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Food Science and Technology International
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Isolation and Partial Characterisation of Milk-clotting Aspartic Protease from Streblus asper

S. Senthilkumar

Department of Biochemistry, University of Madras, Guindy Campus, Chennai 600025, India

D. Ramasamy

Instituteof Food and Dairy Technology, Tamil Nadu Veterinary and Animal Sciences University, Chennai 600052, India

S. Subramanian

Department of Biochemistry, University of Madras, Guindy Campus, Chennai 600025, India; subbus2020{at}yahoo.co.in

A rennin-like milk-clotting protease from the twigs of Streblus asper was purified by a factor of 65 times with 36% recovery using ethanol precipitation, ion-exchange and size-exclusion chromatographic techniques. The enzyme was found to be monomeric in nature having a molecular mass of 55kDa. The enzyme acts optimally at 55°C and was stable in the temperature range of 30–40°C. Easy enzyme inactivation by moderate heating, makes this protease extract potentially useful for cheese production. The purified enzyme is an acid protease with an optimum pH of 5.5 and it retained 96% of its residual activity between pH 5.0 and 6.0. Pepstatin A inhibited the proteinase activity, whereas iodoacetamide, phenylmethyl sulphonyl fluoride, ß-mercaptoethanol and ethylenediaminetetraacetic acid had no significant inhibitory effect suggesting the presence of aspartic acid residue at the active site. The milkclotting aspartic protease showed predominant {alpha}-helical conformation in phosphate buffer as evidenced from circular dichroic spectroscopy.

Key Words: Streblus asper • aspartic protease • milk-clotting • cheese

Food Science and Technology International, Vol. 12, No. 2, 103-109 (2006)
DOI: 10.1177/1082013206063839
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