Acta Scientiarum Polonorum Technologia Alimentaria

Background. Microbial milk-clotting enzymes are valued as calf rennet substitutes in the cheese industry. The worldwide increase of cheese production coupled with a reduced supply of calf rennet has prompted a search for calf rennet substitutes, including microbial and plant rennets. However, most plant rennets have proved unsuitable because they impart a bitter taste to the cheese. Microbial rennet appears to be more promising because its production is cheaper, biochemical diversity is greater, and genetic modifi cation is easier. Most cheese manufacturing facilities in Egypt perform land spreading of salt whey. However, this practice increases the chloride levels of soil, and elevates the risk of crop damage. One possible application for salt whey is to use it as a whole medium for growth and production of milk clotting enzyme from fungi.

Material and methods. Mucor pusillus QM 436 was identifi ed to produce the highest milk-clotting activity during screening of 19 fungal strains. Salted whey results from Ras (Cephalotyre) cheese manufacture as a whole medium for growth of Mucor pusillus QM 436 and production of the enzyme.

Results. The milk-clotting enzyme from Mucor pusillus QM 436 was purifi ed to 7.14-fold with 54.4% recovery by precipitation in ammonium sulfate, ethanol and fractionated by gel fi ltration on Sephadex G-100. The enzyme was active in the pH range 5.5-7.5 and was inactivated completely by heating 5 min at 70°C and 30 min at 65°C. The highest level of enzyme activity was obtained at 60°C, pH 5.5. A positive and proportional relationship occurred in the presence of CaCl2 in milk, with inhibition which occurred in the presence of NaCl.
Conclusions. The high level of milk-clotting activity coupled with a low level of thermal stability suggested that the milk-clotting enzyme from Mucor pusillus QM 436 should be considered as a potential substitute for calf rennet.