Efficient and Simple Extraction Protocol for Triterpenic Acids from Apples

Triterpenic acids (TA), a class of triterpenoids, are widely distributed as secondary metabolites in plants. They have a pentacyclic structure and show high structural diversity. In this work, a simple but efficient method for extraction and detection of TA derivatives from apple peels is described. The method is technically straightforward and robust and can be implemented in both undergraduate laboratories and science classes or projects in school: Apple peels are (i) extracted with ethyl acetate, (ii) degreased with cyclohexane, and (iii) reconstituted in ethanol. Yields of about 2.1 g of extract/100 g of dry weight apple peel were obtained, which consisted of >70% TA (56% ursolic acid (UA), 10% oleanolic acid (OA)). The TA pattern can be evaluated by thin layer chromatography (TLC) using simple detection with a KMnO₄ solution. The separation of the different TA derivatives on normal phase TLC plates enables learning how the chemical structure affects the chromatographic separation. The whole procedure requires 3–4 h without the drying steps. The TA extraction represents suitable content for student education since they learn and discuss natural products and secondary plant metabolites. The performance of an extraction, purification of natural products, and observation of chromatographic separation and detection are also learned in this method. Using this simple procedure, up to 1 g/100 g of dry weight UA can be generated from apple peels. While only apple peel is used for the experiment, the rest of the apple fruit was eaten by the students. Thus, the experiment itself is a demonstration of how side streams of food production can be used as a source for chemical compounds.