Discrimination between Orange Juice and Pulp Wash by 1H Nuclear Magnetic Resonance Spectroscopy: Identification of Marker Compounds

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Abstract
The potential of NMR spectroscopy and multivariate analysis methods to detect the adulteration of orange juice with pulp wash is demonstrated. Principal component analysis has been applied to 1H NMR spectra of >300 orange and pulp wash juices, and stepwise linear discriminant analysis was used to classify the samples. A model with six principal components gave a high success rate of classification (94%) for both training and validation sets. An important principal component loading showed that dimethylproline played a key role in the discrimination between the two types of juice, with higher levels in pulp wash. Dimethylproline was not previously known as a marker compound for orange juice adulteration. An ANOVA test revealed at least 21 other NMR signals that differed significantly between the authentic and pulp wash groups. The compounds they represent could be seen as potential marker compounds in addition to dimethylproline. This makes NMR with chemometrics an attractive screening tool with advantages in terms of rapidity, simplicity, and diversity of information provided. Keywords: NMR; orange juice; pulp wash; authenticity; adulteration; multivariate analysis