Cathepsin D activity in quarg

Quarg cheese was produced from raw skim milk, pasteurised skim milk, raw sk im milk with rennet added and ultrafiltrated raw skim milk. Quarg was also produced from raw skim milk with pepstatin added at curd cutting and from u ltrafiltration retentate of raw milk with added pepstatin. No starter bacte ria were used in this model system, with the reduction of pH being achieved by addition of glucono-delta -lactone. Yields ranged between 20.25 and 23. 5%, with protein levels of 13.6-15.7%. Proteolysis occurred during storage of all experimental cheese samples For 3 m at 8 degreesC. By immunoblotting using antibodies against bovine cathepsin D, immunoreactive procathepsin D was identified in all cheese samples. Presence of cathepsin D or procathep sin D-derived activity was confirmed by a specific enzyme assay in all samp les, except those which contained pepstatin. Inhibition of cathepsin D-cata lysed proteolysis by pepstatin was observed in chromatograms of water-solub le extracts analysed by reverse-phase HPLC. Peptides thought to be produced as a result of cathepsin D activity were observed in cheese made from both raw and pasteurised milk, suggesting that the activity at least partially survived pasteurisation. (C) 2000 Elsevier Science Ltd. All rights reserved .