Free phytosterols

Extraction of free phytosterols and steryl conjugates In principle, sterols are extracted with common organic solvents like hexane, heptane, methanol, and chloroform, but the more polar conjugates (SFs, SGs, and ASGs) require more polar extraction solvents to be quantitatively extracted from plant sample materials. Therefore, if only selected class(s) of steryl conjugates with similar polarity are analyzed, one solvent extraction can be sufficient. However, for a total lipid extraction for a later fractionation to the individual classes of phytosterol conjugates, one must utilize combinations of extraction solvents to ensure maximum recovery. 

Abbreviations nr—not reported TAG—triacylglycerols FFA—free fatty acids St —phytosterol fatty acyl esters St—free phytosterols FPE—phytosterol ferulate esters tocols-tocopherols and tocotrienols GL—glycolipids PL—phospholipids RBD—refined, bleached, and deodorized oil. 

In the DOD, phytosterols are present in both the free and esterified forms with fatty acids. Therefore, the first step in the extraction of phytosterols is conversion of phytosterol fatty esters into free phytosterols. This is achieved either by hydrolysis or trani-esterification. Hydrolysis could be carried out under strong basic conditions (saponification with further acidulation), under strong acidic conditions, or under chemical or enzyme (specific or nonspecific) catalyzation. Re-esterification of phytosterols occurs during methyl ester distillation as a result of the high temperatures involved therefore, a further trani-esterification step for free sterols is required. Esterification of phytosterols or trani-esterification of sterol fatty acid esters is the second step in this process. Methanol is the most commonly used alcohol, and it leads to methyl esters, which are characterized by a higher volatility, however, other Ci to C4 alcohols may also be used. Esterification and trans-esterification of fatty acids or phytosterols can be catalyzed by metal alcoholates, or hydroxide, by organic catalysts, or by enzymes (Table 7). 

Abbreviations nr, not reported TAG, triacylglycerols FFA, free fatty acids St E, phytosterol fatty acyl esters St, free phytosterols FPE, phytosterol ferulate esters Tocols, tocopherols and tocotrienols GL, glycolipids PL, phospholipids and RBD, refined, bleached and deodorized oil. 

Com germ oil contains two phytosterol lipid classes, free phytosterols and phytosterol fatty acyl esters (Table 10.1). Phytosterols have been recognized as one of the twelve most important classes of phytonutrients (Fahey et al. 1999). Most chemical identification of phytosterols in vegetable oils has been conducted by saponifying (hydrolyzing with base) the oil and measuring the resulting free phytosterols, usually by GLC (Table 10.4). The major phytosterols... 

Their capacity to decrease serum low-density lipoprotein (LDL) cholesterol levels and, thus, in protecting against CVD, has led to the development of functional foods enriched with plant sterols. At present, several functional products, such as spreadable fats, yoghurts, and milk, with free phytosterols or phytosteryl fatty acid esters or phytostanyl fatty acid esters added at high levels, are available in the market, especially in several European countries. ... 

Ling WH, Jones PJH (1995) Enhanced efficacy of sitostanol-containing versus sitostanol-free phytosterol mixtures in altering lipoprotein cholesterol levels and synthesis in rats. Atherosclerosis 118(2) 319-331. doi 10.1016/0021-9150(95)05624-6... 

Figure 1. HPLC-ELSD chromatogram of corn fiber oil. Insert shows the structure of sitostanyl-ferulate, the major ferulate-phytosterol ester in corn fiber oil (Norton, 1995). Abbreviations StE, phytosterol fatty acyl ester TAG, triacylglycerol, a-Toc, a-tocopherol FFA, free fatty acids CE, p-coumarate-phytosterol esters y-Toc, y tocopherol ST, free phytosterols 1,3-D, 1,2-diacylglycerols FE, ferulate-phytosterol esters 1,2-D, 1,2-diacylglycerols.

Cmde com oil contains principally triglycerides and minor nonpolar and polar lipid components such as free fatty acids, phytosterol fatty acyl esters, free phytosterols, phytosterol femlate esters, tocols, tocopherols, tocotrienols glycolipids, phospholipids, pigments, volatile compoimds, waxes etc. (Gimstone, 2011). 

Research on maize fiber (Moreau et al. 1996) has shown that oil associated with the fiber fraction is different in composition compared to regular oil obtained from the germ. The fiber oil contains important amounts of ferulate phytosterol esters, free phytosterols, and fatty acid phytosterol esters, which lower serum cholesterol in laboratory animals. The most common class is ferulate phytosterol esters dominated by sitostanol, which is considered more efficient in lowering cholesterol. Phytosterols, such as ergosterol, campesterol, P-sitosterol, and stigmasterol, compete for cholesterol absorption, and therefore are considered hypocholesterolemic and preventive against CVD. According to Raicht et al. (1980) and Fiala et al. (1985) the supplementation of 0.2% P-sitosterol decreases the occurrence of chemically induced colon tumors. 

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