Proteolytic degradation of cold-water fish gelatin solutions and gels.

The stability of cold-water fish gelatin (FG), both in solution and in the gel phase, has been studied as function of both temperature and exposure towards novel proteases of marine origin. A 1% (w/v) FG solution was readily degraded by such proteases above 20 degrees C, which was expected since FG at this temperature is a random coil molecule lacking the protective triple helical structure found in collagen. The dynamic storage modulus for a 10% (w/v) FG gel increased monotonically at 4 degrees C. Ramping the temperature to 6, 8 or 10 degrees C led to a drastic reduction in G', but an apparent partial recovery of the network (increasing G') was observed with time at all temperatures. In the presence of proteases, a lower storage modulus was observed. At constant 4 degrees C, an apparent maximum value was reached after curing for 2h followed by a decrease in G' indicating protease activity. Ramping of temperature in the presence of proteases led to an even more drastic reduction in G' and no recovery of structure was observed with time. In this case, the overall rheological behaviour is a complex function of both thermal influence as well as proteolytic activity. In an endeavour to quantify the effect of the presence of proteolytic enzymes on the gelatin network, rheological investigation were undertaken where the dynamic storage moduli were recorded on different 10% (w/v) FG samples that had been acid hydrolysed to yield different average molecular weights. A significant reduction in storage modulus for average molecular weights below 50 kDa was found. This critical molecular weight most probably reflects the on-set of a regime where shorter chain lengths prevent percolation due to an increase in the loose end and sol fraction as well as a reduction in the average length of the pyrrolidine-rich regions reducing the number of possible junction zones.

Proteolytic activity and protease classes in the zooplankton species Calanus finmarchicus.

The temperature optimum for the general proteolytic activity in the crude extract of Calanus finmarchicus was 50 degrees C and the pH optimum was found to be 7. The use of specific protease inhibitors resulted in the identification of at least three protease classes in the crude extract of C. finmarchicus. Those classes were serine, metallo and aspartic proteases. The serine and metallo proteases were found to be dominant under neutral to alkaline conditions and the aspartic proteases were dominant under acidic conditions. The cysteine proteases, if at all present, did not seem to be active or present in any substantial amount. The data presented points towards controlling and preserving the protein content in fresh C. finmarchicus.