The aim of the present study was to develop and characterize edible films produced from whey protein concentrate (WPC) and plasticized with different contents of glycerol (Gly) and/or trehalose (Tre) in order to evaluate new edible film formulations for their potential use in food packaging applications. Additionally, potential changes in the film mechanical properties during storage at ambient and freezing conditions were considered. Moisture content, solubility, thickness, transparency, microstructure, colour parameters, and mechanical properties were assessed. The films incorporated with Tre were more insoluble in water than WPC/Gly films, being more suitable for food applications. WPC/Gly and WPC/Tre films were clear enough to be used as see-through packaging. However, when Tre was included into WPC/Gly film formulations, film opacity increased. Scanning electron microscope (SEM) images suggested that this phenomenon may be related to the growth of Tre crystals in the film matrix. Moreover, when Tre concentration increased in the WPC/Gly matrix, film surface was more heterogeneous. Interestingly, the presence of Tre in WPC-based films was effective in preventing Maillard reaction after heating. WPC/Tre films were the most rigid but the least stable for storage, resulting more susceptible to rupture and cracking. Only WPC/Gly and WPC/Gly-Tre 8% films were rather flexible, manageable, and stable up to 90 days of storage under ambient and freezing conditions. These findings can be used to better design applications of edible films containing plasticizers that may crystallize over time in order to optimize film formulation in a rational manner towards their eventual application as food packaging.

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Potassium sorbate (PS) (0.5%, 1.0% and 1.5% w/w) was included into whey protein concentrate (WPC)/glycerol (Gly) edible films at pH 5.2 and 6.0. The films inhibited or retarded the growth of Shiga toxin producing Escherichia coli (STEC) pathogens in both diffusion and barrier tests. Bacterial growth inhibition was dependent on PS content at both pH values. PS release was not affected by pH. Scanning electron microscopy (SEM) was used to analyze the microstructure of the films and gain a better understanding of their optical parameters. Acidic control films (pH 5.2) prepared without PS were the least transparent. SEM micrographs confirmed the greater structural heterogeneity of these films, coinciding with opacity. The incorporation of PS into WPC/Gly films improved transparency and produced a smoother surface than acidic control ones. The utilization of active packaging based on whey proteins and organic acids to control and prevent the dissemination of STEC pathogens may be an effective, safe, ecological and relatively inexpensive alternative to be used in the food packaging industry.

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Summary Prefreezing application of whey protein concentrate (WPC)‐based edible coating to maintain quality attributes of strawberries was studied. Beeswax (BW) was added to the solutions (0%, 20% and 40% with respect to the solids contained in the mixture WPC/glycerol). Coated and control fruits were frozen, stored at −20 °C and thawed. After thawing, weight loss, firmness, microstructure and colour parameters were measured. Coating with 20% BW reduced strawberries weight loss after thawing (55%). Strawberries firmness was maintained equally in all groups analysed although a slight improvement at the cell microstructure alterations caused by the freezing process was observed in coated fruits. Strawberries brightness was similar in all groups. Colour parameter a* showed a tendency to decrease with the increasing BW concentration, and only b* of coated fruits was lower than controls. The application of whey protein coating could be an attractive treatment to maintain quality attributes of strawberries undergoing the freezing process.