Abstract:

Bicinchoninic acid (BCA) method was used for determining protein content in milk and compared with Kjeldahl method. Meanwhile, the resistance of BCA method to interference of urea, a nitrogen-containing interferer, was analyzed. Results showed that an average absorbance at 562 nm wavelength was obtained in precision test of BCA method, and the standard deviation was 0.004. Spike recoveries at two levels of protein determined by BCA method were within the range of 98.00%－ 103.00%. In 6 replicated experiments, average values of protein content in 50- and 100-fold diluted milk were determined to be 791.2 and 803.4 μg/mL by BCA method and 370.2 and 384.0 μg/mL by Kjeldahl method, respectively. Experiments on urea interference revealed RSDs below and over 5% for protein determinations by BCA and Kjeldahl methods, respectively. As a conclusion, BCA method has the advantages of simplicity and good reliability, stability and resistance to urea interference, thereby providing an attractive alternative to Kjeldahl method for protein determination.

Key words: protein content, BCA method, milk, urea, interference, Kjeldahl method