical changes occurring in fruits and their juices. © 1997 John Wiley & Sons, Ltd.