Impact of Free Fatty Acids and Phospholipids on Reverse Micelles Formation and Lipid Oxidation in Bulk Oil

Abstract

Association colloids such as phospholipid reverse micelles could increase the rate of lipid oxidation in bulk oils. In addition to phospholipids, other surface active minor components in commercial oils such as free fatty acids may impact lipid oxidation rates and the physical properties of reverse micelles. In this study, the effects of free fatty acids on changes in the critical micelle concentration (CMC) of 1,2‐Dioleoyl‐sn‐glycero‐3‐phosphocholine (DOPC) in stripped corn oil (SCO) were determined by using the 7,7,8,8‐tetracyanoquinodimethane solubilization technique. Different free fatty acids including myristoleic, oleic, elaidic, linoleic and eicosenoic were added at 0.5 % by wt along with the DOPC into the bulk oils. There was no significant effect of free fatty acids with different chain length, configuration and number of double bonds on the CMC value for DOPC in bulk oil. However, increasing concentrations of oleic acid (0.5 to 5 % by wt) caused the CMC value for DOPC in bulk oils to increase from 400 to 1,000 μmol/kg oil. Physical properties of DOPC reverse micelles in the presence of free fatty acids in bulk oils were also investigated by the small angle X‐ray scattering technique. Results showed that free fatty acids could impact on the reverse micelle structure of DOPC in bulk oils. Moreover, free fatty acid decreased pH inside reverse micelle as confirmed by the NMR studies. The oxidation studies done by monitoring the lipid hydroperoxide and hexanal formation revealed that free fatty acids exhibited pro‐oxidative activity in the presence and absence of DOPC. Different types of free fatty acids had similar pro‐oxidative activity in bulk oil.

An “Omics” Approach for Lipid Oxidation in Foods: The Case of Free Fatty Acids in Bulk Purified Olive Oil

“…The results obtained from the TCNQ solubilization technique confirmed that the formation of reversed micelles did not occur when adding FFA to the purified oil in the range 0-30 mg g À1 : the absorbance at 480 nm remained near zero in the range of concentrations. This confirmed the conclusion of Kittipongpittaya et al, [27] who used the same analytical technique and smallangle X-ray scattering (SAXS). Table 1 reports the results of the regression analysis of the data regarding all the analytical indices considered in the present study as a function of time and FFA content.…”

“…They proposed that also in bulk oils, oxidation occurs within association colloids, at the interface of reversed micelles, where surface active compounds exert their activity. Kittipongpittaya et al evaluated the ability of FFA to form reversed micelles in bulk oils and concluded that their role in bulk oil oxidation was independent from reversed micelles formation. Xu et al studied, instead, the interaction of free fatty acids with oxidation of sterols and observed a time‐dependent effect of FFA, that induced an early acceleration of sterol degradation and subsequently either weakened their effect or inhibited the sterol oxidation.…”

Phospholipids in foods: prooxidants or antioxidants?

“…Recently, evidence of reverse micelles formed by phospholipids in oils stripped of their polar compounds was observed by means of small-angle X-ray scattering. 68,69 Reverse micelles can act as nano-reactors that can alter chemical reaction rates by bringing hydrophilic and lipophilic compounds into close contact, allowing increased interactions. 70 Kasaikina and co-workers 71 -75 used different surfactants in non-aqueous media, including bulk oil, as a simple self-assembling model to investigate the impact of physical structures on lipid oxidation.…”

Effects of α-tocopherol on the oxidative stability and incorporation of deuterium in volatiles from a linoleic acid-deuterium model system

“…Moisture in bulk oil plays important roles in the rates of lipid oxidation through forming association colloids with amphiphilic compounds including free fatty acids, monoacylgylcerols, diacylglycerols, and phospholipids (1)(2)(3). Bulk oils possess about 200-800 ppm moisture content although the water activity of bulk oils is reported to be 0 (1,(3)(4)(5). Reverse micelles are typical structures of association colloids in bulk oils and amphiphilic compounds that, like phospholipids, can form reverse micelles with moisture in oils (5).…”

“…Bulk oils possess about 200-800 ppm moisture content although the water activity of bulk oils is reported to be 0 (1,(3)(4)(5). Reverse micelles are typical structures of association colloids in bulk oils and amphiphilic compounds that, like phospholipids, can form reverse micelles with moisture in oils (5).…”