From Agricultural Waste to a Powerful Antioxidant: Hydroxytyrosol as a Sustainable Model Substance for Understanding Antioxidant Capacity

Abstract

Students encounter antioxidants in many areas of their daily life. Antioxidants play a crucial role in cosmetics, in nutritional or dietary supplements, as additives for the preservation of food, and as a natural component in fruit and vegetables. Accordingly, antioxidants are believed to promote health through the prevention of oxidative stress by scavenging free radicals. The underlying oxidation and reduction processes of antioxidants are a central topic of chemistry classes. Additionally, antioxidants can be linked to aspects of sustainability. In this paper, the model substance chosen to demonstrate these aspects of antioxidants is hydroxytyrosol. Hydroxytyrosol is a natural, highly effective antioxidant, which is produced, for example, in olive trees and can be found in high concentrations in olive mill wastewater, which is potentially hazardous to the environment. In the first experiment, WELL-plate experiments are used to show the principal properties of antioxidants, both as reducing agents and radical scavengers, for the example of hydroxytyrosol. The experiments are based on the oxygen radical absorbance capacity (ORAC) test, which is widely applied in the food industry. In a second experiment, the properties of antioxidants are demonstrated using alginate balls as reaction vessels to produce a luminous bubble tea. Furthermore, the school-student-friendly extraction of hydroxytyrosol is presented.