Application of the inhibition ELISA method to the study of proteolysis caused by heat-resistant Pseudomonas proteinases specific towards kappa-casein in heated milk

An investigation was undertaken to demonstrate that the residual enzymic activity of a pure psychrotrophic proteolytic strain on kappa-casein induced the gelation occurring in milk after an ultra-high-temperature (UHT) process. A strain of Pseudomonas fluorescens was added to pasteurized milk. Then, different thermal treatments (pasteurization, UHT processing) were applied to this milk. the UHT milk was stored at different temperatures. The hydrolysis of kappa-casein was determined by the detection of caseinomacropeptide (CMP) by an enzyme-linked immunosorbent assay (ELISA) method. At every step, determinations of proteolysis and proteolytic potential were realized. Before pasteurization and after inoculation, the milk had a proteolytic potential of 18.5 mu g CMP/ml. Then, the corresponding UHT treated milk was destabilized by heating after 2 d storage at 37 degrees C and exhibited a proteolysis of kappa-casein approximate to 25%, i,e. 250 mu g CMP/ml. The UHT milk stored al 20 degrees C was destabilized after 14 d and contained about the same CMP concentration.