Authors Clara R, Antonio A V, Jose A T, and Candida M
Research on edible coatings and films has been intense in recent years. Attempts to diminish crop losses and maintain the quality of fresh fruit for a longer period is a priority for all the producers. This is true both for fruit being directly sold to the consumer and for further processing. The development of coatings from polysaccharides has brought an increase in new types of coatings for extending the shelf-life of fruit and vegetables because of the selective permeabilities of these polymers to O2 and CO2. Polysaccharide based coatings can be used to modify the internal atmosphere of the fruit and thus retard senescence. Even though some edible coatings have been successfully applied to fresh products, other applications adversely affect quality. Modification of the internal atmosphere using edible coatings can increase disorders associated with high CO2 or low O2 concentrations. Therefore, it is only natural that the control of gas permeability of the films should be a priority in their development. The effectiveness of edible coatings for protection of fruit and vegetables depends primarily on controlling the wettability of the coating solutions, which affects the coating thickness of the film. Edible coating formulations must wet and spread uniformly on the fruit’s surface and, upon drying, a coating that has adequate adhesion, cohesion, and durability to function properly must be formed. Among other functionalities, edible coatings can act as carriers for food additives such as antioxidants and antimicrobial agents onto the surface of the food. The aim of this work was to study the ability of starch, carrageenan, and chitosan-based coatings to extend the shelf-life of strawberry fruit. This study was divided into two parts: in the first part coating composition was optimized and O2 permeability of coating solutions was determined; in the second, the coatings were applied to the strawberries, both in the laboratory and in the field, and the changes in the quality parameters were followed during storage of the coated fruit. The ability of polysaccharide-based (starch, carrageenan, and chitosan) coatings to extend the shelf-life of strawberry fruit (Fragaria ananassa) were studied, mainly for industrial applications. The coatings and strawberries were characterized in terms of their physical properties (superficial properties, wettability, oxygen permeability) to optimize coating composition. The optimized coatings were then applied to the fruit both in the laboratory and in the field and their effects on relevant quality parameters assessed. The superficial tension of the strawberry was 28.94 mN/m, and its polar and dispersive components were 5.95 and 22.99 mN/m, respectively. The critical superficial tension of the strawberry, obtained from a Zisman plot, was 18.84 mN/m. For each polysaccharide-based coating the best wettability was obtained for compositions: 2% starch and 2% sorbitol; 0.3% carrageenan, 0.75% glycerol and 0.02% Tween 80; 1% chitosan and 0.1% Tween 80. The oxygen permeability of carrageenan films was approximately 40% of that obtained with starch films. The addition of calcium to the starch film-forming solution produced an increase in the film thickness; nevertheless, no significant differences in oxygen permeability were obtained between films with and without calcium. The effects of application of these coatings to fresh strawberries were assessed by determining color change, firmness, weight loss, soluble solids, and microbiological growth over 6 days. No significant colour differences were found, and the minimum firmness loss was obtained in strawberries coated with carrageenan and calcium chloride. The minimum loss of mass was obtained for fruit with chitosan and carrageenan coatings both with calcium chloride. The addition of 1% di-hydrated calcium chloride to the coatings reduced the microbial growth rate on the fruit. The minimum rate of microbial growth was obtained for strawberries coated with chitosan and calcium chloride. The industrial application of calcium-enriched carrageenan coating on fresh strawberries resulted in a decrease in firmness loss when compared to non-coated fruit.
