Study On The Stability Of Polyunsaturated Fatty Acids In The Infant Milk

Lipid oxidation causes quality,deterioration during manufacture and storage of lipid-containing foods.In the peroxidation of unsaturated fatty acids,lipid hydroperoxides are formed during the propagation phase.These primary compounds are unstable and rapidly decompose in the presence of trace elements to give a range of compounds,including alkoxyl and alkyl radicals,aldehydes,ketones and a range of carboxyl compounds that form acomplex mixture of secondary lipid oxidation products,which spoil infant formula(IF) milk powders.When stored,infant formula milk powders are usually protected from light and maintained at room temperature. However,because of the long storage life of these powders(usually 2 years),PUFAs can be oxidised,giving rise to a loss of nutritive value and to the generation of volatile compounds from peroxides.Therefore,milk products such as infant formula milk powders,once opened,are highly susceptible to lipid oxidation at room temperature,and light will accelerate this process.Traditionally,the peroxide value (POV) has been used to determine primary lipid oxidation products.The higher the POV is,the weaker the plant oils are.At present,the microencapsulation technology is usually used for embedding of PUFA in order to slow down the oxidation of PUFA in the majority of infant formula products all over the world.However,due to the different quality of microcapsules technology and oil,the stability and the product's shelf-life of oil are different too.In addition,many products are added natural antioxidants to prolong the shelf-life. However,the analysis of fatty acid composition to extend the preservation of PUFA has not been reported.Polyunsaturated fatty acids are like to be oxidative,degenerative and inactivate. To maintain the stability of PUFA,We study systematically from the food system,the main componet of the food,environmental factors and various types of functional fatty acid.Then we can use these rules to improve the storage stability and shelf-life of the high PUFA products.The fatty acid compositions of the rapeseed,soybean,peanut,sunflower,tea, blend,corn and sesame oil were analyzed by gas chromatography.The effects of the temperature on the oxidation of plant oils were studied by Schall oven test according to POV and fatty acid composition.The relationship of the POV and fatty acid composition was studied by Matlab.Based on our laboratory results of the Chinese breast-feeding survey,The PUFA ratio and formulation of the IF milk powers which are fit to our Chinese infant and child was studied in this paper.At the same time,the paper gave some useful suggestions on the short shelf life of PUFA.The results are shown as followed:1.The oxidative stability from strong to weak was as followed:peanut,tea, sesame,rapeseed,corn,blend,soybean and sunflower oil;2.The oxidative stability of the oils was greatly affected by temperature.The effect of Cu²⁺ was greater than Fe³⁺;3.Few changes were observed in the fatty acid content during storage.There was a reduction in PUFA and an increase in SFA and MUFA.Moreover,the reduction of n-3PUFA was more obviously than n-6PUFA.But significant losses were found in long chain fatty acids sush as C16:0,9cC18:1,C22:3n-3 and C20:4n-6.And small increase could be found in short chain fatty acids.There were the same change trend in different vegetable oils,complex oil and microcapsules of products;4.The relationship models of the POV and fatty acid composition were eatablished preliminarily under the oxidization conditions.And we can generally predict the POV of different oils through the fatty acid composition;5.The bigger the PUFA and n-3/n-6PUFA was,the poorer the oxidation stability of the oil was;6.Microencapsulation could effectively improve the oxidation stability of plant oil,and the external environment was very important to the stability of infant formula milk powder.