Auto oxidation of unsaturated lipids in emulsions
Unsaturated Lipids: Unsaturated lipids are the lipids which have one or more double bonds between carbon atoms. Emulsion: An emulsion is a colloid of two or more immiscible liquids where one liquid contains a dispersion of the other liquids. Autoxidation: Autoxidation is a form of oxidation in which lipids and oxygen are involved, it doesn’t involves light and catalyst.
Problems related to autoxidation Oxidation of lipids is undesirable It causes rancidity, off falvour,bad taste in foods, effects appearance. Decreases nutritive value. Deterioration of food. Effects shelf life and limits the use of unsaturated lipids in food application.
Diseases related to oxidation Inflammation Auto immune disease Cardiovascular disease and also leads to aging.
Mechanism of autoxidation Autoxidation is a spontaneous reaction of oxygen with lipids leading to oxidative deterioration and processed by three radical chain mechanism involving three steps. Initially per oxides are formed which may break down into secondary oxidation products(hydrocarbon,ketones,aldehyde etc.) Presence of metals even in small amount in lipid can also promote autoxidation.
Mechanism of autoxidation.
Factors affecting Lipid oxidation in food emulsion: Chemical structure of lipid Oxygen concentration Antioxidants Temperature Surface area Water contents etc.
Emulsion is divided into three region: Oil in the interior side of emulsion droplet Interfacial material between lipid and aqueous phase And aqueous phase itself.
Increasing oxidative stability and droplet size Addition of protein in the emulsion increases the oxidative stability. Oxidation increase as the droplet size decreases providing more surface area or oxygen to react with Encapsulating unsaturated fatty acids with polysaccharides could retard oxidation.
Determination of Autoxidation By Peroxide Value determination: Peroxide value directly measures the concentration of hydro peroxide formed in the first step By iron thio cyanate Method: Its is spectrophotometric method that is based on ability of peroxides to oxidize ferrous ion than ammonium thio cyanate solution is added which forms Iron three thiocyanate. Content of hydroperoxiadation can be obtained through colorimetry.
Conjugated Dienes Value: Ultra violet spectrophotometry method is used to detect lipid oxidation containing or generating conjugated unsaturation. Active Oxygen Method: This method is used to predict the stability of lipids bubbling through a solution of the lipids using specific flow rate, temperature and concentration. High performance liquid Chromatography(HPLC): HPLC is used to determine lipid peroxide present . Infra red spectroscopy: This method detects the major products of lipid oxidation like lipid hydroxyl and hydroxyl groups.
How to Control !!! Using antioxidants Proper regulation of temperature Protection from light, aeration and moisture Vacuum packaging Inactivation of enzymes