Studies on the nitrogen recovery in enzymic hydrolysis of Atlantic salmon (Salmo salar, L.) frames by Protamex ™ protease

In three consecutive experiments, frames without heads from Atlantic salmon were hydrolysed by Protamex ™ protease. In experiment I (24 factorial design) nitrogen recoveries (NR) of 44–76 % were obtained, after 120 min of hydrolysis, by systematically varying the hydrolysing parameters, starting pH (5.4–7.7), temperature (36–50 °C), E:S ratio (30–90 AU kg−1 crude protein) and frames–water ratio (0.71–1.21) between low and high levels. The highest levels of E:S ratio (90 AU kg−1 crude protein), temperature (50 °C) and starting pH (7.7) and the lowest level of frames–water ratio (0.71) resulted in the highest NR (76%). In experiment II, the optimal temperature and starting pH in the hydrolysis with Protamex ™ were established at 50–56 °C and 6.5–7.6, respectively. Beyond these temperature and starting pH intervals, the NR tended to decrease. In experiment III, at optimal temperature (50 °C) and starting pH (6.5) conditions and frames–water ratio of 1.2, NR of 43–61 % were achieved after 60 min of hydrolysis, by varying the E:S ratios from 10–90 AU kg−1 crude protein. The highest E:S ratio resulted in the highest NR but running the hydrolysis for a period longer than 60 min resulted in little increase in NR. © 2002 Elsevier Science Ltd. All rights reserved