Degradation of polyphosphates during the manufacturing process of surimi-based products - Effect of magnesium concentration on enzymatic degradation

Abstract

The effect of magnesium (Mg) concentration on the degradation of polyphosphates (PP) in salted meat paste (SMP) during the setting process has been investigated. Surimi was prepared from minced walleye pollack muscle by washing twice with a buffer solution (pH 7.5). The SMPs, which were mixtures of surimi, NaCl, tripolyphosphate (P3), pyrophosphate (P2) and various concentrations of Mg, were incubated at 20°C for 0~20 hr. Amounts of P3 and P2 remaining in SMP were measured. While P3 was completely degraded within about 8 hr, regardless of Mg concentration (3~13 mmol/kg), P2 degradation was dependent on Mg concentration in SMP. P2 was hardly degraded in the presence of 3 mmol/kg Mg for 20 hr, but was completely degraded at 13 mmol/kg Mg for 8 hr. The effect of Mg on pyrophosphatase (P2ase) and tripolyphosphatase (P3ase) activities has been investigated at various concentrations of P2 and P3. The relation between activity and Mg concentration was hyperbolic for P3ase and sigmoid for P2ase. Both P3ase and P2ase activities were saturated at Mg concentrations higher than the P3 and P2 concentrations. Moreover, P2ase activity decreased with increasing P2 concentration below 3 mmol/kg Mg. It was presumed that these differences in Mg concentration dependence of P2ase and P3ase are relevant to the degradation rate of PP in SMP. On the other hand, the gel strength of SMP was recognized to increase in the presence of Mg at a concentration sufficient to form Mg-PP complex. Therefore, it is suggested that increase of Mg concentration in SMP not only accelerates P2 degradation, but also enhances gel strength.