We report the effects of individual steps of industrial refining, carried out in Brazil, on the alteration of selected minor constituents of oils, such as corn, soybean, and rapeseed oils. Total sterols, determined by capillary gas chromatography (GC), decreased by 18-36% in the fully refined oils, compared with the crude oils. The total steradienes, dehydration products of sterols, were determined via a simple clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with ultraviolet detection. The level of steradienes, normally not present in crude oils, increased after each refining step, especially after deodorization. Thus, the content of steradienes increased after deodorization by about 15-to 20fold in corn and soybean oils, and by about 2-fold in rapeseed oil. The total steryl esters were also determined via clean-up on a short silica gel column, followed by HPLC with evaporative light scattering mass detection. A minor decrease in the level of steryl esters was observed after complete refining. The individual tocopherols and tocotrienols were determined by HPLC with a fluorescence detector, q~he level of total tocopherols and tocotrienols decreased by about 2-fold after complete refining of corn oil and by about 1.5-fold in soybean and rapeseed oils. In all three cases, maximum reduction of tocopherols was observed after the deodorization step. The level of polymeric glycerides, determined via clean-up on a short silica gel column followed by size-exclusion HPLC, increased to some extent (0.4-1%) during refining. The level of trans fatty acids, determined by capillary GC, also increased to a substantial extent (1-4%) after refining.

Biodiesel consists of long-chain fatty acid esters, derived from renewable sources such as vegetable oils, and its utilization is associated to the substitution of the diesel oil in engines. Depending on the raw material, biodiesel can contain more or less unsaturated fatty acids in its composition, which are susceptible to oxidation reactions accelerated by exposition to oxygen and high temperatures, being able to change into polymerized compounds. The objective of this work was to determine the oxidative stability of biodiesel produced by ethanolysis of neutralized, refined, soybean frying oil waste, and partially hydrogenated soybean frying oil waste. The evaluation was conducted by means of the Rancimat  equipment, at temperatures of 100 and 105ºC, with an air flow of 20 L h -1 . The fatty acid composition was determined by GC and the iodine value was calculated. It was observed that even though the neutralized, refined and waste frying soybean oils presented close comparable iodine values, biodiesel presented different oxidative stabilities. The biodiesel from neutralized soybean oil presented greater stability, followed by the refined and the frying waste. Due to the natural antioxidants in its composition, the neutralized soybean oil promoted a larger oxidative stability of the produced biodiesel. During the deodorization process, the vegetable oils lose part of these antioxidants, therefore the biodiesel from refined soybean oil presented a reduced stability. The thermal process degrades the antioxidants, thus the biodiesel from frying waste oil resulted in lower stability, the same occuring with the biodiesel from partially hydrogenated waste oil, even though having lower iodine values than the other. Key words: Rancimat  , transesterification, oxidation ESTABILIDADE OXIDATIVA DE BIODIESEL DE ÉSTERES ETÍLICOS DE ÁCIDOS GRAXOS DE SOJARESUMO: Biodiesel consiste em ésteres de ácidos graxos de cadeia longa, proveniente de fontes renováveis como óleos vegetais, e sua utilização está associada à substituição do diesel em motores. Dependendo da matéria-prima, o biodiesel pode conter mais ou menos ácidos graxos insaturados em sua composição, que são suscetíveis a reações de oxidação aceleradas pela exposição ao oxigênio e altas temperaturas, podendo resultar em compostos poliméricos prejudiciais ao motor. O objetivo deste trabalho foi avaliar a estabilidade oxidativa do biodiesel obtido pela etanólise dos óleos de soja neutro, refinado, usado em fritura, e óleo parcialmente hidrogenado usado em fritura. A avaliação foi feita através do equipamento Rancimat . A composição em ácidos graxos foi determinada por CG e o índice de iodo calculado. Embora os óleos de soja neutro, refinado e usado em fritura apresentassem índices de iodo próximos, a estabilidade oxidativa do biodiesel comportou-se de maneira distinta. O biodiesel de óleo neutro apresentou maior estabilidade, seguido pelo refinado e usado em fritura. Por conter antioxidantes naturais em sua composição, o óleo neutro de soja proporcionou uma es...

Steryl esters of fatty acids have been isolated from vegetable oils by rapid chromatography on a short column of silica gel and quantitatively determined by HPLC on RP-18 columns using an evaporative light scattering detector that was calibrated with β-sitosteryl oleate as external standard. The steryl esters isolated according to the above technique from corn, soybean, and rapeseed oils at different stages of industrial refining have been analyzed for their constituent sterols and fatty acids by GC. Moreover, the total sterols were analyzed by GC. In all three oils a substantial part of the sterols occurred as steryl esters. Some alterations in the composition of the constituent sterols and fatty acids of the steryl esters were observed during industrial processing. Keywords: Industrial fat refining; HPLC; sterols; steryl esters; vegetable oils

Steryl ester content of refined and interesterified corn, soybean, and rapeseed oils has been measured via cleanup on a short silica gel column, followed by high performance liquid chromatography with evaporative light-scattering mass detector. Chemical interesterification, catalyzed by sodium methoxide, led to random positional distribution of fatty acids in triacylglycerols and some increase in the steryl ester content of all three oils. Enzymatic interesterification, catalyzed by the immobilized lipase from Rhizomucor miehei (Lipozyme), resulted in a distinct reduction in steryl ester content, but essentially no alteration in positional distribution of fatty acids in triacylglycerols occurred. Formation of steryl esters during chemical and enzymatic interesterification was also examined by radioactive tracer technique with [4-14 C]β-sitosterol added as marker to refined rapeseed oil and measurement of the radioactive steryl esters formed. Chemical interesterification of rapeseed oil resulted in moderate formation (10% of total radioactivity) of radioactive β-sitosteryl esters. Enzymatic interesterification of the oil, catalyzed by Lipozyme, led to little formation of radioactive β-sitosteryl esters, whereas with the lipase from Candida cylindracea high proportions (>90% of total radioactivity) of 14 C-labeled β-sitosteryl esters were formed. JAOCS 74, 93-96 (1997). KEY WORDS:Candida cylindracea lipase, chemical interesterification, enzymatic interesterification, positional distribution of fatty acids, radioactive tracer technique, Rhizomucor miehei lipase, β-sitosterol, steryl esters.Sterols occur in plant oils partly as unesterified sterols and partly as steryl esters of fatty acids, in addition to steryl glycosides and esterified steryl glycosides (1,2). We have recently developed a method for quantitative determination of steryl esters in oils by clean-up on a short silica gel column, followed by high-performance liquid chromatography (HPLC) with detection by means of an evaporative light-scattering mass detector (Ferrari, R., E. Schulte, and K.D.Mukherjee, manuscript in preparation). The above method was used to monitor changes in steryl esters in plant oils at different stages of industrial refining (Ferrari, R., E. Schulte, and K.D. Mukherjee, manuscript in preparation). Here we report the alterations in steryl ester content of plant oils by interesterification, e.g., chemical interesterification (randomization) catalyzed by sodium methoxide, and enzymatic interesterification catalyzed by lipase from Rhizomucor miehei (Lipozyme). Moreover, we report the formation of steryl esters during chemical interesterification and enzymatic interesterification of rapeseed oil, catalyzed by Lipozyme and the lipase from Candida cylindracea, as monitored by a radioactive tracer technique. [4-14 C]β-Sitosterol was added as marker to the oil, and the formation of radioactive steryl esters during interesterification was followed. EXPERIMENTAL PROCEDURESMaterials. Refined corn oil was a product of Rafinacoes de milho Brasi...