| Shell color changes from dark blue to bright orange when crustacean is cooked. It wasdue to the release of carotenoids when the crustacyanin was heated. Main researches of thisphenomenon are focusing on the structure change, especially the interaction of carotenoidsin the crustacyanin during heating. However, the relationship between shell color changeand the physicochemical properties of crustacyanin has rarely been studied.There is a high production of Litopenaeus vannamei, as known as white leg shrimp, inChina, and cooking was the most common consumption way. Shell color not only mastersthe consumption choice, but also reflects the quality of shrimp. Meanwhile, there were fewresearches focused on the heating conditions and shell color change. In this paper, wechose the white leg shrimp as the material, and the optimal extraction of β crustacyaninfrom the shell and its physicochemical properties and the relationships between βcrustacyanin and shell color were investigated. Main tasks and conclusions of the paper areas follows:(1) The optimal extraction and characterization of β crustacyanin from the shrimpshell. The traditional method including two main steps: first, extract the crude protein byammonium sulfate precipitation from the shell; second, obtain the purified β crustacyaninvia HPLC (Mono Q column). A new extraction method, pH shifting was used to comparewith the traditional one. According to the results, The material，with a molecular mass of75000Da and λmax580nm consists of carotenoprotein and carotenoids, mainly exists in αhelix form and contains more than60%α helices. Iso-electric point was5.6. The maximumsolubility of β crustacyanin by using pH-shifting were60.5%(pH3.0) and55.7%(pH11.0), respectively. The recovery ratio was47.5%at pH3.0,20%higher than traditional.λmaxshowed no differences via two methods.(2) Effects of pH (3-11), temperature (25-100℃), heating time (1-90min), salts(0.1-5.0mol/L) and alcohol (10-70%) on the secondary structure of β crustacyanin. Theresults showed that β crustacyanin owned a stable pH from6to8, with no significant αhelix content (p>0.05). And the content decreased significantly (p<0.05) while out of thisrange, the lowest value was25.5%(pH5.0). The lost of α helix turned to random coil. αhelix decreased significantly (p<0.05) within the increasing of temperature, there was aintermediate state during60-70℃, peak denaturation was reached when heating over80 ℃, the lost of α helix also turned to random coil. α helix decreased significantly (p<0.05)during extend heating time under low temperature (<60℃), and no significant effect(p>0.05) under high temperature (>80℃). At room temperature, α helix can be induced by0.1mol/L of NaCl, due to the lost of α helix content, high NaCl concentration caused anirreversible denaturation of β crustacyanin. After heating, the NaCl triggered an inverselyproportional acceleration to β crustacyanin. The lost of α helix turned to β sheet when heatbelow40℃, and turned to β form over60℃. Induction and inhibition of trifluoroethanoland methonal had significant effect on α helix (p<0.05). The induced and inhibited abilitieswere positively related with the concentration of alcohol. Increasing of α helix wastransferred from random coil, while the decreased helicals were turned to β sheet.(3) Effects of pH (3.6-6.6), temperature (40-100℃), heating time (1-20min) andsaline concentration (0.1-4.0mol/L) on β crustacyanin and shell color change. Shell color(L and a) increased significantly (p<0.05) within the increasing of pHs, the highest Huntervalues were obtained at pH5.6. Temperature has a significant increasing effect (p<0.05) onshell color. Shell color L value increased within adding time, while a value has asignificant decreasing trend (p<0.05). And shell color decreased significantly (p<0.05) withadded salts. Orthogonal test showed the best parameters for shell color were: temperature,80℃, saline concentration2.0mol/L, pH3.6and heating time1min. |
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