Development of a first order derivative spectrophotometry method to rapidly quantify protein in the presence of chitosan and its application in protein encapsulation systems

•First order derivative spectra of bovine serum albumin (BSA) solutions were measured.•Derivative absorbance at 288 nm linearly correlated with BSA concentration.•Calibration curve based on derivative absorbance showed high accuracy and sensitivity.•The calibration curve had high tolerance to chitosan and other interfering factors.•The new method proved its validity by showing high mass balance in BSA encapsulation. A new protein quantification method based on first order derivative spectrophotometry was established to eliminate various interferences, mainly chitosan, to the utmost using bovine serum albumin (BSA) as a model food protein. Absorbance spectra of BSA solutions were recorded and their first order derivative calculated. The values of derivative absorbance at 288 nm were used to generate linear calibration curve of BSA. The new method was applied in entrapping BSA into chitosan-tripolyphosphate beads. A general calibration curve was established with a CI (width of 95% confidence interval of three repeat measurements of unknown samples) less than 0.0262 g/L and a LOQ (limit of quantification) of 0.11 g/L, showing excellent tolerance to various interferences, which was further verified by the good mass balance of BSA during encapsulation. Overall, the method successfully eliminated the interferences from chitosan and other factors to facilitate the measurement of protein in complicated environments.