Abstract: Protein content in crude polysaccharide extract isolated from Acaudina molpadioides was determined comparatively by four commonly used protein quantification methods, i.e., Lowry, bicinchoninic acid, Bradford and fluorescence spectrometric methods in order to find out an accurate and simply method for quantifying protein in the matrix. It was calculated on the basis of amino acid composition that the crude extract contained (5.06 ± 0.31)% of protein, which served as a benchmark for the comparison among protein quantification methods. Lowry, bicinchoninic acid fluorescence spectrometric methods gave protein contents of (4.92 ± 0.20)%, (6.29 ± 0.51)% and (3.88 ± 0.25)%, respectively, while no protein was detected by Bradford method. The comparative results show that Lowry method is the most accurate method among the four quantification methods. Moreover, the method has the other characteristics of good reproducibility, short time consumption, simplicity and low requirements for analytical instruments and equipments.

Key words: sea cucumber, Acaudina molpadioides polysaccharide, glycosaminoglycan, protein quantification, Lowry methodmethod