Oil Quality Indices

This unit defines three different tests that are used to evaluate lipid systems. The first two, i.e., iodine value (IV see Basic Protocol I) and saponification value (SV see Basic Protocol 2), are used to determine the level of unsaturation and the relative size (chain length) of the fatty acids in the system, respectively. The free fatty acid (FFA) analysis (see Basic Protocol 3) is self-explanatory. Each of these analyses provides a specific set of information about the lipid system. The IV and SV provide relative information this means that the data obtained are compared to the same data from other, defined lipid systems. In mixed triacylglyceride systems there is no absolute IV that indicates the exact number of double bonds or SV that indicates the exact chain length. The data from the FFA analysis is an absolute value however, the meaning of the value is not absolute. As a quality indicator, ranges of FFA content are used and the amount that can be tolerated is product and/or process dependent. 

The iodine value (IV) is used to determine the level of unsaturation in a fat/oil system. It is expressed as the number of grams of iodine that add to/react with 100 g of sample. The traditional iodine value method using the Wijs reagent requires carbon tetrachloride (CC14). For safety reasons, CC14 is no longer considered to be an acceptable chemical and it is not readily available for purchase, and if offered it is extremely expensive. Therefore the traditional method has been modified to a more human-friendly system which uses cyclohexane. 

CAUTION Wijs solution is hazardous and should be handled with gloves in a fume hood. Materials 

Fat or oil sample to be analyzed Sodium sulfate (anhydrous optional) 

Wijs solution, in glacial acetic acid (Fisher Scientific store in the dark at 25° to 30°C and keep tightly sealed) 

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Iodine, colorimetric determination of amylase using, 689-692 Iodine value, lipid composition canola oil, 474 (table) oil quality indices, 467-469, 475-477 lodometric titration, determination of peroxide value, 518-519 Ionization techniques, in mass... 

British panel. Note that the sensory attributes are to some extent different. Table 35.3 gives some information on the country of origin and the state of ripeness of the olives. Finally, Table 35.4 gives some physico-chemical data on the same samples that are related to the quality indices of olive oils acid and peroxide level, UV absorbance at 232 nm and 270 nm, and the difference in absorbance at wavelength 270 nm and the average absorbance at 266 nm and 274 nm. 

The specific quality indices are seed moisture, < 6% total ash, 7% acid-insoluble ash, 1.5% volatile oil, minimum 2% foreign organic matter, 2%. 

Fruits and juices have been investigated by a number of researchers. Schamp and Dirinck ( 5) found over forty compounds in a study of strawberry varieties, as well as finding 22 compounds in Golden Delicious apples. Keenaghan and Meyers ( ) reported on the GC/MS identification of over twenty different compounds in several varieties of apples and apple products. Additional work with apples has been reported by Westendorf ( 7) This same paper reported the analyses of dairy products, vegetable oils, and artificial flavors. Edible oils have been extensively studied since the presence of volatiles was first recognized as an indicator of oil quality (8). Considerable work with oils and oil-based foods using manual procedures has been reported by Jackson et al. (9,H)), Dupuy et al. (jU, 1 2), and Selke (1 3). In 1983 Roberts (F4) first reported the use of an automated DHA procedure for oil volatiles. 

When 4 wt% polyethylene terephthalate (PET), derived from used soft-drink bottles, was added to the PE, no decline in lube quality was observed, with hydroisomerization giving a 160 VI 5 cSt oil. This indicates that a high degree of separation of the waste plastic may not be necessary, which would lower the cost of feedstock to the process. 

Analytical methods for measuring hydroperoxides in fats and oils can be classified as those determining the total amount of hydroperoxides and those based on chromatographic techniques giving detailed information on the structure and the amount of specific hydroperoxides present in a certain oil sample (8). The PV represents the total hydroperoxide content and is one of the most common quality indicators of fats and oils during production and storage (9, 18). A number of methods have been developed for determination of PV, among which the iodometric titration, ferric ion complex measurement spectrophotometry, and infrared spectroscopy are most frequently used (19). 

Steam used to recover oil from earth Chemists learned that FFA level in crude cottonseed oil was a good quality indicator Removed the objectionable flavors and odors from the oil Process to convert a liquid oil to a semi-solid... 

The oil is either improperly processed or it is derived from poor-quality crude if the fresh oil analysis indicates the following ... 

The Merck Company of Darmstadt, Germany developed the OXIFRIT FRIT-EST to measure oil quality in frying operations, especially in restaurants. The Fritest measures the alkali color number to indicate oxidized fatty acid (OFA) and the Oxifrit Test measures oxidation products in the fryer oil. Both tests are colorimetric and use a solvent-based reagent system. The test methodology is too comphcated for the restaurant personnel. 

Petroleum lubricating oils are sometimes characterized by their density. As will be seen when we come to the examination of chemical structures in lubricating oils later in this chapter, density is associated with structural type. Paraffinic oils are lower in density than naphthenic or aromatic oils. Since paraffinic oils show more desirable viscosity-temperature behavior and better thermal stability than naphthenic oils, in the past density was widely used as an easily measured indicator of oil quality. With the development of additives to improve viscosity and thermal stability behavior, classification of oils by their density ratings has lost much of its former importance. 

Wang and Johnson (2001) reported on test measurement methods that were major indicators of soybean oil quality. These tests included peroxide value, anisidine value, FFA content, phospholipid content, total tocopherol content, oxidative stability index, color, and moisture content. For soybean meal, they reported on urease activity, protein dispersibility index (PDI), rumen bypass or rumen undegradable protein, trypsin inhibitor activity, moisture content, residual oil content, protein content, fiber content, color, amino acid profiles, and protein solubility under alkaline (KOH) conditions. 

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