Abstract: To develop a rapid method for the determination of tilapia collagen peptide content, the colorimetric biuret method was improved using tilapia skin collagen peptide as a reference material. We determined the maximum absorption wavelength of the chromogenic complex and the concentration ranges of peptide and trichloroacetic acid (TCA) and pH for high linearity. The repeatability, precision and recovery of the improved method were tested under optimized conditions. The applicability of this method to the detection of collagen peptides from the skin and scales of tilapia with different molecular masses was also studied. The results showed that the absorbance was linearly fitted with peptide concentration ranging from 0.3 to 1.5 mg/mL under the following conditions: 13% TCA, adjustment of the system pH to 12.5, and detection wavelength 545?nm, and the following equation was obtained: y = 0.144 9 x + 0.001 5 (R2 = 0.999). The relative standard deviation (RSD) for repeatability and precision were 1.86% and 1.84%, respectively. The average spiked recoveries with and without the addition of gelatin were 113.9% and 109.7%, with RSD of 1.39% and 1.00%, respectively. The method had wide linear range, good repeatability and high accuracy. Its application to different tilapia collagen peptides showed little differences in spiked recoveries and RSD. The improved biuret method proved to be simple, rapid and suitable for the determination of peptides derived from tilapia.

Key words: tilapia, collagen peptide, colorimetric biuret method, determination of peptide content, absorbance