Preparation, physical properties, and evaluation of antioxidant capacity of aqueous grape extract loaded in chitosan-TPP nanoparticles

Grape extract is reportedly rich in phenolic compounds that possess strong antioxidant activities. Encapsulation of such extracts in nanoparticles (NPs) is an effective way to preserve various food products. In the present study, grapes were first extracted, and the amount of total phenolic content and different types of phenolic acids was determined. The extracts at different chitosan/extract weight ratios (1:0.25, 1:0.5, 1:0.75, and 1:1) were then encapsulated in chitosan nanoparticles (NPs) using the ionic gelation method. The extract-loaded chitosan nanoparticles were characterized by their physicochemical properties using the dynamic light scattering (DLS) technique, chemical properties using Fourier-transform infrared (FTIR) spectroscopy, and X-ray powder diffraction technique (XRD), the morphological properties using scanning electron microscopy (SEM), and the antioxidant activity using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) test. The encapsulation efficiency (EE) and loading capacity (LC) were also assessed. Our findings showed that the free radical inhibition effect of NPs significantly increased with an increase in extract concentration. Chitosan NPs presented acceptable encapsulation efficiency and loading capacity (LC), and the encapsulation process enhanced the antioxidant activity of the free grape extracts. At the weight ratio of 1:0.5, the particle size and zeta potential of the NPs were 177.5 +/- 2.12 nm and 32.95 +/- 0.49 mV, respectively. FTIR and XRD analyses verified the credibility of the encapsulated grape extract in chitosan NPs. These NPs can be an efficient way to increase the shelf-life of food products.