Perfil de liberação de óleos vegetais encapsulados em nanofibras de poli(ácido lático) para aplicação na piscicultura

Abstract

Nanofibers are polymeric structures that have the shape of threads and nanometric diameters. These materials has a high surface-to-volume ratio as their main feature. Many techniques can be used to its production, with solution blow spinning being an example of a simple technique with low cost. The encapsulation of active agents or nutrients in nanofibers can be useful to solve environmental problems, like the nutrition of farmed fish. One of the main difficulties faced in pisciculture is the high cost of the feed fortified with fish meal and fish oil. The use of these compounds enhances the content of fatty acids of the n-3 and n-6 series on the fishes, which contributes to their healthy development. However, this practice is economically and environmentally unsustainable, since these products are obtained from finite marine sources. Therefore, the aim of this project was the production of poly(lactic acid) nanofibers containing corn oil and linseed oil in different proportions. Posteriorly, nanofibers were characterized by Differential Scanning Calorimetry, Scanning Electron Microscopy, and Fourier-Transform Infrared spectroscopy The contact angle and encapsulation efficiency were also determined. A general feed formulation was produced and the release profile of the nutrients encapsulated in the nanofibers and free in the feed was studied and compared. The release tests were performed in vitro in environment simulating the tank water and the gastrointestinal conditions. The results showed that the encapsulation of the vegetable oils in the polylactic acid matrix was successful, since the infrared spectrum proved the interaction between the substances (characteristic vegetable oils peaks at 2925 and 2853 cm-1 were seen in the nanofibers spectra), and the encapsulation efficiency results were between 81.54±10.36% and 99.14±4.55%. The analysis of the thermal events showed the plasticizer effect of the vegetable oils because a small decrease in the glass transition of the polylactic acid was observed (from 63°C to 61°C); there was also a decrease in the cold crystallization temperature (from 93ºC to nearly 86ºC), indicating that the addition of oils would facilitate the crystallization process. Beyond that, the results of the contact angle allowed to affirm that all nanofibers are hydrophobic (all presented contact angles higher than 90°), which is important to protect the nutrients against release when in contact with the aqueous medium. The Scanning Electron Microscopy analysis showed that all nanofibers presented uniform morphology and smooth surface, with an average diameter between 157±49 nm and 385±133 nm. Through the comparison of the vegetable oils release from the nanofibers (encapsulated) and from the feed (free), it was possible to verify the importance of the nanofibers for this application since the polymeric matrix enhances the bioavailability of the nutrients.