Lactoperoxidase, milk

Lactoperoxidase Milk (not human milk), saliva, tears Anti-microbial effects (viruses, bacteria, fungi, parasites, myco-plasms)... 

Fonteh F A, Grandison A S and Lewis M J (2002), Variations of lactoperoxidase activity and thiocyanate content in cows and goats milk throughout lactation , Journal of Dairy Research, 69, 401 -09. 

Peroxidases have also been utilized for preparative-scale oxidations of aromatic hydrocarbons. Procedures have been optimized for hydroxylation of l-tyrosine, D-(-)-p-hydroxyphenylglycine, and L-phenylalanine by oxygen, di-hydroxyfumaric acid, and horseradish peroxidase (89). Lactoperoxidase from bovine milk and yeast cytochrome c peroxidase will also catalyze such hydroxylation reactions (89). 

The lactoperoxidase system produces various compounds for antimicrobial protection of milk, the principal one of which is hypothiocyanite (OCNS ) as a result of the lactoperoxidase-catalyzed oxidation of thiocyanate (SCN ) by H2O2. No overheating should take place during the pasteurization process, to avoid damaging lactoperoxidase . 

As indices of the thermal history of milk alkaline phosphatase, y-glutamyl transpeptidase, lactoperoxidase. 

Antimicrobial activity lysozyme, lactoperoxidase (which is exploited as a component of the lactoperoxidase - H202 - thiocyanate system for the cold pasteurization of milk). 

With a few exceptions (e.g. lysozyme and lactoperoxidase), the indigenous milk enzymes do not have a beneficial effect on the nutritional or organoleptic attributes of milk, and hence their destruction by heat is one of the objectives of many dairy processes. 

The occurrence of a peroxidase, lactoperoxidase (LPO), in milk was recognized as early as 1881. It is one of the most heat-stable enzymes in milk its destruction was used as an index of flash pasteurization (now very rarely used) and is now used as an index of super-HTST pasteurization. 

Since the principal constituents of milk are proteins, lipids and lactose, proteinases, lipases and / -galactosidase (lactase) are the principal exogenous enzymes used in dairy technology. Apart from these, there are, at present, only minor applications for glucose oxidase, catalase, superoxide dismutase and lysozyme. Lactoperoxidase, xanthine oxidase and sulphydryl oxidase might also be included, although at present the indigenous form of these enzymes is exploited. 

Bjorck, L. (1993) Indigenous enzymes in milk Lactoperoxidase, in Advanced Dairy Chemistry, Vol. 1 Proteins, (ed. P.F. Fox), Elsevier Applied Science, London, pp. 332-9. 

Bjorck, L. and Claesson, O. 1979. Xanthine oxidase as a source of hydrogen peroxide for the lactoperoxidase system in milk. J. Dairy Sci. 62, 1211-1215. 

Small amounts of hydrogen peroxide in raw milk can activate the lactoperoxidase-catalyzed oxidation of thiocyanate to produce a bacterial inhibitor (Hogg and Jago 1970). Inhibitory compounds resulting from oxygen metabolism can produce initially slow starter culture growth in industrial dairy fermentations if the milk has been excessively agitated. 

The human body contains lactoperoxidase, a product of exocrine secretion into milk, saliva, tears, etc., and peroxidases with specialized functions in saliva, the thyroid, eosinophils,219 and neutrophils.220 The functions are largely protective but the enzymes also participate in biosynthesis. Mammalian peroxidases have heme covalently linked to the proteins, as indicated in Fig. 16-12 220 222a... 

Griffiths (2) studied the thermal stability of the naturally occurring enzymes in milk at temperatures between 65 and 80°C, in order to choose an enzymatic index of adequate pasteurization of milk. For the acid phosphatase, the D-values of 7.38 min at 75°C and 7.87 min at 80°C corresponded to a z-value of 6.6°C for the inactivation of lactoperoxidase, D-values of 0.80 min at 75°C and 0.075 min at 80°C corresponded to a z-value of 5.4°C for amylase (saccharifying activity), D-values of 0.85 min at 75°C and 0.45 min at 80°C corresponded to a z-value of 16.2°C. The naturally occurring enzymes in milk showed lower D-values than those found for GFPuv in the three buffers. However, a z-value of 16.64°C characterized for GFPuv in phosphate buffer solutions at pH 7.0 was similar to that obtained for amylase in milk. 

Bjorck, L. 1978. Antibacterial effect of the lactoperoxidase system on psychrotrophic bacteria in milk. J. Dairy Res. 45, 109-118. 

Carmen, M., Hernandez, M., van Markwijk, B.W., and Vreeman, H.J. 1990. Isolation and properties of lactoperoxidase from bovine milk. Neth. Milk Dairy J. 44, 213-221. 

Korhonen, H. 1980. A new method for preserving raw milk—the lactoperoxidase antibacterial system. World Animal Rev. 35, 23-29. 

Reiter, B., Marshall, V.M.E., Bjorck, L., and Rosen, C.G. 1976. Nonspecific bactericidal activity of the lactoperoxidase-thiocyanate-hydrogen peroxide system of milk against Escherichia coli and some Gram-negative pathogens. Infect. Immun. 13, 800—807. 

Uchida, T., Sato, K., Kawasaki, Y., and Dosako, S. 1996. Separation of lactoperoxidase, secretory component and lactoferrin from milk or whey with a cation exchange resin. US Patent No. 5,516,675. 

Sulphydryl oxidase, an indigenous milk enzyme, has been proposed for the oxidation of thiols in UHT milk to reduce cooked flavor and also thereby to serve as an antioxidant, in conjunction with lactoperoxidase (to destroy the resultant H2O2), by obviating pro-oxidants resulting from autoxidation of thiols (Swaisgood and Abraham, 1980). 

The mechanism(s) by which Xanthine oxidoreductase exerts its prooxidant effect(s) is not fully understood. Hydrogen peroxide, resulting from oxidation of a suitable substrate by Xanthine oxidoreductase, could oxidize milk lipids. However, normal milk contains little or no substrate for the enzyme. A possible mechanism involving interaction between native and denatured Xanthine oxidoreductase in MFGM and lactoperoxidase or copper in milk serum has been proposed (Hill, 1979 Allen and Wreiden, 1982b). 

Allen, J.C., Wrieden, W.L. 1982b. Influence of milk proteins on lipid oxidation in aqueous emulsion. II. Lactoperoxidase, lactoferrin, superoxide dismutase and Xanthine oxidore-ductase. J. Dairy Res. 42, 249-263. 

Lactoperoxidase is associated with the serum proteins of milk. It has an optimum pH of 6.8 and a molecular weight of 82,000. 

Figure 10-18 Regeneration in Ultra High Temperature Treated Milk as a Function of Storage Temperature. (A) 2°C (B) 20°C (C) 37°C. Source From F. Kiermeier and C. Kayser, Heat Inactivation of Lactoperoxidase (in German), Z Lebensm. Untersuch. Forsch., Vol. 113,1960.

---