DOI
https://doi.org/10.1021/acs.jchemed.8b01009

Summary
The paper presents the development of a laboratory experiment to introduce students to waste valorization. This is the process of reusing, recycling, or composting from wastes in order to produce useful products, or sources of energy. In this laboratory experiment (constituted of two sessions), waste valorization is demonstrated through transforming waste orange peel (WOP) into a marmalade-type gel by extracting a pectin-based mixture (or sol) and forming a gel in combination with an acidified sugar solution.
In the first session of a laboratory experiment, students working in groups can perform an aqueous extraction in acidic conditions to form a pectin-based mixture in the form of a sol from the WOP. Hot distilled water and ethanol are used to enhance the purity of the isolated pectin by facilitating the removal of ethanol-solvent components, including sugars, and inactivating enzymes without leaching soluble pectin fractions. In the second session, students can examine the rheological properties through rotational viscometry. Ethanol also serves to precipitate the pectin to form a sol, presenting an opportunity to study its rheological properties through capillary viscometry, a subject that has been identified as a troubling threshold concept within the biochemistry curriculum. Following the experiment, students presented their work as part of an oral presentation in their groups for 5 min each.
Beyond providing instructors with a green alternative to traditional borax-cross-linked PVA, this experiment allows students to utilize waste in a productive fashion to create and characterize a useful product that is familiar to them. In doing so, students can adopt a systems-thinking approach in the context of the life cycle of WOP. Therefore, through such a systems-thinking approach, by highlighting the interdependence of components, students can be challenged to apply scientific principles to solve real-world problems with due consideration of ethics and demonstrate the essential role that green chemistry has to play in finding solutions to global challenges.

Relevance for Complex Systems Knowledge
The paper deals with interdisciplinarity, systems thinking, and sustainable development.
The proposed experiment was designed to be interdisciplinary, allowing multiple departments (such as chemistry and physics) to collaborate in order to facilitate the session. It enables students to see how to achieve whole-systems-thinking “closed-loop” manufacturing of food products with all input materials fully utilized. Moreover, instructors can align this resource with the UN Sustainable Development Goals, specifically Goal 12, which aims to reduce the environmental impact of wastes through better utilization and management within the context of circular economy principles.

Point of Strength
The main strength of the publication is the suggestion of how a consideration of an entire system, as the life cycle of WOP, can assist learners to make a transition from a fragmented and reductionist knowledge of content to a more integrated and lateral understanding of this area.