Enhanced antioxidant properties of tara (Caesalpinia spinosa) gallotannins by thermal hydrolysis and its synergistic effects with α-tocopherol, ascorbyl palmitate, and citric acid on sacha inchi (Plukenetia volubilis) oil

The antioxidant potential of thermally hydrolyzed tara pod extracts (HTEs) at 121 °C, 103 kPa for different time were tested against sacha inchi oil (SIO) oxidation. The antioxidant efficacy on SIO of 200–400 ppm HTE for 180 min were compared to α-tocopherol (α-T), citric acid (CA) and ascorbyl palmitate (AP). Additionally, synergistic or antagonistic effects in binary mixtures of HTE with α-T or CA or AP were tested. Accelerated storage tests (55 °C for 30 days) were used to evaluate peroxide (PV), p-anisidine values (p-AV) and stability of naturally occurring SIO tocopherols and phytosterols. Antioxidant capacity (AC) and the antioxidant efficacy on SIO significantly increased as the HTE hydrolysis degree (HD) increased. The mixture of 400 ppm HTE and 100 ppm AP displayed a synergistic effect and reduced the rate of peroxide formation, p-AV and better protected SIO tocopherols. HTEs protect oils due to their high AC being an interesting alternative as natural antioxidant. Practical applications: Tara pods are an important source of gallotannins with antioxidant and antimicrobial properties widely used by the pharmaceutical, chemical, painting, and tannery industries. The partial thermal hydrolysis of gallotannins results in an increment of antioxidant activity determined in vitro by the ABTS, FRAP, and ORAC assays and to increase the efficacy against oxidation of sacha inchi oil (a food matrix rich in polyunsaturated fatty acids). These results demonstrate that partially hydrolyzed gallotannins with a high antioxidant activity are an important alternative for the functional and nutraceutical industries.