Mechanism of Polyphosphates Hydrolysis by Purified Polyphosphatases from the Dorsal Muscle of Silver Carp (Hypophthalmichthys Molitrix) as Detected by ³¹P NMR.

The dynamic hydrolysis of tetrasodium pyrophosphate (TSPP), sodium tripolyphosphate (STPP) and polyphosphate compound, which was catalyzed by purified pyrophosphatase (PPase) and myosin- tripolyphosphatase (TPPase) from the silver carp dorsal muscle, was studied using (31) P NMR spectroscopy. In the PPase + TSPP system, the pyrophosphate (PP) was hydrolyzed quickly and completely within 8 h and the hydrolysis rate of PP was 12.51%/h. In the TPPase + STPP system, the first-order hydrolysis of tripolyphosphate (TPP) was not yet complete after 48 h, and the derived PP accumulated progressively. Given the coexistence of PPase and TPPase, only 1.20% of TPP in STPP alone remained after 48 h. However, the generation rate of Pi in the polyphosphate compound (TSPP: STPP: sodium hexametaphosphate = 1: 8: 1) was 0.76%/h, which was less than 0.88%/h in STPP alone. In the presence of polyphosphatases, the decrease of PP or TPP content in the polyphosphate compound was not as rapid as that in TSPP or STPP alone due to the inhibitory effect of PP on TPPase and the effect of low system pH on PPase. The understanding of polyphosphates hydrolysis mechanism was capable of developing the advanced polyphosphate mixture in order to reduce the phosphate residue in fish products. Processors appreciate the proven value of phosphates to increase the yield and functionality of the fish meat products. Our studies showed that the hydrolysis rate of PP or TPP in the blend was slower than that of polyphosphate alone. Thus, it is likely that the addition of PP and TPP in a polyphosphate blend had a prolonged interaction with proteins in fish meat processing and the effectiveness of polyphosphates was enhanced.