Development of zein nanofibers for the controlled delivery of essential amino acids for fish nutrition
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Development of zein nanofibers for the controlled delivery of essential amino acids for fish nutrition Samanta Costa Machado Silva1 · Raphael Henrique Silva Fuzatto2 · Diego Alvarenga Botrel3 · Júlio Cesar Ugucioni4 · Juliano Elvis Oliveira2 Received: 7 April 2020 / Accepted: 1 October 2020 © Springer Nature Switzerland AG 2020
Abstract In the present paper, films and nanofibers of zein and zein/tryptophan were produced by casting and eletrospinning. The films and nanofibers were characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and controlled release and digestibility tests. In vitro releasing of tryptophan was evaluated using a spectrophotometer UV–Vis. Interactions between tryptophan and zein were confirmed by thermal (TGA) and spectral (FTIR) analyses. SEM micrographs provided evidence of a smooth and homogeneous structure for films and nanofibers without and with tryptophan. FTIR spectroscopy indicated seconddegree intermolecular interactions between amide groups of zein and tryptophan. X-ray analysis indicated the formation of crystals that did not interfere with the crystallization of amino acid. By in vitro release experiments, it was possible to observe that the tryptophan releasing follows nearly Korsmeyer–Peppas model for the nanofibers and Peppas–Sahlin model for films, indicating the releasing process of the nanofibers are by diffusion of the amino acid and, for films, by relaxion of polymeric chain. Finally, in vitro digestibility a considerable amount of tryptophan was observed, suggesting more access of fishes for tryptophan. Keywords Electrospinnig · Tryptophan · Controlled release · In vitro digestibility
1 Introduction Fish farming comprises a constantly expanding aquaculture sector in Brazil [1]. Aquaculture was the most prominent meat production sector between 2004 and 2014, with an average growth of 8%, against 4.1% for poultry farming, 5.1% for cattle raising and 2.9% for pig farming. Tilapia, the main grown aquaculture species in the country, presented an average production increase of 14.2% per year in the same period [2]. Its meat characteristics and the ease of animal breeding, are increasingly attracting the market. However, the technological package for tropical fishes commercial production still needs adjustments, such as
nutritional aspects of aquafeed [3]. Diets with insufficient protein levels can slow fish growth, compromise food efficiency, or mobilize protein from some tissues to maintain other vital functions [4]. Thereby, several studies [5, 6] search to develop more efficient systems for making essential amino acids available in the diet of tropical fishes. To meet the fish production in the country, considering the system of cultivation in cages and ponds, it is important that the animals receive a diet capable of meeting the required nutritional requirements. The essential amino acid tryptophan is present in the composition of feed used in the manufacture of fee
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