subject: What affect the oil anisidine value and peroxide value [print this page] What affect the oil anisidine value and peroxide value
The initial product of lipid oxidation are peroxides, measured in the quantitative number of free iodine released from the reaction of potassium iodide and oil, the peroxide value is the number of milligrams of iodine per kilogram oil, which is a measure to indicating initial oil oxidation.
These oxides are unstable, can be decomposed into small molecular complex compounds such as aldehydes, ketones, acids, etc., can damage the body's normal physiological function of cell membranes, promote and develop the disease, so the amount of decomposition products is an important indicator to measure the quality of oils and fats It is anisidine value expressed in, also known as Ani cefoxitin value (P-Anisidine). Factors that affect the degree of lipid oxidation summed up as follows:
1, the produce of oxides connects with the temperature, air concentration, the higher the temperature and air concentration, the reaction faster, higher peroxide. The hermal decomposition of peroxides are compounds such as aldehydes and ketones, mainly 2 - aldehyde and 2,4 - diene aldehyde. Some of these compounds are small molecules, with special odor and volatile,can be removed through the deodorization, some macromolecular compounds, still triglyceride form, is not volatile, usually tasteless, and can not be removed by deodorization method. It acts as a catalyst for further oxidation. The higher the concentration, the stronger the catalytic ability.
2. The oils in the form of seeds are less prone to oxidation, when the seeds are broken or long time stored up,the peroxide value of oils and fats can also increase, while the peroxide can damage anti-oxidants in the seed cells , thus speeding up the oxidation.
3, squeezing can damage the natural antioxidants in oil, so that the fat oxides, even more under high temperature and pressure. When the oil out of oil export by the press, the air in oil can reach saturation level, whch increases lipid peroxide value by 3-4meq/kg.
4. With the increase of storage temperature, time extension and air content, the peroxide value of crude oil also rises. Oxidation is a chain reaction: the higher the peroxide value, the faster the formation of peroxides. With vacuum-pumping or nitrogen blanketing in the oil, the oxidation reaction can be prevented from continuing. The anisidine value of crude oil is usually low, generally 1-3, but the crude oil produces the peroxide decomposition and molecular fragments after heating, the anisidine value will rise.
5, Normally oxidation does not occur during Alkali refining process. However, some natural antioxidants of the oil are removed during it,so it's recommended to store oils in form of crude oil.
6, The thermal decomposition occurs mostly in the peroxide bleaching process. It is easy to form peroxide and decomposition during the bleaching process mixed with air (such as bleaching in air), which catalyzes chain reaction, the peroxide value of long storage decolorized oil will rise. Decomposition of volatile and non-volatile molecular fragments present in the bleaching oil, so anisidine value increases. Therefore, bleaching is usually carried out under vacuum conditions to control the occurrence of peroxide.
7, The deodorizing decomposes the peroxide residues and removes small molecule compositions to lower the anisidine value, if the deodorizing device leaks into air , peroxidation occurs, the peroxides formed are decomposed into fragments. After deodorization effectively removes the volatile compounds of small molecular fragments, the anisidine value measured is only related to non-volatile fragment compounds,the value is also related with cumulative peroxides.Even if we can not smell and taste non-volatile compounds, but the oil quality is poor, and these fragment compounds catalyze the oil to continue rancidity.
