Analysis of free and esterified sterols in vegetable oils

Abstract

sterols were separated by silica gel column chromatography upon elution with n-hexane/ethyl acetate (90:10 vol/vol) followed by n-hexane/diethyl ether/ethanol (25:25:50 by vol). Both fractions were saponified separately and the phytosterol content was quantified by GC. The analytical method for the analysis of esterified and free sterols had a relative standard deviation of 1.16% and an accuracy of 93.6-94.1%, which was comparable to the reference method for the total sterol analysis. A large variation in the content and distribution of the sterol fraction between different vegetable oils can be observed. Corn and rapeseed oils were very rich in phytosterols, which mainly occurred as steryl esters (56-60%), whereas the majority of the other vegetable oils (soybean, sunflower, palm oil, etc.) contained a much lower esterified sterol content (25-40%). No difference in the relative proportion of the individual sterols among crude and refined vegetable oils was observed.In vegetable oils, plant sterols mainly occur as free sterols or steryl esters of FA. The biosynthesis, biological function, and nutritional importance of phytosterols has recently been reviewed (1). The conventional method for sterol analysis involves a saponification of the TAG followed by an extraction of the unsaponifiable fraction with an organic solvent in order to determine the total sterol content (1). However, important information on the phytosterol fraction is lost through saponification. The steryl ester fraction is a complex mixture consisting of a variety of phytosterols esterified to various FA. The distribution of FA esterified to sterols differed considerably from the FA in the TAG of the vegetable oil. All steryl esters contained significantly higher levels of unsaturated FA compared to the corresponding TAG composition of the oil (2,3).Only a few literature reports are available on the combined quantification of free and esterified sterols. Methods reported so far have separated esterified and free sterols by either silica gel column chromatography, preparative TLC, or normalphase solid-phase extraction followed by saponification and GC quantification of both fractions (2-7). The esterified/free sterol content has been published for some vegetable oils (8).Some analytical methods have reported the quantification of steryl esters without saponification of the TAG. Steryl esters, sometimes in combination with free sterols, were isolated from TAG by TLC or normal-phase LC and quantified by GC or HPLC (3,(9)(10)(11)(12)(13). This direct analysis of the steryl ester fraction always resulted in an incomplete separation of the different steryl esters.In summary, few analytical reports deal with a separation of the esterified/free sterol fraction, and quantitative data on the free and esterified sterol content in vegetable oils are scarce. This study reports on the optimization and evaluation of an analytical method to determine the level of free and esterified sterols in vegetable oils followed by a quantification of the free and esterifie...

Effects of refining process on sunflower oil minor components: a review

“…Phytosterol content and composition changes during the hole refining process were evaluated by Verleyen, Forcades et al (2002) who found that the process modified the phytosterol composition by increasing the esterified sterols passing from 28.6% in bleached oil to 40% in the refined oil (after the deodorization) of the total sterol content. Karaali (1985) determined in chemically refined sunflower oil a decrease of 60.3% on total phytosterols, with the highest loss during the physical neutralization step.…”

“…A significant decline in the total sterol content in vegetable oil has been reported during the chemical neutralization step (Gutfinger and Letan, 1974), which is attributed to a liquid-liquid partitioning of phytosterols into the soapstock (Serani and Piacenti, 1992 (Alpaslan et al, 2001;Ergönül and Köseoǧlu, 2014;Karaali, 1985;Kreps et al, 2014;Nergiz and Çelikkale, 2011;Talal et al, 2013;Tasan and Demirci, 2005;Verleyen, Forcades et al, 2002).…”

Effects of a Total Dietary Fish Oil Replacement with Vegetable Oils to the Survival, Growth and Development of the Blue Swimming Crab Portunus Pelagicus Early Juveniles

“…Such a supplementation was more than sufficient to satisfy the requirements for S. serrata [21], which is an essential nutrient for crustaceans due to their inability to synthesize this de novo [29]. Another possible contributor to the reduced whole-body cholesterol was due the presence of phytosterols, which can diminish cholesterol absorption [30], and the tested vegetable oils in the current study are also known to contain this compound [31]. In addition, it may be possible that cholesterol transport via lipoproteins was disrupted as suggested by Noordin et al [2].…”

Phytosterol and its esters as novel food ingredients: A review

“…The most important sterol present in vegetable oils is -sitosterol, a desmethyl sterol, which accounts for 38 to 95% of the total phytosterols available in various oils (Verleyen et al, 2002) whereas mono and di-methyl sterols are found in lower amount in these oils (Johansson et al, 1979;Chryssafidis et al, 1992;Eldin and Appelqvist, 1994) but certain oils such as olive and linseed oil contain substantial amounts of dimethyl sterols (Johansson 1979). Distribution of phytosterols to free sterols and steryl fatty acid esters account for different proportion in different oils (Johansson et al, 1979;Ferrari et al, 1996;Verleyen et al, 2002;Phillips et al, 2002;Worthington and Hitchcock, 1984;Gordon and Griffith, 1992) for example-free sterols accounts for nearly 54-85% of total phytosterols in soybean, sesame, olive, cotton seed, coconut, safflower, and peanut oil whereas the proportion varies for 32-44% in canola, rapeseed, corn, avocado and sunflower oil (Phillips et al, 2002).…”