Effect on protein digestibility of different processing conditions in the production of fish meal and fish feed

The effect of processing conditions on protein digestibility and fluorodinitrobenzene (FDNB)reactive (available) lysine in the production of fish meal and extruded fish feed has been studied under pilot and commercial conditions using mink as model animals. Fish meal produced under pilot-plant conditions at processing temperatures below 70-80degreesC (FM1) had protein digestibility of 929 (grams of protein digested per 1000 g protein consumed) compared with 905 when processed at temperatures above 100degreesC (FM2). A low-temperature-processed commercial fish meal (CFM1) had protein digestibility of 940 compared with 888 for a standard commercial fish meal (CFM2). Pilot-produced extruded fish feed had protein digestibility of 913 when based on FM1 as the main protein source (95% of total protein) compared with 892 when based on FM2. Commercial extruded fish feed had protein digestibility of 912 when based on CFMI compared with 871 when based on CFM2. Varying extrusion conditions at the pilot scale, ie temperatures from 100 to 126degreesC and moisture contents from 21 to 12%, did not affect protein digestibility. Similarly, under commercial conditions, variation in temperature from 89 to 110degreesC and moisture from 24.5 to 19.5% did not affect FDNB-reactive lysine and protein digestibility. The FDNB-reactive lysine content and protein digestibility of the extruded feed were less than the values calculated from the ingredient mixture before extrusion. Thus, despite different extrusion conditions not giving different FDNB-reactive lysine and protein digestibility, the total process, ie extrusion, drying and oil coating, caused a reduction. (C) 2003 Society of Chemical Industry.