Screening and isolation of milk-clotting enzymes from seaweed

Abstract

Cheese-making involves milk coagulation as a crucial step where calf rennet has been used traditionally as the milk-clotting enzyme in the cheese industry. This study investigated milk-clotting enzymes from seven species of seaweed and evaluated the parameters for their isolation and partial purification including post-harvest processing, extraction and purification methods. The saturation degree of ammonium sulphate and the precipitation stages were evaluated to obtain optimal purification conditions, and three desalting methods, namely dialysis, desalting column and the combination of dialysis and desalting column, were investigated to determine the most suitable method for ammonium sulphate removal. Protein extracts of all seven species of seaweeds exhibited some caseinolytic activity, but the extract of unprocessed (whole) dried samples had higher protein yields and stronger caseinolytic activities. The extract from one species, Gracilaria edulis, demonstrated the ability to clot milk. The evaluation of the purification method for G. edulis extract revealed an optimum single step of 50% saturation and ammonium sulphate precipitation with dialysis as the desalting method.