Abstract: Tannic acid was used to precipitate soluble proteins in fermented fishmeal.Applying a time-of-flight mass spectrometer,the molecular weight of the protein in the filtrate was found to be lower than 2047.98Da.Total solvable peptide content in the fermented fishmeal was determined by using the biuret method,and polypeptide in the precipitate by using Kjeldahl method.Then,the oligopeptide content was calculated.This determination method showed recovery rates for the 2546 Da and 1500 Da low molecular weight proteins to be 92.42% and 5.91%,respectively.

Key words: Oligopeptides, tannin, biuret method, Kjeldahl method, determination methodology