1. CHEMISTRY 1000 Topics of Interest #8: Mango Medicine?

2. Mangoes are big business. Including all of the processed foods containing mango (canned fruit, fruit purees, chutneys, etc.), mangoes are the fruit with the fifth highest production in the world. Since many of the mangoes are skinned and pitted for use in the processed foods, that generates a large amount of waste skin and pits. Christine Engels, a researcher at the University of Alberta, recently published work demonstrating that a class of food preservatives called tannins can be extracted from mango pits that would otherwise just be dumped or burned. Mango Pits Contain Antibacterial Tannins C. Engels et al. Journal of Agricultural and Food Chemistry (2009) 57, 7712-7718.

3. Tannins are a class of polyphenols that occur in many plants. (A polyphenol is a benzene ring with more than one –OH attached.) Polyphenols are very good at acting as Lewis bases toward metal cations. Since coffee and tea contain significant amounts of polyphenols (including kinds of tannins), drinking them when eating foods rich in iron, zinc, etc. will inhibit uptake of those minerals unless there is an acid (usually lemon juice) in the tea/coffee: Mango Pits Contain Antibacterial Tannins C. Engels et al. Journal of Agricultural and Food Chemistry (2009) 57, 7712-7718.

4. This is not to say that tannins (and other polyphenols) don’t have good uses. Some of them can act as antioxidants. Mango Pits Contain Antibacterial Tannins C. Engels et al. Journal of Agricultural and Food Chemistry (2009) 57, 7712-7718. Also, because of their ability to bind to essential minerals, some tannins can inhibit growth of bacteria. In the research at the University of Alberta, it was clearly demonstrated that tannins extracted from the mango pits (sample structure at right) prevented growth of several different species of bacteria including Listeria monocytognes, a species known to have caused several food poisoning outbreaks.