SUPRAMOLECULAR ORGANIZATION OF TRIGLYCERIDES IN EXTRA-VIRGIN OLIVE OILS AS ASSESSED BY NMR RELAXOMETRY

Abstract

Low resolution nuclear magnetic resonance (NMR) relaxometry revealed that triglycerides in extra-virgin olive oils are organized in inverse-micelle-like supramolecular structures held together by weak interactions such as van der Waals and hydrogen bonding. The formers can be established among the external apolar tails, while hydrogen bonds are present among the internal polar triglyceride heads, involving also the polar minor constituents of extra- virgin olive oils. The supramolecular assembly has been supported by experiments conducted by heating the samples in the NMR probe at four different temperatures. In addition all the oils were also added with increasing amounts of glacial acetic acid (AcOH). NMR relaxometry data at room temperature revealed that T1 values increased with the amount of the added AcOH. Moreover, it was noticed that when the volume of acetic acid was around 20 % of the sample volume, a separation between an oily layer and an acetic acid phase was achieved. The latter appeared to contain from 50 to 80 % of the total amount of the minor polar constituents of extra-virgin olive oils (i.e. polyphenols, chlorophylls, sterols, some terpenes and so on). Such findings were interpreted with a conformation re-arrangement of triglycerides from ordered supramolecular inversemicelle- like systems to micelle-like leading to formation of emulsions. Based on the results of the present study, it can be suggested that extra-virgin olive oils are not disordered and amorphous liquids but systems whose constituents are arranged in tidy supramolecular aggregates. The compartmental evidence of the minor polar extra-virgin olive oil components may pose new questions about their absorption pathways in the human nutrition.