ABSTRACT
Sterols constitute a large group of compounds with a broad range of biological activitiesandphysicalproperties.Theyarederivativesofsteroidsandarecommonin eukaryoticcellsbutrareinprokaryotes.Thenaturaloccurringsterolsusuallyhave a1,2-cyclopentano-phenanthreneskeletonand27-30carbonatomswithahydroxyl groupatC-3andsidechainofatleastsevencarbonatC-17.Sterolsareminorconstituents present in the fat of the human diet. They comprise the major portion of the unsaponiŒablefractionofmostediblefatsandoil.SterolscanbeclassiŒedaccordingtotheiroriginasanimalsterolsorasplantsterols.Thelattercanbesubdivided intophytosterols(higherplantsterols)andmycosterols(lowerplantsterolspresent inthelipidfractionofyeastandfungi).Cholesterolisthemainanimalsterol,while
7.1 Introduction .................................................................................................. 113 7.2Cholesterol .................................................................................................... 114
7.2.1Structure and Occurrence ................................................................. 114 7.2.2Methods of Reducing Cholesterol in Foods ..................................... 115 7.2.3Cholesterol and Its Relationship to Atherosclerosis ......................... 116 7.2.4 Oxidation of Cholesterol ................................................................... 117 7.2.5Biological Effects of Oxysterols ....................................................... 120
7.3Phytosterols ................................................................................................... 120 7.3.1Structure and Occurrence ................................................................. 120
7.3.1.1Plant Sterols in Food Products ........................................... 123 7.3.1.2 Food Products Enriched in Phytosterols and
Phytostanols ......................................................................124 7.3.2Bioactivity of Phytosterols ................................................................ 125 7.3.3Changes of Phytosterols during Food Processing ............................ 125
7.3.3.1Oxidation ........................................................................... 125 7.3.3.2 Polymerization ................................................................... 127 7.3.3.3Thermal Degradation ......................................................... 127
Acknowledgment ................................................................................................... 130 References .............................................................................................................. 130
sitosterol, campesterol, and stigmasterol are the major plant sterols. These phytosterolsandcholesterolareall4-desmethylsterolsthatshareidenticalringstructures.The varioussterolsdifferonlyintheirsidechain.Surprisingly,theseminordifferences resultinmajorchangesinbiologicalfunctions.Theyarewidelydistributedinnature, andoccurbothinthefreeformor,mostfrequently,asestersofhigheraliphaticacids and glycosides. Sterols, sterol esters, and sterol glycosides are, to different degrees, soluble in fats but completely insoluble in water.
