One of the most common reactions that play a key role in frying oil degradation is hydrolysis. The linear increase of the free fatty acid content in frying media, regardless of frying temperature,was observed in all frying experiments (Fig. 2a). The most relevant changes in the free fatty acid content were observed in palm oil used for frying at the highest temperature (180 C). According to the Polish Directive from the Minister of Health from 25 September 2012 (Dziennik Ustaw, 2012), the acceptable level of free fatty acids in a frying medium cannot be higher than 2.5 mg KOH g of fat. This level was not exceeded by any of the samples in our experiment. Other authors have provided supporting evidence for good hydrolytic stability of palm oil