Free and esterified 4,4 '-dimethylsterols in hazelnut oil and their retention during refining processes

Free and esterified forms of sterols provide detailed information on the identity and the quality of vegetable oils. In this study, 4,4'-dimethylsterols in free and esterified forms were investigated in hazelnut and virgin olive oils. Moreover, a sample of solvent-extracted hazelnut oil was refined at the laboratory to monitor the effects of processing on the levels of 4,4'-dimethylsterols. Generally, the level of total 4,4'-dimethyslterols was higher in the esterified form (49-68%) compared with that in free form (32-51%) of these compounds in the hazelnut oil. In virgin olive oil samples, cycloartenol and 24-methylenecycloartanol were present in higher amounts in free forms (70-80%) than in esterified forms (20-30%). Among the refining processes, degumming, deodorization, neutralization and bleaching, only neutralization and bleaching considerably reduced 4,4'-dimethylsterols. In fully refined hazelnut oil, 18 and 37% of lupeol and an unknown compound X in the esterified form were lost, respectively. The loss of these two compounds in the free form was considerably higher, 26 and 72%, respectively. GC-MS analysis showed that adulteration of olive oil with a sample of fully refined hazelnut oil could be detected at a level as low as 2% by tracing lupeol in total or only in esterified forms of 4,4'-dimethylsterols. Further studies on the levels of free and esterified 4,4'-dimethylsterols and their retention during refining processes are anticipated in hazelnut cultivars from different origins.