Seeds of pomegranate, tomato and grapes: An underestimated source of natural bioactive molecules and antioxidants from agri-food by-products

Pomegranate, tomato and grape seeds are quantitatively relevant agri-food by-products rich in molecules beneficial to human health. To valorize this resource, the composition and antioxidant activity of seeds and deriving supercritical CO2 (SC-CO2) extracted oleoresins were evaluated. Grape seeds showed the highest content of total phenolic compounds (33.9 mg GAE/g), flavonoids (15.6 mg CE/g) and condensed tannins (14.0 mg CE/g), while tomato seeds presented the highest content of tocochromanols (159.6 μg/g). Grape seeds showed the highest total antioxidant activity (178.2 μmol TE/g), as evaluated by TEAC assay, followed by pomegranate (19.8 μmol TE/g) and tomato (9.8 μmol TE/g). Oleoresin yields obtained by SC-CO2 extraction from the seeds ranged between 3.1 (pomegranate) to 7.8 (tomato) g oleoresin/100 g. Total tocochromanols were abundant in pomegranate (2008 μg/g) and tomato (1769 μg/g) oleoresins; a relatively low amount was instead detected in the oleoresin extracted from grape seeds (636 μg/g). Carotenoids were not detected in all oleoresins. Pomegranate oleoresin had a higher antioxidant activity than the others. Mono- and polyunsaturated fatty acids were more abundant than saturated in all oleoresins, with the highest percentage of unsaturated fatty acids detected in pomegranate seed oleoresin (∼90%), mainly due to punicic acid (∼70%).