Coencapsulação por spray drying de antocianinas extraídas de cascas de uva (Vitis vinifera var. Syrah) e α-tocoferol: caracterização e estabilidade

Abstract

The present study sought to characterize the microparticles obtained from the co-encapsulation of anthocyanins extracted from grape skins (Vitis vinifera var. Syrah) and α-tocopherol via spray drying. Briefly, grape skin extract was homogenized with gum arabic (20%), Tween 80 (0.2%), and different concentrations of α-tocopherol (0-control, 0.5, 1.0, 1.5, and 2.0%, w/w) relative to the total emulsion. Anthocyanin content, antioxidant activity, total phenolic content, α-tocopherol concentration, color, hygroscopicity, morphology, and the Fourier transform infrared spectroscopy (FTIR) results of each treatment were analyzed. The highest concentration of α-tocopherol led to the highest total phenolic content (8.69 mg gallic acid equivalent/g powder dry basis) and the lowest hygroscopicity (21.21 g adsorbed moisture/100 g powder dry basis) and anthocyanin content (0.917 mg malvidin-3-glucoside equivalent/g powder dry basis). Intermediate concentrations of α-tocopherol resulted in an increased incidence of microparticles with smooth surface and elevated antioxidant activity. The FTIR spectra verified the efficacy of the process, showing characteristic bands of the co-encapsulated compounds (at 1600 cm-1, which is related to the hydrogen bonds of the OH groups in grape carbohydrates, and at 1210 cm-1, which is related to the aromatic ether present in the structure of α-tocopherol). Overall, α-tocopherol concentrations between 1.5% and 2.0% (w/w) led to good powder properties (lower hygroscopicity, higher total phenolic content and antioxidant activity). The stability of the particles with zero (control), 1.0 and 2.0% (w/w) of α-tocopherol was also evaluated with respect to three main external factors (humidity, temperature, and light) via three different storage conditions: in an environment with relative humidity (RH) of 75% (20 °C, in the dark) for 47 days; a temperature of 60 °C (RH = 65%, in the dark) for 112 days; and with exposure to light (25 °C, RH = 70%) for 105 days. Moreover, the antioxidant activity, anthocyanin content, total phenolic content, and color parameters of these particles were assessed over time. The content of α-tocopherol and the FTIR spectra of the samples were determined at the initial and final times. A synergistic effect between compounds was observed under thermostability and photostability for color properties, content, and half-life time of anthocyanins. In contrast, an antagonistic effect was observed for the same properties when the particles were stored in an environment with RH of 75%. Greater reduction in α-tocopherol content was observed under thermostability and storage at 75% RH. Under thermostability and photostability, FTIR spectra exhibited decreased bands present at 2900 cm−1 (axial deformation of C–H) and 1210 cm−1 (aryl–O–C) in the α-tocopherol added treatments, and bands in the region between 1600 and 900 cm−1 (stretching of C–O–C and O–H) in all treatments. During storage of particles at 75% RH, slightly distorted FTIR spectra with higher absorption bands were observed. Based on these results, it was observed that α-tocopherol provided better stability to anthocyanins, as long as the particles are subjected to oxygen and humidity protection, which represents a potential contribution for the food sector.