Determination of N/Protein in Milk Powder by Kjeldahl Method (CAT#: STEM-EA-0044-ZJF)

Introduction

Powdered milk or dried milk is a manufactured dairy product made by removing almost all the water. This product has a far longer shelf life than liquid milk and does not need to be refrigerated, due to its low moisture content. It can be reconstituted by adding water in order to obtain a ready-to-use liquid milk: on the water addition depends the fat content, so its high nutritional quality, combined with its versatile and multi-functional properties, makes it attractive for many food applications. Dried milk is widely used as food ingredient because it is suitable for several applications: in confectionery, such as chocolate and caramel candy, manufacture of infant formula and recipes for bakery.
Kjeldahl is nowadays the most used method for determining nitrogen and protein contents in foods and feeds, thanks to the high level of precision and reproducibility and to its simple application. The modern Kjeldahl method consists in a procedure of catalytically supported mineralization of organic material in a boiling mixture of sulfuric acid and sulfate salt at digestion temperatures higher than 400 °C. During the process the organically bonded nitrogen is converted into ammonium sulfate. Alkalizing the digested solution liberates ammonia which is quantitatively steam distilled and determined by titration.