Reactions in milk

Samuelsson (1966) concluded, on the basis of his studies, that the close proximity of a copper-protein complex to the phospholipids which are also associated with the fat globule membrane is an important consideration in the development of an oxidized flavor in fluid milks. Haase and Dunkley (1970) stated that although some aspects of catalysis of oxidative reactions in milk by copper still appear anomalous... the mechanism of oxidized flavor development with copper as catalyst involves a specific grouping of lipoprotein-metal complexes in which the spatial orientation is a critical factor. ... 

T. Henle, H. Walter, and H. Klostermeyer, Evaluation of the extent of the early Maillard-reaction in milk products by direct measurement of the Amadori-product lactuloselysine, Z. Lebensm. Unters. Forsch., 1991, 193, 119-122. 

K2. Keeney, M., and Bassette, R., Detection of intermediate compounds in the early stages of Browning reaction in milk products. ]. Dairy Set. 42, 945-960 (1959). 

Riboflavin is a potent photosensitizer and catalyses a number of oxidative reactions in milk, e.g. fatty acids, proteins (with the formation of 3-methyl thiopropanal from methionine which is responsible for light-induced off-flavour) and ascorbic acid. Milk and dairy products should be protected from light by suitable packaging and exposure to UV light should be minimized. 

In milk, as in many odier foods, oxidative reactions are a prime cause of flavor deterioration and loss in nutritional quality (1). Spontaneous oxidation in milk giving rise to oxidized flavor (off-flavor) is a well-described phenomenon (2 3), i diich is supposed to proceed dependii on factors inherent in die milk itself. These inherent factors include fatty acid conq>osition, content of low-molecular weight antioxidants, pro- and anti-oxidative enzyme systems, and transition metal ion content. Moreover, external factors such as handling, agitation, tenq>erature, exposure to light, and contamination by metals and microorganisms are known to trigger additional deteriorative oxidative reactions in milk. 

Several methods have been developed for assaying non-enzymatic glycosylation. As far as biological systems are concerned, these have been extensively reviewed by A. J. Furth in 1988 (5). They include both assays on intact proteins after chemical degradation and selective detection of e.g. 5-hydroxymethylfurfural (HMF) and formaldehyde using the thiobarbituric assay (TEA), and assays on protein hydrolysates with or without previous reduction of the protein-bound Amadori compound. In this last case, the analysis is based on the determination of furosine which is specifically formed from lysine Amadori compounds with a yield of approximately 30% (6). The furosine method, originally developed for milk (7), has been the subject of several analytical improvements both for food products (8) and biological materials (9). More recently, another method has been proposed to evaluate the extent of early Maillard reaction in milk products. This method is based on direct measurement of the Amadori product lactuloselysine which is released after complete enzymatic hydrolysis (10). 

This enzyme, sometimes also called the Schardinger enzyme, occurs in milk. It is capable of " oxidising" acetaldehyde to acetic acid, and also the purine bases xanthine and hypoxanthine to uric acid. The former reaction is not a simple direct oxidation and is assumed to take place as follows. The enzyme activates the hydrated form of the aldehyde so that it readily parts w ith two hydrogen atoms in the presence of a suitable hydrogen acceptor such as methylene-blue the latter being reduced to the colourless leuco-compound. The oxidation of certain substrates will not take place in the absence of such a hydrogen acceptor. 

Peroxidases are found in milk and in leukocytes, platelets, and other tissues involved in eicosanoid metabolism (Chapter 23). The prosthetic group is protoheme. In the reaction catalyzed by peroxidase, hydrogen peroxide is reduced at the expense of several substances that will act as electron acceptors, such as ascorbate, quinones, and cytochrome c. The reaction catalyzed by peroxidase is complex, but the overall reaction is as follows ... 

The aforementioned series of reactions provides a basis for a colorimetric analytical method for Compound 118 in which the commonly used agricultural chemicals do not interfere. The procedure described herein permits the estimation of as little as 10 micrograms of Compound 118, and has been successfully applied to the analysis of this insect toxicant in insecticidal dusts, in film residues on glass and paper, in human and animal urine, and in mixture with other insecticides. Application of this procedure to the determination of Compound 118 in milk and in spray and dust residues on plants appears promising. 

The growth of each microbe and enzyme occurs with its own unique rate. A fridge acts by cooling the food in order to slow these rates to a more manageable level. At constant temperature, the rate of each reaction equals the respective rate constant k multiplied by the concentrations of all reacting species. For example, the rate of the reaction causing milk to go off occurs between lactic acid and an enzyme. The rate of the process is written formally as... 

Iodide ion-selective electrode The iodide electrode has broad application both in the direct determination of iodide ions present in various media as well as for the determination of iodide in various compounds. It is, for example, important in the determination of iodide in milk [44,64,218, 382, 442], This electrode responds to Hg ions [150, 306, 439] and can be used for the indirect determination of oxidizing agents that react with iodide, such as 10 [305], lOi [158], Pd(II) [117, 347,405] and for the determination of the overall oxidant content, for example in the atmosphere [393], It can also be used to monitor the iodide concentration formed during the reactions of iodide with hydrogen peroxide or perborate, catalyzed by molybdenum, tungsten or vanadium ions, permitting determination of traces of these metals [12,192,193, 194, 195]. The permeability of bilayer lipid membranes for iodide can be measured using an I"... 

Lactation It is not known whether lepirudin is excreted in breast milk. Because of the potential for serious adverse reactions in nursing infants, decide whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. 

Lactation Nicotine passes freely into breast milk and has the potential for serious adverse reactions in nursing infants. 

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