Isolation of ursolic acid from apple peels by high speed counter-current chromatography

Cuticular waxes of four varieties of Malus domestica were investigated regarding their content of ursolic acid. Peels from Fuji, Gala, Smith and Granny Smith apples were extracted with chloroform, ethyl acetate and/or ethanol. The crude extracts were purified by high speed counter-current chromatography (HSCCC), by using mobile and stationary phases derived from the two-phase solvent system composed by n-hexane:ethyl acetate:methanol:water in the proportion of 10:5:2.5:1. The phase proportions and the relative distribution of ursolic acid between the two-phases were optimized by TLC and optical densitometry, by comparison with an authentic sample of ursolic acid. The amount of ursolic acid present in the extracts as well as the characterization of the isolated compound were made by high resolution gas chromatography coupled to mass spectrometry (GC–MS), 13C nuclear magnetic resonance (13C NMR), Infrared; and by comparing thin layer chromatography and flame ionization detection gas chromatography (GC–FID) patterns with the commercial sample. The average content of ursolic acid of 0.8 mg/cm2 in the peel (around 50 mg per medium sized fruit with a surface area of 50–70 cm2) was found in the Fuji and Smith varieties, whereas 0.5 mg/cm2 and 0.2 mg/cm2 were the amounts calculated for Granny Smith and Gala, respectively. The HSCCC technique was shown to be a good method to purify free ursolic acid from apple peels and could represent a new technological tool to be developed to exploit industrially this source of product.