Oxidative quality/stability tests

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. 

Polymer applications of DSC are numerous and concern the determination of Tm (ASTM E 794), Tg (ASTM E 1326-03, ISO/FDIS 11357-2), specific heat capacity of a material (ASTM E 1269, ASTM D 4816), crystallisation temperature upon cooling (ASTM E 794), transition temperatures (ASTM D 3418, ASTM D 4419, ASTM D 4591), purity of a material [79,80], contamination outgassing (ASTM E 1559), reaction rates, sample composition, reaction kinetic constants (ASTM E 698), reaction mechanisms, thermal stability (ASTM E 537), minimum processing temperatures, heat of fusion and crystallisation (ASTM D 3417), heat of crystallisation (ASTM E 793), additive effects on a material, quality control of raw materials [25], discrimination between materials, detection of polymorphism [81], characterisation of thermally and UV cured materials (cure state, degree of cure) (ASTM D 2471, ASTM D 5028), oxidative stability testing, QIT (ASTM D 3895, ASTM D 3012, ASTM E 1858-03), etc. 

The purpose of in-use stability studies is to establish the period for which a product intended to be used on more than one occasion may be used after reconstitution or dilution or the withdrawal of the first dose from the container without adversely affecting the integrity of the product and with the product retaining acceptable quality characteristics. This type of test can be applied to any multiple use product (e.g., sterile products in multiple-use containers, powders or granules including those used to produce oral solutions or suspensions) but is likely to be of particular importance in the case of products that are manufactured with an inert headspace gas, for products containing antioxidants to protect an active ingredient that is liable to oxidative decomposition, and for products that contain a volatile antimicrobial preservative. 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

Hair dyes must meet a number of conditions related to their end use. Color can be assessed by colorimetry [49], The limits of precision are set by the substrate on which the measurement is performed. Studies on test subjects are difficult because of the uneven natural hair color and the background color of the scalp. Tresses are hard to prepare at a constant quality level. Measurements on wool cloth give reproducible results, but for oxidation dyes the shades are not identical to those produced on hair. Colorimetric methods are therefore useful only for comparative measurements on the same object, for example, in lightfastness tests. Because hair must be redyed after four to six weeks due to growth, the fastness required of hair dyes is generally less than that needed for textiles. However, stability is still a problem with many indo dyes (see Section 5.4.3). Some of them... 

The measurements of water quality parameters (oxidation-reduction potential, pH, temperature, conductivity, dissolved oxygen, and turbidity) and the collection of field screening data with field portable instruments and test kits constitute a substantial portion of field work. Field measurements, such as pH, stand on their own as definitive data used for the calculations of solubility of chemical species and chemical equilibrium in water, whereas others serve as indicators of well stabilization or guide our decision-making in the field. Table 3.8 shows the diversity of field measurement... 

These full synthetics have been all PAO or ester based, and a mixture of ester plus PAO. The addition of PAO or ester to petroleum based engine oils for improved oxidative stability has shown average quality results. The addition of lower levels of PAO or ester base stock <15 wt % to petroleum based formulations show little or no improvement in the thermo-oxidative engine test. The predominant automotive synthetic base stocks (PAO, diesters, polyol esters) do not show any hydrolytic instability in engine oil applications. 

The stability of this surface against hydroxylation was tested by extensively dosing the surface with up to 10 Langmuir of H2O at 3-10 mbar partial pressure at room temperature. Similarly to the single crystal case, no stmctural effect could be detected. This stands in contradiction with the NiO(l 11) films of poor structural quality made by oxidation of Ni(lll) [132, 140], which were found unstable against hydroxylation. We thus suggest that the reactivity of NiO(l 11) against water takes mainly place at defects (like for MgO), which are almost absent on our surfaces and thin films. 

Regardless of the official specifications for soybean oil and its products, the ultimate proof of the pudding is in the eating that is, sensory evaluation of the odors and flavors of soybean oil and its products is the ultimate method to assess oil quality and stability. Sensory evaluation cannot be replaced fully by any chemical or instrumental analysis, although some methods can correlate fairly well with sensory results. Sensory evaluation of oils usually is done by a panel of experts or a trained panel, and often the method recommended by the American Oil Chemists Society (300) is used. During the evaluation, the panel is asked to score the overall flavor quality, as well as the intensity of many individual off-fiavors. Although chemical and physical tests are more reproducible and less time consuming than sensory evaluations, oxidative rancidity and off-flavor evaluation of soybean oils are best done by sensory tests. Correlations established between sensory evaluation scores and... 

General aspects of petroleum quality (as a refinery feedstock) are assessed by measurement of physical properties such as relative density (specific gravity), refractive index, or viscosity, or by empirical tests such as pour point or oxidation stability that are intended to relate to behavior in service. In some cases the evaluation may include tests in mechanical rigs and engines either in the laboratory or under actual operating conditions. 

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