Optimisation of activity and storage stability of crude pepsin extracted from adult cattle Abomasa for cheese making

Abstract

The study conducted to investigate the activity and storage stability of crude pepsin extract for use as rennet substitute in cheese processing. The conditions tested were regions of the abomasa, fresh versus dry abomasa drying methods, maceration temperatures (37^oC, 24-28^oC or 15^oC);  maceration pH 1-6 for 6 days; activation pH (pH 1-4) and clarification by centrifugation or use of chemicals. The shelf life of the extract was evaluated under storage temperatures ranging from deep freezing at -20^oC refrigeration temperatures (<10 ^oC) and room temperature. Results showed that fundic region of the abomasa had 70.8% pepsin while the pyloric region had only 27% pepsin. Milk clotting activity (MCA) was 1978 and 1800 pepsin units per ml (PU/ml)  for sun and shade-dried abomasa respectively. Concentrations of 5, 10, 15, 20, 25% NaCl gave 1845, 2189, 1596, 1021, 462 MCA respectively. Maceration at pH 3 for 3 days at 37 ^oC gave the highest enzymatic activity (5536 PU/ml). Clearing of the extract by centrifugation at 3000g/15 min gave an extract with 902.3 PU/ml. Clarification by use of di-sodium phosphate (Na₂HSO₄) gave extract of 1679.1 PU/ml. The enzyme activity of the extract stored under  deep  freezer temperature was sibnificantly higher (p < 0.05) than ambient and refrigeration temperatures. However, they were significantly lower (p< 0. 001) than the activity of the extract before storage. Therefore, the best pepsin extraction conditions were found to be the use of fundic region of sundried abomasa, macerated at 37^oC in an extraction solution containing 5-10% salt at pH 3 for 3 days and clarified after activation at pH2 for 20 min followed by centrifugation of sediment at 3000g/15 min or by use of anhydrous disodium phosphate. The clarified extract could retain its activity for 16 weeks when stored at - 20^oC in single use portions.

Keywords: milk, clotting activity, pepsin, rennet, abomasa, cheese

Tanzania J. Agric. Sc. (2001)Vol. 4 No l, 29-36