Polyunsaturated fatty acids peroxide value

PTFE polytetrafluoroethylene PUFA polyunsaturated fatty acid PV peroxide value PVDF polyvinylidene difluoride PVP polyvinylpyrrolidone PVPP polyvinylpolypyrolidone RAS retronasal aroma stimulator RDA recommended dietary allowance RF radio frequency RFI relative fluorescence intensity RI retention index RNU relative nitrogen utilization ROESY rotational nuclear Overhauser enhancement spectroscopy RP-HPLC reversed-phase HPLC RPER relative protein efficiency ratio RS resistant starch RT retention time RVP relative vapor pressure S sieman (unit of conductance)... 

Peroxide value (P V) is the most commonly used measurement of lipid oxidation. The standard iodometric method requires a relatively large sample (5 g) when the lipid is only slightly oxidized. The ferric thiocyanate method, based on the oxidation of ferrous to ferric ion, involves colorimetric measurement of ferric thiocyanate. This method is more sensitive than the iodometric method and requires a relatively small sample (0.1 g). The PV is a useful measure for samples with low levels of oxidation and when the hydroperoxides are not decomposed. During prolonged oxidation, a maximum PV is reached and the value then begins to decrease due to peroxide degradation. This maximum value occurs early for soybean and rapeseed oil, due to the more rapid decomposition of the hydroperoxides of the polyunsaturated fatty acids. 

Another processability factor is TOTOX value that is related to the degree of oil deterioration due to lipoxygenase action on polyunsaturated fatty acids in the oil (Mounts et al., 1990). Products of oxidation degrade flavor and stability of edible oils. A low TOTOX value <3.0 meq/kg is desirable. TOTOX was calculated as two times the peroxide value as determined by AOCS Method Ca9f-57 plus the anisidine value (AOCS, 1987). 

The high stability of the macadamia nut oil may be associated with the storage conditions and the xmsaturated fatty acid profile, which is an important factor since the unsaturations make the oil less susceptible to oxidation. Therefore, macadamia nut oils have high oxidative stability due to the high content of monounsaturated and polyunsaturated fatty acids. Low peroxide and acidity values are also responsible for high oxidative stability since they are associated with the quality standards and conservation of raw materials [28]. 

Feeding menhaden (fish) oil at 2% of the dry matter intake of the diet also lowered milk fat concentrations. The level of CL A was increased by approximately 3.6 fold, but there was also a concurrent 4-5 fold rise in the level of vaccenic acid. Increasing the oil intake to 3% had no additional effects. The level of n-3 fatty acids in the milk was increased, mainly due to increased levels of eicosapentaenoic acid (EPA 20 5n-3), as was the level of total trans monoenes. The effects of pasteurization and oxidation on the raw milk were examined but no significant changes were observed and the CLA isomer profile was unchanged. There were no significant flavour differences found between the milk (and butter made from the milk) of cows fed 2% menhaden oil and control samples. The higher polyunsaturated fat content of the butter meant that it was softer at 4°C and 20°C, but the acid value and peroxide value of the butter were similar to those of control samples even after 3 months. A consumer evaluation of milk from cows fed a fish oil diet found no difference in acceptability compared with the control milk (Ramaswamy et al, 2001). 

During long-term storage biodiesel can be easily subject to oxidation under ambient conditions due to the presence of double bonds in the chains of fatty compounds. The reaction of oxidation increases with the increasing of unsaturation level (polyunsaturated compounds are many times more reactive that monounsaturated ones). Some parameters such as acid value, peroxide value or kinematic viscosity increase when autoxidation occurs, thus the fuel s quality is affected. Degradation of the quality of this alternative fuel leads to an increase of deposits on injectors and pump parts and therefore an increase in pressure across filters. 

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