A Preliminary Study On The Formation And Control Of White Particles In Shaoxing Sufu

White particles in sufu are one of the problems affecting the qualities of sufu appearance. In this paper, the white particles in Shaoxing sufu, including their components, tyrosine changes during fermentation and the ways to control white particles were studied.The components of white particles in Shaoxing sufu, including amino acids and proteins, were analyzed using high-performance liquid chromatography, N-tris(hydroxymethyl) glycine- sodium dodecyl sulfate-polyacrylamide gel electrophoresis(Tricine-SDS-PAGE) and matrix-assisted laser desorption ionisation-time of flight/time of flight mass spectrometry(MALDI-TOF/TOF MS). The results showed that tyrosine is the major constituent of white particles, accounting for 76.62% of the total amino acids. Proteins in white particles were identified as basic polypeptide B1 b of soy Glycinin G1 with the molecular weight of 25.4 k Da.Nitrogen containing materials in pehtze and soup of sufu with and without white particles were compared. It was found that white particles containing sufu had larger amounts of amino nitrogen, free amino acids, trichloroacetic acid nitrogen soluble index(TCA-NSI), degree of hydrolysis(DH) and free tyrosine in pehtze. Furthermore, the secondary structure of proteins in the soup of sufu was investigated by fourier transform infrared spectrometer(FTIR). There was more α-helix and less β-sheet in proteins in the soup of white particles containing sufu.At the same time, the hydrolysis of proteins and free tyrosine during fermentation process of Shaoxing sufu were researched as well as the enzymatic properties of tyrosine carboxypeptidase. Results showed that free tyrosine increased as increase of amino nitrogen, TCA-NSI, free amino acids and DH in pehtze during Shaoxing sufu fermentation. It was found that extra Zn2+ enhanced protease activity and thus the free tyrosine contents were increased, while acetic acid inhibit the activity of protease resulting in reduced free tyrosine. The tyrosine carboxypeptidase showed thermal stability at 25~45oC and p H stability at p H 5.0~8.0. Its activity was affected by Na Cl and ethanol existed in soup of sufu.The present study tried to control white particles of Shaoxing sufu by adding Tween 80 and inactivate protease, with white particles reduced by 50% and 8.3%, respectively.