R. Przybylski

Stability of low linolenic acid canola oil to frying temperatures

The effect of heating on the oxidation of low (1.6%) linolenic acid canola oil (C18∶3) at frying temperature (185 ±5°C) under nitrogen and air was examined and then compared to a laboratory deodorized (9.0%, C18∶3) and a commercially deodorized (8.5%, C18∶3) canola oil sample. A significantly lower development of oxidation was evident for the low C18:3 canola oil, based on the measurement of peroxide value (PV), thiobarbituric acid (TBA), free fatty acids (FFA), dienals and carbonyls. The greater stability of the low C18:3 canola oil was also reflected by a corresponding improvement in heated room odor intensity scores. Heating under nitrogen (rather than air) not only improved the odors but limited the oxidation in all oils. While the low C18:3 canola oil heated under nitrogen was acceptable in 94% of odor judgments the same oil heated in air was acceptable in only 44%. This suggests that even low levels of C18:3 may contribute to the development of the heated room odor phenomenon.

Characterization of quinoa (Chenopodium quinoa) lipids.

Abstract Lipids isolated from quinoa seed and seed fractions were characterized for lipid classes and their fatty acid composition. Quinoa seed lipids contained the largest amount of neutral lipids among all the seed fractions analyzed. A very high content of free fatty acids was detected in whole quinoa seed and hulls, accounting for 18·9 and 15·4% of total lipids, respectively. Triglycerides were the major fraction present and accounted for over 50% of the neutral lipids. Diglycerides were present in whole seed and contributed 20% of the neutral lipid fraction. Of the phospholipids examined, lysophosphatidyl ethanolamine, was the most abundant and made up 45% of the total polar lipids. Phosphatidyl choline was the second largest phospholipid component and contributed 12% of whole seed phospholipids. Considerable variation in phospholipids was evident between the different fractions. The overall fatty acid composition of whole quinoa seeds, however, was similar to that reported for other cereal grains, with linoleic, oleic and palmitic acids as the major acids present.

Urinary chiro-inositol and myo-inositol excretion is elevated in the diabetic db/db mouse and streptozotocin diabetic rat.

Inositol phosphoglycan molecules containing either d-chiro-inositol or myo-inositol have been isolated from various mammalian tissues and are putative mediators of insulin action. Urinary excretion of inositols appears to be altered in diabetes mellitus; however, the relationships with different types of diabetes are unclear. The objective of this study was to determine the urinary excretion of chiro and myo-inosltol in diabetic animal models, including streptozotocin (STZ) rats, db/db mice, and fa/fa Zucker rats. In STZ rats (type 1 diabetes), 12-hr urinary excretion of chiro-inositol was elevated 336-fold and myo-inositol excretion was elevated 47-fold compared with their nondiabetic counterparts. When corrected for creatinine, chiro-inositol excretion was 259-fold higher and myo-inosltol excretion was 36-fold higher in STZ rats than in normal rats. The same pattern was observed in db/db mice (type 2 diabetes), where 12-hr urinary chiro-inositol excretion was elevated 247-fold compared with normal mice. When corrected for creatinine, chiro-inositol excretion was 2455-fold higher and urinary myo-inositol excretion was elevated 8.5-fold in db/db mice compared with normal mice. The fa/fa Zucker rats (impaired glucose tolerance) had a pattern of urinary inositol excretion that was similar to the nondiabetic animals (lean Zucker rats, C57BL/6 mice, and Sprague-Dawley rats). In summary, urinary chiro-inositol and myo-inosltol excretion was elevated in animal models of type 1 and type 2 diabetes mellitus, concomitant with hyperglycemia and glucosuria.

Phospholipid composition of canola oils during the early stages of processing as measured by TLC with flame lonization detector

Canola oils at initial stages of processing from different crushing plants were analyzed for phosphatides. The major phospholipid components identified and quantified in refined canola oils were phosphatidic acid and phos-phatidylinositol. Phosphatidic acid was the main phosphorus component identified in solvent extracted canola oil samples. The two-dimensional separation that was used combined classical thin-layer chromatography with quantitation on chromarods in an Iatroscan with a flame ionization detector. Phosphatides quantitated with this procedure ranged from 0.1 to 20 μg with a coefficient of variation of 4.4 to 7.2%. Using the modified procedure, recoveries of better than 90% were obtained for all phospholipids analyzed.

Degradation of phytosterols during storage of enriched margarines

Oxidative changes of phytosterols were recently studied in vegetable oils and some food products. Cholesterol-lowering properties of phytosterols and phytostanols are the main driver for formulating functional foods containing these compounds. Margarines enriched in plant stanols were stored at two typical temperatures for up to 18weeks. Analysed margarines contained four phytosterols: brassicasterol, campesterol, sitosterol, avenasterol and two phytostanols: sitostanol, campestanol. The content of phytosterols and phytostanols in margarines changed from 79mg/g in a control sample to 63mg/g and 55mg/g in samples stored for 18weeks at 4°C and 20°C, respectively. At the end of storage, contents of sitostanol decreased by 23% and 30%, while the amounts of oxidised sterols increased by 35% and 100%, respectively, for both temperatures. 7-Hydroxy derivatives dominated among all oxidised phytosterols and their content increased threefold at the end of storage. Epoxy derivatives exhibited a maximum after 6weeks of storage at 20°C and thereafter decreased constantly.

Sensory stability of canola oil: Present status of shelf life studies

Sensory studies on autoxidation of canola oil, stored under several variations of Schaal Oven test conditions, suggest an induction period of 2–4 d at 60–65°C. Similar induction periods have been observed between canola and sunflower oils, whereas a longer induction period has been found for soybean oil. Canola oil seems to be more stable to storage in light than cottonseed and soybean oils but is less stable than sunflower oil. Storage stability of products fried in canola oil is similar to products fried in soybean oil. Storage stability of canola and cottonseed oils that had been used in the frying of potato chips showed that canola oil was more prone to autoxidation during storage at 40°C. The presence of light aggravated the oxidative effects and was similar for both oils. Advances in our knowledge about the shelf life of canola oil would be strengthened by standardization of Schaal Oven testing conditions and by specifying the testing protocol for photooxidation studies. Methods for training of panelists and for handling and evaluating oils and fried foods require definition. Rating scales used in the evaluation of oils need to be evaluated to ensure that reliable and valid measurements are achieved. Further progress is needed in the identification of chemical indicators that can be used to predict sensory quality of oils.

Consumer acceptance of canola oils during temperature-accelerated storage

Abstract Ninety-two consumers judged the odour acceptability (yes or no) of regular (12·5% 18:3) and low linolenic acid (2·5% 18:3) canola oils which had been stored at 60°C for 21 and 42 days, respectively. For each storage day an average proportion of acceptance (APA) was calculated. Logistic regression analyses of storage days vs. APA yielded valid relationships for both oils. These equations permitted prediction of the number of days of accelerated storage for APA values from 0·4 to 0·8. The storage time to 0·5 APA, the consumer acceptance threshold, was 12·5 days for regular canola oil and 34·3 days for low linolenic acid canola oil, indicating substantially greater stability for the genetically modified caltivar. The frequency and character of free choice negative odour descriptors which were assigned to both oils at 0·5 APA were similar.

Phase transitions of canola oil sediment

Canola sediment was obtained from an industrial filter cake by solvent extraction. When heated in the differential scanning calorimeter (DSC) (5–100°C), the sediment exhibited a single narrow melting peak at around 74.8°C. No solid-state polymorphic transformation of the material could be detected over this temperature range. The X-ray powder diffraction pattern of canola sediment resembled waxes from other sources with an orthorhombic unit cell. The phase transition behavior of canola sediment in oil was studied by both DSC and polarizing microscopy. With increasing ratio of oil/sediment, a reduction in both melting temperature and transition enthalpy was observed. The shape of the supercooling curve resembled that of the melting curve. The induction time was determined by spectrophotometry and was used to calculate the interfacial free energyσ between sediment and oil; σ=4.71 erg/cm2. The effect of temperature and sediment concentration on the clouding time of canola oil was studied; the clouding time was the shortest at 5°C.

Formation and partial characterization of canola oil sediment

The occasional development of a haze in canola oil represents a problem to the quality and acceptability of this oil. The present study examined the formation of sediment in bottled canola oil during storage at 2, 6 and 12°C over a 4-d period. Oils stored at 2°C showed the highest rate of sediment formation, followed by storage at 6°C. Removal of sediment from canola oil prior to storage by cold precipitation and filtration did not eliminate this phenomenon, which still developed rapidly at 2°C. Chemical composition and thermal properties of canola oil sediment were compared to sediment obtained from commercial winterization of this oil. The thermal properties of the purified winterization sediment (melting temperature, 74.9°C) closely resembled those of the sediment from bottled canola oil. Saponification of both sediments yielded large amounts of long-chain fatty acids and alcohols, which were identified by gas chromatography-mass spectrometry. Sediment from commercial winterization contained higher amounts of fatty acids and alcohols with more than 24 carbon atoms in the chain.

Formation, analysis, and health effects of oxidized sterols in frying fat.

Publisher Summary Sterols, minor compounds present in dietary fat, comprise a major portion of the unsaponifiable matter of most vegetable oils. They are mainly present as free sterols and esters of fatty acids, in addition to sterol glucosides and acetylated. Vegetable oil sterols are collectively known as plant sterols or phytosterols. Sterols vary with the origin of the fat and are affected by food processing. Cholesterol is the main animal sterol, while β-sitosterol, campesterol, stigmasterol, brassicasterol, avenasterol, and stigmastenol are major plant sterols present in vegetable oils at much higher levels than cholesterol is in animal fats. Sterols share a similar chemical structure that undergoes oxidation in the presence of oxygen. This chapter provides an overview of the formation, analysis, and health effects of oxidized sterols in frying fat. It reviews the techniques used for the analysis of sterol oxidation products in food and biological matrices and discusses the health implications of phytosterol-oxidized products in addition to those reported for cholesterol-oxidized products. Oxidation products of cholesterol are of considerable interest because of their possible effects on human health. As more vegetable oil is used for cooking, it is necessary to consider the occurrence and effect of plant sterol oxides. This became particularly apparent when it was observed that vegetarians absorbed more phytosterols than did those on non-vegetarian diets. This implies that the effects could be greater than previously perceived. Work with oxidation products of plant sterols has expanded due to the availability of analytical methods.