Process optimization of roller extruder with equal diameter of antarctic krill

Antarctic krill had enormous quantity in the Southern Ocean and great value of development and utilization. However pretreatment processing such as husking of Antarctic krill was more difficult than other main economic shrimps because Antarctic krill was smaller and the fishing area was far from land. The whole machining process of Antarctic krill was finished on the ocean-going ships. The research of pretreatment technology of shrimps developed later in China. Peeling method was studied in order to get integral meat of Antarctic krill. Parameters such as body length and weight of the Antarctic krill just be caught up were measured. The sample which had a body length between 40mm to 45mm was selected and be kept fresh. The krill was peeled by manual and mechanical operation respectively and the meat yield of the sample was measured. Considering the effect of shear and rub produced by differential rotation and effect of squeeze produced by relative rotation, dual rollers were designed in constant velocity and relative rotation in order to keep the meat integrally. Taking the roller diameter 50mm as the fixed parameters in the test, the impacts of roller speed, roller gap and the number of rotation on peeling were researched. The process conditions of roller extruder of Antarctic krill were optimized by Box-Behnken center-united experiment design. Taking meat yield as dependent variable, the models were obtained by using response surface analysis of the three factors of roller speed, roller gap and the number of rotations based on single factor experiments. The results indicated that interaction effect of roller speed and roller gap on the meat yield achieved very significant level. The influencing factors had a complicated relationship with each other. Among these factors roller gap had the most significant impact on the meat yield, roller speed and the number of rotations ranked in order. The optimized technology parameters were that roller speed was 1.6 rolls per second, the roller gap was 0.5 mm and the number of rotations was 1.7r, respectively. Under the optimized conditions the meat yield was 36.44%. The experiment indicated that there was a good fit between the predicted and the experimental values. The mathematical model was also very accurate. Therefore, the peeling process conditions getting from the response surface for Antarctic krill had a certain value in use and the method would probably be used on the ship. Then the relationship between the storage time of krill and the meat yield was studied. The results showed that: the meat yield of peeling continuous decrease with the increase of storage time. The meat yield by manual husking reduced from 35.29% to 29.73% and the meat yield by machine reduced from 34.71% to 21.08%. Mechanical manipulation got lower meat yield than the manual operation and the decline was more apparent. Meat of krill might easier be squished in peeling by machine and caused the reducing of the meat yield. This phenomenon was more obviously under poor quality. The result provided the reference for the development of peeling equipment of Antarctic krill.