Study Of Polyphosphate Hydrolysis Of Frozen Tilapia Muscle And Non-phosphate Additive

1. An ion chromatography method was applied for determine polyphosphate hydrolysis in frozen Tilapia muscle. The changes of the water holding capacity, Ca2+-ATPase activity and -SH content of myofibrillar protein caused by polyphosphate hydrolysis were measured. Results are as follows: orthophosphate (Pi), pyrophosphate (PPi) and tripolyphosphate (TPP) were separated completely by ion chromatography method. During the frozen storage, TPP was firstly hydrolyzed to PPi and Pi, and PPi was further hydrolyzed to Pi in the frozen Tilapia muscle. Meantime, PPi was hydrolyzed directly to Pi; The hydrolysis of TSPP and STPP affected its influence on the properties of frozen Tilapia. In this study, STPP was hydrolyzed to PPi and Pi quickly at the beginning, increased the water holding capacity (WHC). The highest WHC was detected at 7 d in the frozen storage, with TSPP 84.0% and STPP 81.6%,higher than control (70.91%); Pyrophosphate has the significant function of enhancing the water-holding capacity of meat food , and its hydrolysis weakened this function, resulted in protein denaturation, then Ca2+-ATPase activity declined as the frozen storage processed; Samples treated by TSPP had higher content of–SH than that of STPP, indicated polyphosphate hydrolysis affected the properties of frozen Tilapia muscle significantly.2. The effects of polyphosphates on the microstructure of Tilapia myofibrillar were studied. The mechanism of PPi on water holding capacity was described as: enabled the myofibrilar lattices expand laterally; increased the space of I- band by extracting protein from both ends of A-band; increased the space of A-band by extracting protein from H-band; destroyed the juncture of the myosin and actin by the energy liberated from the hydrolysis of chemical bond. The mechanism of TPP was described as: enabled the myofibrilar lattices expand laterally; increased the soluble protein content by the ion strength; firstly hydrolyzed to PPi, which effectively destroyed the structure of myofibrillar. HMP could chelate metal ion that affected the hydrolysis of PPi and TPP. As a result, the function of PPi and TPP was modified.3. A safe effective phosphate alternative was exploited. The product from sodium alginate depolymerized by HCl could significantly increase the weight of white leg shrimp and decreased the frozen drip loss. Marinating in the solution of 0.5% depolymerized sodium alginate, the weight of white leg shrimp has increased to 11.5%, and decreased the frozen drip loss, retained the tenderness of the shrimp. Further research has revealed that product from sodium alginate depolymerized 10h by HCl at 60℃which has a molecular mass of 6000kDa could increase the weight of Tilapia fillet , as well as decreased the frozen drip loss.