Effect of technological processing upon the antioxidant capacity of aromatic and medicinal plant infusions: From harvest to packaging

Antioxidants are secondary metabolites in plants, designed to protect them from abiotic stress; however, they may also improve one's general health, following regular ingestion. Since most foods from plant origin are consumed only after processing and formulation, the final activity exhibited by their antioxidants may be rather different from that in the original plant.Ten plants empirically used in Portugal in traditional medicine were accordingly studied - agrimony (Agrimonia eupatoria), eucalyptus (Eucalyptus globulus), walnut-tree (Juglans regia), myrtle (Myrtus communis), raspberry (Rubus idaeus), sage (Salvia sp.), savory (Satureja montana), sweet-amber (Hypericum androsaemum), thyme (Thymus vulgaris) and yarrow (Achillea millefolium), for total antioxidant capacity and total phenolic content. Significant variations were found between fresh and frozen forms: most plants decreased those features by 30-80 %. However, weather conditions prevailing during plant growth also had a significant impact, besides postharvest storage conditions - especially in the case of antioxidant capacity. Typically, a decrease occurred throughout processing and storage, which was maximum for myrtle and minimum for yarrow.The results of this research are useful in attempts to preserve the antioxidant content of plant-derived foods, or of plant additives in foods, via rational manipulation of processing conditions after harvest and throughout storage.

► Bioavailability of antioxidants in plant-derived foods depends on postharvest processing. ► Ten traditional plants in Iberian Peninsula were characterized for total antioxidant activity and phenolic content. ► Decay by 30-80% occurred during processing, being maximum for myrtle and minimum for yarrow. ► Data are useful for rational manipulation of processing conditions aimed at optimum antioxidant performance.