Standardization Basic Research On Identification Of Protein In Infant Formula

This paper was aimed to carry out basic research on identification of milk protein and soy protein in infant formula presently, focussing on the study of the composition of protein fractions, the mechanism of identification of two types of protein components, the establishment of identification methods and standardized evaluation studies.Firstly, the study proposed a optimization program of SDS-PAGE suitable for carrying out structural analysis of protein in infant formula:a concentration of15%separating gel, stacking gel voltage of50V, the separation gel voltage of120V, Coomassie brilliant blue staining, protein concentration of the loading sample of3-4mg/ml, sample volume of10μL, sample pre-treatment method of usage of Cazzrez reagent for protein precipitation, using Bio-Rad Quantity One software for data analysis of the electrophoresis spectrum, achieving qualitative and semi-quantitative analysis of milk protein. Simultaneously, active ingredients of milk protein in the infant formula for infants up to6months, follow-on(follow-up) formula for infants from6months to12months and toddler formula for infants from12months on were analyzed for quality evaluation by this method, the results were found that all the infant formulas samples for infants0-12months conform to the requirement of GB10765-2010National food safety standard infant formula, whose requirement of least ratio of whey protein/casein in infant formula is1.5(60:40). The infant formulas for infants up to0-6months had the most whey protein, whose ratio of whey protein/casein was between1.7and2.12(61:39-67:33), the infant formula for infants6～12months had less whey, whose ratio was between1.06and1.55(61:39-52:48), and the whey protein/casein ratio of infant formula for infant more than12months was between0.65and0.71(40:60-42:58). Although the infant formulas samples for infants0-12months conform to the requirement of GB10765-2010National food safety standard infant formula, the concentration of a-Lactalbumin (the dominant protein in human milk) is relatively low in the formula (19.1%～24.1%), whereas, a-casein, a protein not found in human milk, is between11.9%and17.8%, what’s more, it was found that the concentration of immunoglobulin (Ig) in infant formula was low. The optimized SDS-PAGE method is simple, effective, low-cost, which can be used as a standardized tool of quality evaluation in commerical supervision and quality control in dairy industries.Simultaneously, the soy protein isolated and soy-based formula were analysised using this technology, we were able to qualitative and semi-quantitative analysis of the SPI, but it was useless for soy-based formula. This is mainly due to protein of the soy-based formula was hydrolyzed to small peptides which were easily absorbed by children, what’s more, the dual protein infant formula could be qualitative and semi-quantitative analysis by SDS-PAGE. The optimized SDS-PAGE method is simple, effective, low-cost, which can be used as a standardized tool of quality evaluation in commerical supervision and quality control in dairy industries.A reversed-phase high-performance liquid chromatography (RP-HPLC) for the quantification of seven major milk proteins (κ-CN、αs2-CN、αsI-CN、α-La、 P-LgB、 P-LgA) in infant formula was developed. The recovery rate was about82%～103%and the value of relative standard deviation (RSD) was0.1%～4.9%. Compared with previous methods, the method was sensitive, accurate and rapid. In addition, the removal step of casein in albumin analysis didn’t need any more. Simultaneously, principal component analysis, cluster analysis and discriminant analysis were groundbreakingly used to identify infant formula of different functions between domestic and foreign brands, which provided a reference for quality control and quantitative analysis in infant formula.