Antimicrobial and antioxidant activities of edible coatings enriched with natural plant extracts: In vitro and in vivo studies

Abstract

Consumers demand less use of chemicals on minimally processed fruits and vegetables so more attention has been paid to the search for naturally occurring substances able to act as alternative antimicrobials and antioxidants. The susceptibility of the native microflora of butternut squash and Listeria monocytogenes was analyzed by in vitro assays using (a) film-forming solutions (chitosan, carboxymethyl cellulose and casein), (b) oleoresins (olive, rosemary, onion, capsicum, cranberry, garlic, oreganum and oreganum + carvacrol 5%) and (c) film-forming solutions enriched with oleoresins. Film-forming solutions did not show significant antimicrobial properties. The oleoresins with meaningful antimicrobial activity against both squash native microflora and L. monocytogenes were olive and rosemary. In general, film-solutions containing 1% of different oleoresins showed limited antimicrobial effects against these indicator microorganisms. In vitro antioxidant properties were measured on different crude vegetable extracts. The enzyme source proved to affect peroxidase (POD) and polyphenoloxidase (PPO) susceptibility to the film-forming solutions. Most oleoresins significantly affected POD activity, regardless of the enzyme source. When the film-forming solutions were enriched with oleoresins, the latter lost, or retained their potential to reduce POD and PPO activities. In vivo experiments were focused on the treatments offering potential antibacterial and antioxidant benefits. The use of chitosan coatings enriched with rosemary and olive oleoresins applied to butternut squash did not produce a significant antimicrobial effect, however antioxidant effects were observed during the first day, exerting POD inhibition for up to 5 d of storage. Both oleoresins and chitosan enriched with them exerted significant antioxidant activities over PPO throughout 5 d of storage. The use of chitosan enriched with rosemary and olive did not introduce deleterious effects on the sensorial acceptability of squash. Chitosan enriched with rosemary and olive improved the antioxidant protection of the minimally processed squash offering a great advantage in the prevention of browning reactions which typically result in quality loss in fruits and vegetables.