Storage oxidation stability

Stability—In petroleum products, the resistance to chemical change. Gum stability in gasoline means resistance to gum formation while in storage. Oxidation stability in lubricating oils and other products means resistance to oxidation to form sludge or gum in use. 

Safety risks and the environmental impact are of major importance for the practical success of bromine storage system. The nonaqueous polybromide complexes in general show excellent physical properties, such as good ionic conductivity (0.1-0.05 Qcirf1), oxidation stability (depending on the nature of the ammonium ion), and a low bromine vapor pressure. The concentration of active bromine in the aqueous solution is reduced by formation of the complex phase up to 0.01-0.05 mol/L, hence ensuring a decisive decrease of selfdischarge. 

The time to reach a certain PV may be used as an index of oxidative stability for food lipids. The effects of antioxidants and food processing on fats are often monitored in this way. Thus, a longer time period to reach a certain PV is generally indicative of a better antioxidant activity for the additive under examination. However, a low PV represents either early or advanced oxidation the breakdown of peroxides to secondary oxidation products will result in a decrease in PVs during the storage period. For determination in foodstuff, a major disadvantage to the classical iodometric PV assay is that a 5-g test portion is required it is sometimes difficult to obtain sufficient quantities of lipid from foods low in fat. Despite its drawbacks, PV determination is one of the most common tests employed to monitor lipid oxidation. 

The oil stability index (OSI) method provides results in a matter of hours instead of months (required for studies done at ambient temperatures). These OSI results are useful as comparative measures of oxidative stability, i.e., to determine the effect of a treatment or antioxidant compared to a control sample. Meaningful predictions of the actual shelf lives of specific commodities require that such shelf life studies be performed at ambient conditions. If only accelerated tests are to be performed, two or more tests based on different principles of lipid oxidation measurement should be conducted the effect of accelerated storage temperature should also be investigated. 

H Stapelfeldt, BR Nielsen, LH Skibsted. Effect of heat treatment, water activity and storage temperature on the oxidative stability of whole milk powder. Int Dairy J 7 331-339, 1997. 

Cloned, pH stability, Temperature stability [°C], Organic solvent stability, Oxidation stability, General stability, Storage stability, Renatured, and Links to other databases and references. 

Higher alcohol content may cause the degradation of rubber gaskets and should be limited to under 1%. The acidity number reflects the presence of free fatty acids, which can contribute to accelerated engine aging. For the same reasons the water content should be kept quite low, at max. 300ppm. Finally, in order to ensure proper storage the oxidation stability of the fuel should be at least 5h at 110°C. 

The maximum shelf-life of bulk packaged WMP containing 3% moisture is about 6 months at 30°C (Kjaergaard Jensen, 1988). The oxidation of WMP, as measured by peroxide value, is dependent on the moisture content of the powder, van Mil and Jans (1991) reported that under similar storage conditions, the peroxide value of WMP increases more rapidly for powder containing 3% moisture than in powder containing 2.4% moisture. The water activity (aw) range for WMP is usually 0.13 0.20, with a typical value from 0.16 to 0.18 (Wewala, 1990). Stapelfeldt et al. (1997) found that the quality of WMP is maintained best at aw between 0.11 and 0.23, whereas the quality of the powder decreases when stored at aw of 0.31 at 45°C. However, the critical aw for improved oxidative stability of WMP stored at 40°C for one year is 0.21 0.24 at a moisture level of 3.4% (Wewala, 1990). 

The effect of storage temperature on the oxidative stability of milk and milk products is unclear. Storage, in air, at 2°C inhibited the development of oxidized flavor in dry whole milk when compared with control samples held at 38°C (Pyenson and Tracy, 1946). Oxidative deterioration of UHT cream occurred two to three times more rapidly at 18°C than at 10°C, while little or no oxidation occurred at 4°C (Downey, 1969). The oxidation-reduction potential of butter and the rate of flavor deterioration have been reported to increase as the storage temperature increased (Weihrauch, 1988). 

Although there are numerous publications on the effect of natural and synthetic antioxidants on the stability of oils and fats used as food and feed, until recently relatively little publicly available information was available on the effect of antioxidants on the oxidative stability of biodiesel. One of the earliest studies reporting of the effects of antioxidants on biodiesel was that of Du Plessis et aL (1985), which examined storage stability of sunflower oil methyl esters (SFME) at various temperatures for 90 d. Effects of air temperature, presence of light, addition of TBHQ (see Figure 1.1) and contact with steel were evaluated by analysis of free fatty acid content, PV, kinematic viscosity, anisidine value, and induction period. Addition of TBHQ delayed oxidation of samples stored at moderate temperatures (<30°C). In contrast, under unfavorable (50°C) conditions, TBHQ was ineffective. 

Loh, S. K., Chew, S. M., and Choo, Y. M. 2006. Oxidative Stability and Storage Behavior of Fatty Acid Methyl Esters Derived from Used Palm Oil. I. Am. Oil Chem. Soc., 83, 947-952. 

Oxidation Stability (OSI or Rancimat) has been introduced in many ways. In EN14214 it exists as OSI and as a maximum acceptable Iodine Value, or maximum level of linolenic acid or of poly-unsaturated fatty acids. Oxidation stability is of importance when it comes to polymerization and oxidation during storage as well as during use in the engine. Oxidation is directly related to the presence of unsaturated bonds in the FAME, and probably because of this the EN 14214 includes a cap on Iodine Value. 

Heinzelmann, K., Franke, K., Velasco, J., and Marquez-Ruiz, G. (2000). Micro-encapsulation of fish oil by freeze-drying techniques and influence of process parameters on oxidative stability during storage. Fur. Food Res. Technol. 211,234 239. 

The expected life of a diesel fuel is indicated by the oxidation stability test (ASTM D-2276). The test measures how much gum and sediment will be deposited after conditioning the fuel at 120°C in the presence of oxygen for 16 h. It roughly corresponds to a years storage at 25°C. A result of less than 20 mg/L of sediment and gum after the test is considered acceptable for normal diesel. 

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