Efficient and low-damage descaling technology for tilapia based on multi-drum

Tilapia is an important species of aquaculture in China. It is widely used in aquatic product processing due to its tender meat, less bones and low price. The main products are fillet and frozen fish. Fish pre-treatment process is complex. The key links include descaling, head removal, viscera removal and cleaning, etc. Fish descaling machine refers to a kind of mechanical equipment to remove the scales of fish body by using the scale-scraping structure. It is usually used for batch processing small and medium-sized fish or processing large fish one by one. Descaling machine can use the methods including water jet, scraper, brush, mesh-plates, etc. The descaling machine can be divided into intermittent type and continuous type according to the feeding mode. The roller structure is one of the effective methods for fish descaling. Scraper, mesh-plate and other structural parts are installed in the inner wall of the drum. Descaling is realized under the interaction between the fish body and the inner wall of the drum while the drum is rotating. Compared with water jet, roller descaling has the characteristics of large handling capacity and good continuity of production. In the actual production, the final production effect will be affected by the type of structural parts, the structure of the drum and the actual production operation. This paper focuses on exploring the practical effect and influencing factors of different components in the process of drum descaling. Four common descaling structures are selected such as steel mesh, punched mesh, angle cutter and rebar. A drum descaling experimental device was designed to carry out the research on the technological parameters of the tilapia drum descaling. The descaling rate and damage degree were measured under different test conditions. On this basis, a multi-drum descaling device was designed and tested. The results show that: Descaling time and drum speed are the main parameters affecting the descaling effect of expanded metal lath and punched mesh. The descaling rates with different descaling time were significantly different (P < 0.05), and the descaling rates increased with the increase of time. The descaling rate can reach 95% when the drum speed is 35 r/min and the descaling time is close to 4 min. Descaling effect of angle steel cutter at different drum speeds is significantly different (P < 0.05). The descaling rate can reach up to 90% when the drum speed is about 35 r/min. Thus it can be seen that angle steel cutter suitable for fish descaling processing onalarge scale. The resulting damage is significantly increased, although increasing the tool angle can improve the descaling effect. The descaling effect of rebar at different drum speeds is significantly different (P < 0.05). The descaling rate increases with the increase of rotating speed. The descaling rate can reach up to 90% when the drum speed is increased to 55 r/min. The damage of fish body mainly includes mouth damage, fin damage, surface scratch and other types. The damage degree increased with the increase of descaling time. The optimum parameters of tilapia drum descaling device are 35 r/min and 3 min. According to the descaling effect, expanded metal lath and punched mesh were selected to form a multi-drum descaling device. Under the experimental conditions, the descaling rate was up to 95% after 3 min of processing, and the damage was low. The combination of different descaling functional parts can effectively improve the descaling effect and reduce the damage. This study obtained the best roller descaling process parameters used for tilapia. It provides the basis for the improvement and optimization of tilapia drum descaling equipment.