Preliminary study of the effects of heating on virgin olive oil blended with mild deodorized olive oil.

It is known that virgin olive oil (VOO) has higher nutritional quality and health benefits – especially due to the presence of a wealth of phenolic compounds - in comparison to other vegetable oils. Unfortunately, it is also well known that a great number of olive oils fraudulently sold as VOOs are actually illegally mixed with other cheaper olive oils of lower quality and poorer characteristics. The so-called "mild deodorized" olive oils are nowadays the most used adulterants, because of their difficulty of being detected when in mixture with VOOs. These oils commonly show physico-chemical characteristics similar to genuine VOOs. In addition, the mild conditions illegally applied for their deacidification and deodorization do not lead to the formation of chemical markers that could be exploited as forensic proofs of the fraud. Microwave heating is commonly utilized for home cooking, food catering and industrial processes. Microwave heating was reported to induce significantly higher amount of compounds formed by oxidation and hydrolysis of lipids in comparison with traditional cooking treatments, probably as the result of a different extent of radical formation. In this preliminary study, mild deodorized olive oil and their mixtures with VOO have been analyzed after heating treatments by microwave and conventional oven. Different patterns in oxidative and hydrolytic degradation of lipids in genuine and sophisticated olive oils have been evaluated by chromatographic and spectroscopic methods and related to heating treatments. The experimental plan focused on the following points: a) analysis of 1,2 and 1,3-diglycerides and monoglycerides content by GC and 31P-NMR methods to assess the degree of hydrolysis; b) determination of oxidative status of the samples by volatile compounds (SPME/GC-MS) and accelerated aging test (OSI); c) study of the changes in the phenolic profile upon heating by HPLC-DAD/MS and 1H-NMR.