This is our fifth blog post in our continuing series on the analysis of milk and dairy products. (Previous posts were on accelerated solvent extraction (ASE) of the total fat in dairy products, ion chromatography (IC) analysis of iodide in milk products, nitrite and nitrates in milk products, and determination of leather protein adulteration in milk.)
Why do manufacturers enrich infant formulas with sialic acids? It is because sialic acids play an important role in immune system and cognitive development in infants. Here is an excellent article, The role and potential of sialic acid in human nutrition, published in the European Journal of Clinical Nutrition on this subject.
Many neuraminic acids have been identified in human milk: N-acetylneuraminic acid (Neu5Ac) is predominant, while N-glycolylneuraminic acid (Neu5Gc) is generally absent. Bovine milk is different, containing about 5% Neu5Gc, different forms of sialic acids, and less than 25% of the total sialic acid content compared to human milk. Unfortified infant formula from bovine milk will, therefore, be lower in sialic acid content and have different sialic acid proportions compared to human milk. Because of the critical role these carbohydrates play in infant development, many manufacturers enrich infant formulas with sialic acids to more closely mimic human milk. Sialic acid determination in a complex matrix, such as a dairy product, presents many challenges.
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Application Note 266, Determination of Sialic Acids Using UHPLC with Fluorescence Detection, (downloadable PDF) addresses these challenges and how to solve them. In this work, N-acetylated sialic acids are determined and O-acetylated sialic acids are identified by HPLC with fluorescence detection in infant formula samples in 20 min as compared to the common 40 min isocratic method. The method uses a fast liquid chromatography analytical column (Thermo Scientific Dionex Acclaim RSLC 120 C18 column) that allows fast run times and requires less acetonitrile than other published methods by using a lower flow rate and having a shorter run time. The sensitivity of fluorescence detection easily allows determination of sialic acids in the infant formula which are present in the pmol range.
Let us know of your testing challenges in milk and dairy products in the comment box below. We look forward to hearing from you!