Continuous coagulation of milk using immobilized enzymes in a fluidized‐bed reactor

Milk‐clotting enzymes such as pepsin, chymosin, chymotrypsin, and M. miehei proteases were immobilized on porous, alkylamine glass and incorporated into a fluidized‐bed continuous coagulation scheme. Only pepsin and calf rennet retained sufficient activity towards skim milk to warrant further studies. Comparison of kinetic data with fixed‐bed reactors revealed the overall superior performance of fluidized beds; higher clotting activities were possible while avoiding plugging problems and high pressure drops common to fixed‐bed reactors. Film diffusion and catalyst back‐mixing appear to be significant factors in the overall kinetics. All enzymes lost activity on exposure to skim milk. The inactivation rates were lower at high substrate pH and insignificantly affected by reactor temperature. Nitrogen and sialic acid accumulation on the porous glass paralleled the loss in activity in the initial stages. Attempts to regenerate the immobilized enzymes were partially successful.