Lycopene and Beta-Carotene as Colorful and Versatile Tools to Illustrate Chromatography, Colorimetry, Alkene-Reactions and Health-Benefits

Abstract

Tomatoes are one of the main sources of carotenoids in the human diet, being responsible for important health-promoting benefits. Nowadays, a growing interest in making chemistry more environmentally friendly has been replacing some dangerous chemicals with daily-life materials. Accordingly, a greener protocol to teach chromatography, colorimetry, solubility, and some alkene reactions using tomato paste was developed. An innovative method was developed to efficiently extract the major tomato pigments, lycopene and carotenes, using accessible and low-toxicity organic solvents in the presence of a biodegradable dehydrating agent. Paper chromatography, using an eco-friendly eluent, allowed an easy and reliable separation of lycopene from the other carotenes, emerging as a simple and efficient technique for its detection. Then, a simple protocol enabled selective separation of the yellow carotenoids, cis-lycopene and (all)trans-lycopene by a “supermarket” column chromatography on potato starch eluted in a reversed-phase mode with low-toxicity eluents. Finally, reactions of carotenoids with common electrophiles were performed and easily monitored by the naked-eye through color alterations, demonstrating not only the presence of double bonds but also the principles of colorimetry and the mechanisms underlaying their health-promoting properties. Thus, a colorful, simple, sustainable, affordable, and extremely appealing activity was developed that is useful to illustrate the principles of solubility, solid–liquid extraction, chromatography, colorimetry, and addition reactions to double bonds, which may be implemented in first year practical classes of chemistry and biochemistry degrees. Moreover, this activity is well suited to motivate students’ learning through connections with daily-life chemistry, bringing chemistry closer to the real world.