Thermally induced reactions occurring in lipids under nonoxidative conditions are reviewed. Free fatty acids may be formed in both the absence and presence of moisture. In thermal hydrolysis of triglycerides, there is a preferential release of the shorter-chain and the unsaturated fatty acids, but no positional specificity is observed. The mechanisms of formation of lactones, methyl ketones, hydrocarbons, and monocarboxylic and dicarboxylic methyl esters in heated fats are discussed.

The effects of various antioxidants and RH on the oxidative stability of microencapsulated fish oil powder were investigated using PV and thiobarbituric acid tests. The microencapsulation process provided high encapsulation efficiency (≥88% of extractable fish oil). Without antioxidants, the encapsulated fat was 10 times more stable against oxidation than the surface fat, as determined by PV. α-Tocopherol, which is a lipophilic antioxidant, showed a greater antioxidative effect in both surface and encapsulated fats than ascorbyl palmitate, which is an amphiphilic antioxidant. According to TBARS values, the longest lag period was observed at 0% RH. Addition of >200 ppm α-tocopherol in a 10-30% RH range prolonged the oxidative stability of the microencapsulated fish oil powder.

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Sinre prehistoric times. prople ha\,e heen using hent in the ~rroaration o r thcir food 11) modify its flavor or texture and to improve its ability to he stored.~ost of the food we consume today has been subjected to varied degrees of heat treatment at one stage or another,

The purpose of this study was to investigate the effects of temperature, oxidation time, presence of water, pH, type of buffer and form of substrate used on cholesterol oxidation. Microcrystalline cholesterol films, both solid and melted, and aqueous suspensions of film fragments were used as substrates. Use of dispersing agents was avoided. Quantitative analysis of the unaltered substrate and the products of its autoxidation was carried out by gas chromatography over the course of oxidation. Solid cholesterol films were found to be resistant to autoxidation in the dry state. However, when heated at 125 degrees C, a sudden increase in oxidation rate occurred at a point coinciding with the visible melting followed by a plateau of the oxidation rate. All of the autoxidation products formed underwent further decomposition. Film fragments of cholesterol oxidized at a faster rate in aqueous suspensions than when oxidized in the dry state. In aqueous suspensions, the differences in the resistance of cholesterol to oxidation were not significant within the pH range 6.0-7.4, except for the early stages of oxidation. The 7-ketocholesterol/7-hydroxycholesterol ratio dropped significantly with increasing pH. However, at all pH levels tested, this ratio remained relatively constant during the 6 h of heating. While the 7 beta-hydroxycholesterol/7 alpha-hydroxycholesterol ratio was not affected by pH in the range of 6.0-7.4, at pH 7.4 a high preference was observed for the cholesterol beta-epoxide over its alpha-isomer.(ABSTRACT TRUNCATED AT 250 WORDS)