Utilization of fish processing by-products for nutritional formulation of fish feed

by Maghaydah, Sofyan.

Maghaydah Sofyan S. (Writer) (Last Name) (First) (Initial) Utilization of Fish Processing By-Products for Nutritional Formulation of Fish Feed (Title) Food & Nutritional Sciences Gour Choudhury May/2003 55 (Graduate Major) (Research Advisor) (Month/Year) (No. of Pages) APA (Name of Style Manual Used in this Study) Small-scale fish farms market roughly 50 percent of the farm production. Processing of fish to produce fillets yields an immense quantity of underutilized byproducts. Depending on the species, 30 to 80 percent by weight of the fish is not utilized for direct human consumption and is discarded as by-products or waste. For example, in a typical trout processing operation the finished trout fillet yield is approximately 50 percent of live weight. By-products consisting of trimmings, heads, frames, fins, skin, and viscera are as high in protein as the fillet and are disposed of as waste. Such disposal creates environmental problems and is a loss of valuable nutrients. This study was an attempt to develop a low-cost farm technology for production of fish feed pellets utilizing trout processing by-products. The process consisted of five unit operations: thermal processing, grinding, mixing, extrusion, and drying. Pretreatment requirements (heating time and temperature) to produce fish slurry with no microbial load were determined. iii Cooked fish by-products were ground to reduce the particle size of the softened bones and to create a smooth slurry. Nutrient amendment requirements were established by proximate analysis (moisture, fat, protein, and minerals) of the fish slurry to meet the dietary requirements of trout. The by-products and supplementary ingredients were mixed and then extruded through a specially designed die using a Hobart meat grinding attachment. The pellets were dried using a forced-convection drier. The response variables evaluated during process development were aerobic and anaerobic plate counts, pathogenic bacteria, apparent density, floating time, and sinking velocity. The raw by-products had a high aerobic (6.7x105-5.7x106 CFU/g) and anaerobic (3.3x104- 6.5x105 CFU/g) load with no pathogens. Thermal processing at 121°C and 131x103 Pa for 15 minutes was sufficient to destroy microbial populations and soften the bones of the raw by-products. A subsequent grinding was needed for production of a smooth slurry; grinding time ranged from 12 to 17 minutes. Proximate analysis conducted on the by-products indicated that the fish slurry needed supplementation with protein, lipid, minerals, and vitamins to meet the dietary requirements of trout. The byproducts and supplementary dry ingredients were mixed using a Hobart mixer at a low speed for 15 minutes into an extrudable dough. A 50 mm-long multi-channel die provided enough pressure for pelletizing. The die had 10 openings (4.5 mm each) distributed around the circumference. The fish feed pellets were dried to approximately 5 percent moisture using a conventional oven for 45 to 49 minutes to impart structural integrity, shelf-life, and water stability to the pellets. The apparent density of the fish pellets (1.1x102 kg/m3) was higher than that of water, which resulted in fish, feed pellets that sank. More research is needed to optimize the technology and scale up the process. iv The process developed can be applied to small scale processing of by-products from other fish species leading to full utilization of cultured fish. In addition, this resource recovery system eliminates solid waste disposal problems. Such a technology can potentially benefit fish farmers everywhere in the country and the world. v To my teacher... Gour Choudhury vi