Study On The Technological Process Of Frozen Roasted Channel Catfish

The channel catfish products in our country are mostly semi-finished products, which is mainly exported. The exportation was influenced by international market competition and trade barriers. The frozen prepared channel catfish product were studied in this thesis in order to expand the domestic market. The products made from channel catfish product is safe and nutrient, for its high fat content and no intermuscular bone, while channel catfish has earthy smell and get splintery during cooking. The study aims to cover the earthy smell by the processing of deodorization and roasting, and prevent the fillets from crazing by proper drying, providing the possibility of producing frozen prepared channel catfish products with convenience, nutrient-rich and good flavor. The experiments concentrated on the slaughter method of channel catfish, the processing of product and the preservation characteristics of product, providing theoretical guidance for the scale standardized production of frozen and roasted channel catfish fillet.Four slaughtering methods, carbon dioxide narcosis, electrical treatment, percussion and bleeding in ice slurry, were compared in order to assess their suitability as slaughtering methods for frozen channel catfish fillet stored in refrigerator of-18 oC. Muscle p H, color, haemoglobin content, drip loss, TVB-N and bacterial counts were considered for this study. Muscle p H values change were relatively slighter in bleeding in ice slurry and percussion group over a 45-hour period, a drastic change were found in the carbon dioxide narcosis group. Fish bleeding in ice slurry was significantly brighter than other three groups, as indicated by significant lower a* values and higher L* values, and the haemoglobin content were also significantly lower. The drip loss of fish slaughtered by percussion was significantly lower than those slaughtered according to other methods throughout the entire storage time(60 days). The bleeding in ice slurry group has a significant lower TVB-N value, while no significant difference was observed between the other three groups. The results indicated that slaughter by bleeding in ice slurry and percussion improved the quality of frozen channel catfish fillet.Sensory quality was used as an indicator to determine the deodorization of five kinds of materials, which including red tea, purple perilla, extraction of licorice root, cooking wine and yeast, the results showed that the cooking wine has a better deodorization effect than other materials and it would be best when the cooking wine content was 30%. The salt concentration and pickling time was studied by using salt content and sensory quality as indicator, the product could have a better taste when the fish block was pickled by 3% salting concentration for 2.5 h.The optimal drying condition was concluded by evaluating the texture and fat oxidation, the drying temperature was about 50 oC and moisture content of 75%. The denaturation temperature of protein was detected by differential scanning calorimeter(DSC), indicating that the central temperature of fish block must be arrived at 75 oC by roasting. The effect of different roasting conditions on fat content, moisture content, fat oxidation, volatile compounds, color and texture were studied, it turns out that the optimal roasting condition were 200 oC for 7 min, the products roasted by this condition has a better quality in the aspect of moisture content, texture, fat oxidation and volatile compounds.The condiment was prepared with sugar, cooking wine and soy sauce, the soluble solid content was determined as 35%, the mixed ratio as sugar: soy sauce: cooking wine=15:3:4, mainly based on the sensory evaluation. The products has a better flavor and texture when roasted with condiment 3 times at the condition of 200 oC for 4 min.By measuring sensory scores and physicochemical indicators during a 300 days of the frozen storage, the results showed that p H values and TBARS didn’t change dramatically. The aerobic plate count was lower than the aquatic product hygiene standards. The TVB-N value increased while far lower than the standards during the whole storage period. The sensory scores decreased, the shelf life was recommended as 6 months considering the acceptability of sensory quality. It was found that products before and after frozen has no significant difference by a sensory difference test.