Determination of Total Protein Content in Milk Powders: a Comparative Study of the Kjeldahl, Lowry and Bradford Method

Wong, Pui Munn (2017) Determination of Total Protein Content in Milk Powders: a Comparative Study of the Kjeldahl, Lowry and Bradford Method. Final Year Project (Bachelor), Tunku Abdul Rahman University College.

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Abstract

Protein content is a recognized parameter used for the quality evaluation of milk powder. In the present study, a comparative study of the Kjeldahl and two spectrophotometric methods, the Lowry and Bradford method were carried out in order to find the most appropriate assay for total protein determination in a range of milk powder samples (Anlene, Dutch Lady, Everyday, Fernleaf, Nespray). The protein values obtained by Kjeldahl, Lowry and Bradford methods were significantly different. The Kjeldahl method showed more accurate protein values and the smallest variation of protein content in milk powder than both the Lowry and Bradford method. Both Lowry and Bradford method showed a higher sensitivity than Kjeldahl method but Bradford method is slightly more sensitive than Lowry method and it has a larger variability (standard deviation about the means) than both Kjeldahl and Lowry method. The results showed that all the assays studied can be used for protein analysis in milk powder, but Kjeldahl method provide more reliable protein values than both Lowry and Bradford method due to its high accuracy, precision and good reproducibility. Kjeldahl method is still preferred since the spectrophotometric ii methods can only perform the determination of soluble protein in a sample and the quantification of insoluble protein is still being determined by Kjeldahl analysis.