Wealth from by-products: an attempt to synthesize valuable gold nanoparticles from Brassica oleracea var. acephala cv. Galega stems

Abstract

In the last years, the growth of the world’s population has resulted in an increase in the demand for food. Vegetables and fruit are essential for human nutrition but, regrettably, half the fruit and vegetables produced worldwide are wasted. The food industry generates tons of by-products during processing, for instance, peels, seeds and stems, which still possess bioactive compounds that can be of interest for other applications. The Brassicaceae species includes some of the most consumed vegetables worldwide known for their antioxidant activity associated with the presence of phenolic compounds. In this study, the stems of Brassica oleracea var. acephala cv. Galega (hereafter BG) were employed to prepare an aqueous extract. Then, its antioxidant potential was evaluated by means of the in vitro analysis of its ability to scavenge the free radical 1,1-diphenyl-2-picryl-hydrazyl (DPPH), the quantification of the total phenolic content and the analysis of the reducing power. Furthermore, the stem aqueous extract was employed to produce gold nanoparticles (AuNPs), acting as a reducing and stabilizing agent. AuNPs were characterized by UV–Visible and Fourier transform infrared spectroscopy. The size and shape of the nanoparticles was analyzed by the acquisition of transmission electron microscopy images, confirming the formation of spherical AuNPs with mean diameters of 25.08 ± 3.73 nm. Finally, three antioxidant assays were performed in the extract after the synthesis of AuNPs. The synthesis of AuNPs employing BG stem extract was revealed to be a good alternative for the revalorization of Brassica by-products.