Detection and impact of protease and lipase activities in milk and milk powders

This review is an update of a previous chapter published by Ribadeau-Dumas and Grappin (1992). It mostly deals with the current and recently published techniques for analysis of protein in milk and other dairy products, as well as those that could eventually come into general use. For all these techniques, the reader will be provided with their basic principles, schematic description, instrumentation, analytical performance and references.

Quantitation of Proteins in Milk and Milk Products

Towards the classification of cheese variety and maturity on the basis of statistical analysis of proteolysis data—a review

The presence of indigenous proteolytic activity in milk has been recognized since the work of Babcock and Russel in 1897. Some early researchers attributed this activity to bacterial enzymes, but later work proved conclusively the presence of indigenous proteinases in milk. More recent research has indicated two major categories of indigenous proteolytic enzymes in milk, both originating from the animal’s blood. The major enzyme system contains plasmin, which is produced by activation of its inactive precursor, plasminogen, an event which is under the control of a complex system of inhibitors and activators. The presence of plasmin in milk and its significance to the quality of dairy products has been recognized for many decades (see Bastain and Brown, 1996, for review) and has thus been the subject of much research. However, the other indigenous proteolytic enzymes in milk, which originate from somatic cells, have been studied in detail only during the last decade. Somatic cells, the principal physiological function of which is the defence of the udder against bacterial infection, have lysosomes which contain active proteolytic enzymes, including elastase, collagenase and cathepsins B, D, G, H and L. The acid proteinase originating from somatic cells, cathepsin D, has been studied most thoroughly in milk. However, it is highly likely that the other proteinases known to be present in lysosomes are also present in milk, as has been demonstrated by the recent identification of immunoreactive cathepsin B in milk (Magboul et al., 2001) and observations of the activity of other indigenous thiol proteinases in milk. This chapter will review recent research on plasmin and its role in the quality of dairy products and will focus also on other indigenous proteinases, which have not been reviewed thoroughly elsewhere.

Indigenous Proteinases in Milk

Thermal inactivation, at temperatures between 60 o C and 140 o C, of native plasmin, plasminogen and plasminogen activators were studied in bovine milk using improved enzymatic as- says. While measured heat inactivation kinetic of plasmin and plasminogen were in line with previ- ously reported values, plasminogen activators were, surprisingly, found to be as heat sensitive as plasmin and plasminogen in a milk system containing proteins with free SH groups. Activation ener- gies (Ea) for the heat denaturation of plasmin, plasminogen and plasminogen activators were 29, 35 and 24 kJ.mol -1 , respectively, in the temperature range 95-140 o C , and 244, 230 and 241 kJ.mol -1 , respectively, in the temperature range 70-90 o C. The heat inactivation of the whole plasmin system in milk appeared to be directly influenced by the presence of β-lactoglobulin. The rate of plasmin inacti- vation during long heat treatments decreased rapidly, probably because of the disappearance of avail- able β-lactoglobulin for S-S linking. plasmin / plasminogen / plasminogen activator / heat inactivation / milk

/pdf/heat-inactivation-of-native-plasmin-plasminogen-and-55sha5wijd.pdf

Heat inactivation of native plasmin, plasminogen and plasminogen activators in bovine milk: a revisited study

Two sandwich enzyme-linked immunosorbent assays (ELISA) have been developed for quantitation of bovine milk plasminogen and plasmin. The assays used two monoclonal antibodies, one specific for plasminogen and the other specific for plasminogen plus plasmin. Plasmin concentration was obtained by subtracting the first concentration from the second. The assays were sensitive (linear range, 5–75 ng/ml), repeatable (CV, 8 and 5% for plasmin and plasminogen titration respectively), specific (no cross reactivity with the major milk proteins) and directly applicable to skimmed milk with no particular pretreatment of the sample. However, ELISA did not permit complete titration of milk plasminogen and plasmin (only 60–90% could be quantified). This lack of accuracy was due to casein interfering with the plasmin–plasminogen titration by ELISA. Results obtained with ELISA or an enzymic technique on 20 milk samples collected from individual cows milked throughout pregnancy showed that the ELISA was particularly suitable for analysis of late lactation or mastitic milk where proteinase inhibitors interfered with enzymic quantitation.

Differential titration of plasmin and plasminogen in milk using sandwich ELISA with monoclonal antibodies

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Differential titration of plasmin and plasminogen in milk using sandwich ELISA with monoclonal antibodies