A novel approach to fabricate edible and heat sealable bio-based films from vegetable biomass rich in pectin

Abstract

Vegetable-based bioplastic materials, obtained from the upscaling of food byproducts showed a good potential for replacing plastics in single-use applications. This work presents a novel strategy for the improvement of the mechanical properties and water stability of materials derived from orange peel. Herein, the reinforcement of the structure involves the cross-linking between the carboxylic acid groups present in the pectin matrix and the calcium from two different salts: calcium chloride (CaCl2) and calcium carbonate (CaCO3) forming the well-known egg-box structure. Before adding the inorganic salts, the agro-food waste was hydrolyzed at pH 2 using citric acid to favor the availability of the inner compounds to interact. Then, the cross-linking of the pectin comprising the waste using Ca ions was studied with two different pH conditions, above and below the pKa of the pectin (3.5 pH). In general, films fabricated at pH 4.5 exhibited a higher degree of cross-linking with respect to the films processed at pH 2. This resulted because at pH 4.5 the carboxylic groups of pectin acquired a negative charge enhancing the interaction with calcium cations. Samples with CaCl2 displayed superior mechanical properties while CaCO3-loading films showed moisture resistance. Finally, we showed the potential of these materials, composed only of edible ingredients (orange peel, calcium salts, and citric acid), to be fabricated into heat sealable pouches or applied as coatings for food protection. The latter application leveraged the antioxidant properties of the orange peel, successfully reducing the browning effect of oxidation in apple slices.