Effects of essential oils released from active packaging on the antioxidant system and quality of lemons during cold storage and commercialization

The antimicrobial and antioxidant properties, among others, of plant essential oils (EOs) to preserve the quality of fruit and vegetables have been widely studied. Nevertheless, little is known about the antioxidant system response in fruit and vegetables, especially in citrus fruit, due to EOs treatments. The antioxidant systems (antioxidant enzymes, ascorbic/dehydroascorbic acids contents and phenolic compounds) of the flavedo tissue of lemons packaged under cardboard packages without (control) or with encapsulated EOs (active; carvacrol: eugenol mix (80:20) in beta-cyclodextrin) were hereby studied during cold storage (8 degrees C up to 35 d), with commercialization periods (22 degrees C for 5 d) after every 7 d of cold storage. The lemon quality (titratable acidity, pH, soluble solid content, external colour, firmness and microbial surface load) and nutritional/bioactive content of the lemon pulp (ascorbic/dehydroascorbic acid contents, total phenolic content and total antioxidant activity) were determined during cold storage and after commercialization periods. EOs released from the active pack-aging increased the activities of the antioxidant enzymes superoxide dismutase/ascorbate peroxidase, dehy-droascorbate reductase and catalase in the flavedo tissue with maximum values after commercialization periods (80, 20, 160 and 50% higher than control samples) corresponding to previous cold storage for 7, 14 and 21 d, respectively. These antioxidant responses were also reflected in the ascorbic/dehydroascorbic acid contents, total phenolic content and total antioxidant activity of the flavedo tissue. The active packaging highly controlled the microbial growth with 1.6-1.9 log units lower psychrophilic loads than control samples at the end of cold storage with also lower decay incidence after commercialization. The physicochemical quality, colour and firmness of lemons were not negatively affected by the active packaging. The nutritional/bioactive quality of the lemon pulp was increased after commercialization periods, particularly inducing EOs from the active packaging with higher total phenolic content increments (30-70%) than control samples (15-20%), while no ascorbic acid content differences were observed among active and control samples after commercialization. In conclusion, this study shows a detailed picture of the response of the antioxidant system in lemons due to the EOs released from the active packaging, with the antioxidant activity being increased while the quality of the lemons was not affected.