DETERMINATION OF TOTAL PROTEIN CONTENT IN ROYAL JELLY: A COMPARISON OF THE KJELDAHL, THE BRADFORD AND THE LOWRY METHODS

Crenguţa-Ioana Pavel, L.Al. Mărghitaş, Victoriţa Bonta, Cristina M. Mihai, Lavinia I. Tomoş

Abstract
The bee products gained lots of popularity as healthy food nowadays. Protein content is an recognized parameter used for the quality evaluation of royal jelly. A comparative study of the Kjeldahl and two specrophotometric methods (Bradford and Lowry) was carried out in order to find the most relevant assay for total protein determination on pure royal jelly samples. The protein values obtained by Kjeldahl and Lowry methods were significant different. The Kjeldahl method showed higher protein values and lowest variation of protein content in royal jelly than Bradford and Lowry methods. Both the Bradford and Lowry methods had a higher sensitivity than Kjeldahl method and equivalent variability (standard deviation about the means). The results showed that all three assays can be used for protein analyze in royal jelly, but Bradford method provide more reliable protein values than Kjeldahl method and even than Lowry method due to a higher sensitivity and precision. In a context of lack of standard methos for evaluating royal jelly composition, this study is very useful for the control laboratories food and bee-products quality.

Key words: Protein analysis, Kleldahl method, Bradford method, Lowry method, Royal jelly