Classification of commercial apple juices based on multivariate analysis of their chemical profiles

Currently, a wide range of differently processed apple juices is available on the market. In this study the quality of commercial apple juices from four product categories was evaluated on the basis of their chemical profiles (total soluble solids, pH, titratable acidity, ratio of soluble solids to acidity, sugars, total phenolics content, and antioxidant activity) using multivariate methods. Principal component analysis has revealed, that the chemical parameters, such as titratable acidity, ratio of soluble solids to acidity, and pH (PC1) and sugars and total soluble solids (PC2) appears to be the parameters most differentiating the samples. Five classes of juices with similar chemical composition were detected using hierarchical cluster analysis. The exploratory analysis of the overall chemical profiles revealed that the juices clear from concentrate, cloudy not from concentrate and freshly squeezed, were easily distinguishable due to their unique properties. In contrast, cloudy juices from concentrate showed properties similar to juices of other classes. The classification based on k-nearest neighbors method had high sensitivity and low classification error for clear juices from concentrate and cloudy not from concentrate. The classification failed for the cloudy juices from concentrate.