Characterization and antimicrobial effect of starch-based edible coating suspensions

Starch is an edible polymer which may be used in combination with antimicrobial agents as thin coatings to extend shelf life of foods. This work was aimed to design and characterize an oleic acid nanoemulsion (OAN), as part of starch-based edible coating (EC) suspensions, incorporated with a mixture of three natural antimicrobials: lactic acid (ALA), nisin (NIS), and lauric arginate (LAE). OANs contained finely dispersed hydrophobic particles of 95.9 +/- 4.8 nm providing a stable suspension, and high optical clarity (27843.6 +/- 230.2 Transmittance units/nm). The EC suspension was prepared using waxy, acetylated cross linked, or oxidized starches (4% w/v) mixed with sorbitol (0.8 g/g starch), to which the nanoemulsion was added, and physicochemically characterized. The zeta potential of the OAN showed a large value (-35.08 +/- 1.26 mV). Despite EC suspensions showed low zeta potential values, no particles aggregation was observed after 4 months storage. The wettability coefficient (Ws) of EC suspensions was tested on three model foods, where those of waxy and oxidized starches gave Ws = -0.01 +/- 0.0 mN/m for fresh pork meat, with contact angle of 0 degrees. The EC suspension from waxy starch was tested to inhibit Brochothrix thermosphacta, Listeria monocytogenes Scott A and Micrococcus luteus ATCC 11509, alone, and in mixture. From a mixture design of experiments the optimum combination of antimicrobial agents was 3.75 mu g/mL NIS, 0.0625 mg/mL LAE, and 17.5 mg/mL ALA, which incorporated into EC suspensions produced similar antimicrobial effect. The properties of active EC suspensions may be used as coatings to extend the shelf life of fresh foods. (C) 2015 Elsevier Ltd. All rights reserved.