N. A. M. Eskin

Quality control in the use of deep frying oils

The chemical and physical changes that occur in frying facts during use and their significance to fat life and to finished product quality are reviewed. The more commonly used quality control tests for monitoring these changes are examined as is their applicability to food service institutions and food processors. The advantages and disadvantages of these tests and possible modifications to improve their ease for on-the-spot testing are discussed. Chemical tests such as free fatty acids (FFA), thiobarbituric acid (TBA) tests and peroxide value (PV) are available to those operations with laboratory facilities, whereas sensory and physical tests, including foam height, color, smoking, viscosity, odor and product flavor, are generally relied on by most food service facilities for on-the-spot assessment. The reliability of these tests, however, depends on the source and type of frying fat, the food being fried, and, in the case of the sensory and physical tests, on the skill and experience of the operator. Studies completed recently in this laboratory found a high correlation between polar compounds or FFA and length of frying time which suggests that either could predict oil abuse accurately. Recent adaptations which could facilitate on-the-spot testing by semi-skilled personnel (including a spot test for FFA and an instrument capable of monitoring the change in dielectric properties of an oil during frying) will be examined. Regardless of the quality control test used, the question remains of specifying reliable cutoff levels which can be related to the health and sensory constraints. This problem is also discussed.

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.

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.

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.

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.

Characterization of stored regular and low-linolenic canola oils at different levels of consumer acceptance

A ten-member trained sensory panel evaluated regular (RCO) and low-linolenic (LLCO) canola oils that had been stored at 60°C to four levels of consumer acceptance identified in a prior study. These levels were 70, 60, 50, and 40% acceptance for RCO and 80, 70, 60, and 50% acceptance LLCO. Painty odor intensity increased as consumer acceptance decreased. This same trend was found for chemical measurements of peroxide values, total volatiles, total carbonyls, unsaturated carbonyls, and dienals. These chemical indices were significantly correlated with each other, suggesting that they can be used to monitor related changes in oil quality with respect to lipid oxidation. Values for 19 individual volatiles at each consumer acceptance level were also reported. The data collected in this study provide chemical and sensory characterization of stored RCO and LLCO at distinct levels of consumer acceptance.

Comparison of the composition and properties of canola and sunflower oil sediments with canola seed hull lipids

The phase transition behavior and chemical composition of sediments from Canadian and Australian canola oils, as well as from sunflower oil, were studied by differential scanning calorimetry, X-ray diffraction, polarized-light microscopy, and chromatographic techniques. Australian canola sediment was similar to Canadian canola sediment in both melting and crystallization behaviors and chemical composition. Compared to canola sediment, sunflower sediment underwent phase transformation (melting and crystallization) at lower temperatures, and the enthalpies associated with the phase changes were greater. The X-ray diffraction patterns for these materials were similar, indicating identical crystalline structures. Sunflower sediment contained mainly wax esters (99%), while canola sediment contained about 72–74% of waxes. Moreover, sunflower sediment consisted of shorter-chainlength fatty acids and alcohols than canola sediment. A hexane-insoluble fraction from Canadian canola hull lipids had fatty acid and alcohol profiles and X-ray diffraction pattern similar to the corresponding oil sediment.

A simple and rapid method for assessing rancidity of oils based on the formation of hydroperoxides

A new colorimetric method is reported for determining rancidity of oil based on the complex formation between titanium and lipid hydroperoxides present in the oil. This method was highly correlative with peroxide value (PV) and thiobarbituric acid (TBA) methods as well as with odor intensity value (OIV).

Effects of crystallization conditions on sedimentation in canola oil

The effects of various factors on sediment formation in canola oil were studied. The crystallization temperature of sediment varied with cooling rate, whereas the melting temperature depended on heating rate as well as the cooling rate during sediment formation. The final crystal size depended on cooling rate. The crystal habit of sediment was generally rod-like but could change to a round and leaf-like shape at low cooling rates (<0.5°C/min). Crystal nucleation occurred in the initial stage of crystallization, while crystal growth was observed during the whole crystallization process, decreasing as cooling proceeded. Crystal growth rate of the sediment was proportional to the crystal surface area Lecithin did not affect the phase transition temperatures of sediment, but retarded crystal growth.