Ergosterol as a marker for the use of degraded olives in the production of olive oil

The quality of olive oil depends, among other factors, on the quality of the olives used. Ergosterol is proposed as a marker for olives degraded by yeast or mold, since yeast as well as mold produce ergosterol, whereas olives do not. Ergosterol was determined in olive oil by on-line HPLC-GC-MS, using the high efficiency of HPLC to separate ergosterol from the sterols that are present at far higher concentrations. The detection limit was around 0.1 mg kg−1 oil. Among 50 extra virgin olive oils, 5 contained less than 0.1 mg kg−1 ergosterol, 18 were in the range 0.1–2 mg kg−1 and the highest concentration was 39 mg kg−1. Oil extracted from degraded olives contained ergosterol in a range of 21–289 mg kg−1, with higher values in the samples with a high number of yeast and mold cells. Being a marker for degraded olives, the ergosterol concentration should be related to fatty acid ethyl esters, formed by ethanol from fermentation by yeast, but the ergosterol concentration is considered more pertinent, since the ethyl esters only detect activity of yeast and their concentration depends on the conversion of the ethanol to fatty acid ethyl esters by transesterification in the olives.