Abstract
In this study, the effects of an agro-industrial residue with active properties, pomegranate peel extract (PPE), were evaluated on the rheological properties of potential coatings based on chitosan (C) and gelatin (G). For this, rheological properties of the polymeric solutions were investigated in relation to PPE concentration (2 or 4 mg PPE g−1 solution), and to its incorporation order into the system (in C or in CG mixture). All solutions were more viscous than elastic (G″ > G′), and the change in PPE concentration had a greater influence accentuating the viscous character of the samples in which PPE was added to the CG mixture (CGPPE2 and CGPPE4). PPE addition to the CG mixture increased the angular frequency at the moduli crossover, indicating the formation of a more resistant polymeric network. This tendency was also observed in flow results, in which PPE addition decreased the pseudoplastic behavior of the solutions, due to a greater cross-linking between the polymers and the phenolic compounds. In general, all the studied solutions showed viscosities suitable for the proposed application, and it was possible to state the importance of standardizing the addition order of the components during the preparation of a coating.
Highlights
Its total phenolic content (TPC), determined by the Folin–Ciocalteu method, was 213 ± 6 mg gallic acid equivalent (GAE) g−1 extract. This result is consistent with that found by Derakshan et al (2018), who analyzed the TPC of extracts from the peel and the seed of three different types of pomegranates, finding a range of 276–413 mg EAG g−1 for the peel extracts [19]
It is worth mentioning that the variations observed in the TPC of different phenolic extracts are related to the most diverse factors: from intrinsic ones, such as the origin of the fruit and its harvest time, to extrinsic factors, such as the method of extraction adopted, the time of extraction, and the solvents used
The effects of pomegranate peel extract (PPE) concentration were more accentuated when it was added to the CG mixture, indicating that the other addition order evaluated may have led to a possible saturation of chitosan binding sites, making it difficult for this polysaccharide to form a polymeric network with the subsequent incorporation of gelatin
Summary
The search for edible food coatings that are biodegradable, non-toxic, and that have active properties has been increasing in recent years, aiming to extend the shelf life of foods while preserving their sensory characteristics and improving consumer safety [1,2]. There is an increasing number of studies that evaluate the most diverse polymers, natural or synthetic, and their physical-chemical, structural, and active properties in foods. In these studies, polysaccharides stand out as one of the groups of polymers that are most applied for coating purposes, due to their attractive properties of brightness, transparency, flexibility, barrier to the passage of water and gases, antimicrobial activity, among others [3]
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