Encapsulação de extrato da casca de cebola roxa (Allium cepa L.) em fibras ultrafinas de amidos de batata-doce pela técnica de electrospinning

Abstract

Red onion skin extract (ROSE) contains phenolic compounds that are sensitive to environmental conditions. For that, they must be protected for better preservation and maintenance. The objective of the study was to produce ultrafine fibers from native starch from two sweet potato cultivars (yellow and white) with different concentrations of ROSE (0, 3, 6, and 9%, w/w) encapsulated by electrospinning and non-encapsulated. The polymeric solutions for encapsulation of the ROSE were composed by 0.6 g of starch (20%, w/v) in 3 mL of formic acid (75%, v/v). The electrospinning parameters were: constant flow of 0.75 mL.h-1 ; voltage of 18 kV; and distance of 20 cm from the needle tip to the collector plate. The electrical conductivity and apparent viscosity of the polymeric solutions were evaluated. The phenolic profile of the ROSE was analyzed by high performance liquid chromatography. The ultrafine fibers were evaluated by morphology, size distribution, encapsulation efficiency, thermogravimetric analysis, simulation of the in vitro release of phenolic compounds under hydrophilic and hydrophobic conditions, contact angle, in vitro antioxidant activity against ABTS and DPPH radicals, and in vitro antibacterial activity against Escherichia coli and Staphylococcus aureus. The phenolic compounds identified in ROSE were quercetin 3-o-acetyl-rhamnoside, myricetin, quercetin 3-o-glycoside, isoramnetin 3-glucuronide, quercetin, and apigenin 7- arabinoside. Significant difference was found in the apparent viscosity and electrical conductivity of the polymeric solutions between the different starches. The ultrafine fibers presented distinct morphologies according to the ROSE concentration. However all fibers presented random morphologies, without the presence of beads, and average diameters ranging from 251 to 611 nm. The ultrafine fibers, when compared to the extract, withstand high temperatures until their degradation. The phenolic compounds identified in the encapsulated-ROSE showed low release of phenolic compounds under hydrophilic conditions and high release under hydrophobic conditions. The ultrafine fibers were more permeable (through the contact angle analysis, as the ROSE was incorporated. The antioxidant activity of the ROSE was 97,97 and 84,07% for the ABTS and DPPH radicals, respectively. The ultrafine fibers when encapsulated with 9% ROSE showed inhibition of the ABTS radical above 92%, close to the non-encapsulated ROSE. The antibacterial analysis showed inhibitory activity against E. coli and S. aureus for the encapsulated and non-encapsulated ROSE. However, only the non-encapsulated ROSE presented bactericidal activity. The ultrafine fibers showed to be promisor for application in the food industry, being necessary to determine the objective, conditions, characteristics, and purpose in the food matrix or packaging, and then choose an specific concentration of the ROSE into the ultrafine fibers for the effective application.