Effects Of Compound Preservative Based On Egg Yolk Immunoglobulin Against Polyphenol Oxidase In Penaeus Vannamei

Penaeus vannamei, with the largest farming area and the maximum output in the whole world, is one of the main species of prawns in China. The production increases by7%～8%annually. High nutrition value and excellent taste make it popular among consumers. However, it may turn black and rot easily which can reduce its edible and economic value during its storage due to high-activity polyphenol oxidase in the Penaeus vannamei. The egg yolk immunoglobulin against polyphenol oxidase (PPO-IgY) can specifically inhibit the activity of polyphenol oxidase and relieve the melanosis of prawns which has been demonstrated in the previous studies. The PPO-IgY was obtained from egg yolk immunized by polyphenol oxidase. In this study, a compound preservative based on PPO-IgY,4-hexylresorcinol (4-HR) and pullulan were investigated to inhibit the melanosis and spoilage of Penaeus vannamei. Single-factor tests and multi-factor experiments were carried out according to sensory evaluation and total volatile basic nitrogen (TVB-N) detection. Main results are listed as follows:1. The inhibitions of PPO-IgY,4-HR and phytic acid on enzyme activity were first investigated. The results indicated that they all could inhibit the activity of polyphenol oxidase. Moreover, the inhibition curves were significantly in connection with the concentrations. The single-factor tests of Penaeus vannamei were conducted by sensory evaluation and TVB-N detection. The results indicated that PPO-IgY,4-HR, phytic acid and pullulan could inhibit the melanosis of prawns and prolong the shelf-life. The optimal concentration of PPO-IgY was0.5g/L,4-HR0.01-0.015g/L, pullulan5～30g/L and phytic acid0.1～1g/L. However, phytic acid was not suitable for combination with others due to its extreme acidity as it could reduce the activity of PPO-IgY and the viscosity of pullulan. Therefore, complex substances were identified as PPO-IgY,4-HR and pullulan.2. The optimal parameters of the preservative were determined as0.5g/L of PPO-IgY,0.005g/L of4-HR and10g/L of pullulan, assessed by two-step mixing experiments based on sensory evaluation and TVB-N detection. First, PPO-IgY was combined with4-HR to determine the better mixture concentrations, then different concentrations of pullulan were coated on Penaeus vannamei. Considering that soaking was more feasible than coating in practice, the two operating modes were compared based on sensory evaluation and TVB-N detection. Finally, the best treatment of compound preservative was that the Penaeus vannamei was immerged by PPO-IgY,4-HR and pullulan for15min.3. The compound preservative was applied to Penaeus vannamei and the dynamic changes of Penaeus vannamei were studied at4℃. Sensory evaluation, TVB-N and aerobic plate counts were compared between experimental and control groups. The results indicated that compound preservative based on PPO-IgY could inhibit the melanosis of Penaeus vannamei and reduce TVB-N and aerobic plate counts. The melanosis and shelf-life of Penaeus vannamei treated by compound preservative could be prolonged to the3rd and6th day, which were1day and2days later than the control groups respectively. All the results indicated that the compound preservative could be used as a safe and efficient agent applied in Penaeus vannamei preservation.