Untargeted Chemometrics Evaluation of the Effect of Juicing Technique on Phytochemical Profiles and Antioxidant Activities in Common Vegetables

This study used ultra-high-performance liquid chromatography combined with ion-trap time-of-flight mass spectrometry (UHPLC-QTOF-MS) and complementary metabolomics approaches to investigate the effects of three processing techniques (blending, high-speed centrifugal juicing, and low-speed juicing) on the phytochemical profiles and antioxidant activities of 19 vegetables, including kale and beets. UHPLC-QTOF-MS combined with chemometric sparse partial least-squares discriminant analysis and heat map approaches identified 85 different metabolites. Kaempferol, quercetin glycosides, and amino acid-attached betaxanthins were identified as potential markers that differentiate the processing techniques, with higher relative abundances in kale juices produced in a low-speed juicer, followed by beet juices produced in a high-speed centrifugal juicer. The antioxidant activities were significantly different in juices produced by the three processing techniques and in different vegetable varieties, with the green kale juice produced by the low-speed juicer having the highest level of total phenolics (1201.31 μg/g of gallic acid equivalents) and DPPH value (1235.53 μg/g of ascorbic acid equivalents).