<![CDATA[Protein quantification in complex biological samples remains challenging due to their heterogeneous composition. This study aimed to compare direct UV absorbance at 280 nm (A280) and the bicinchoninic acid (BCA) method for protein quantification of dialyzed Cosmos caudatus crude protein extract. Crude protein extract was prepared from Cosmos caudatus leaves, followed by ammonium sulfate fractionation (45%, 65%, 85%, and 95%) and dialysis using a 3.5 kDa membrane. Protein concentration was measured using a NanoDrop spectrophotometer (A280) and BCA assay, with measurements performed in triplicate. Relative standard deviation was used to evaluate the variability among triplicate measurements. Data were analyzed using paired t-test after Shapiro-Wilk normality testing. Results showed that protein concentrations obtained by A280 were consistently higher than those measured by the BCA method, with values approximately 3.24-5.36 times greater across all fractions (p<0.001). The observed differences may be associated with the distinct measurement principles of the two methods, the contribution of UV-absorbing compounds and the dependence of A280 measurements on aromatic amino acid residues. In conclusion, A280 and BCA methods produced significantly different protein concentrations and should not be used interchangeably for quantifying dialyzed crude plant protein extract.]]>
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