Proteins reaction with lactose

The MaiUard reaction of lactose and proteins in mUk has long been investigated mainly from a view point of nutritional quaUty of pasteurized and powdered miUc or mUk products (2). AvaUability of an essential amino acid, lysine, is decreased by the reaction with lactose during heating for pasteurization and spray-drying for powdering of milk. Loss of avaUable lysine and production of reaction interm ates are estimated by amino acid analysis of acid hydrolysates of milk samples. 

M. Pischetsrieder, C. Schoetter, and T. Severin, Formation of an aminoreductone during the Maillard reaction of lactose with V-acetyllysine or proteins,. /. Agric. Food Chem., 1998, 46, 928-931. 

Hill, R.D. and Laing, R.R., Specific reaction of dansyl chloride with one lysine residue in rennin, Biochim. Biophys. Acta 132, 188-190, 1967 Chen, R.F., Huorescent protein-dye conjugates. I. Heterogeneity of sites on serum albumin labeled by dansyl chloride. Arch. Biochem. Biophys. 128, 163-175, 1968 Chen, R.F., Dansyl-labeled protein modified with dansyl chloride activity effects and fluorescence properties. Anal Biochem. 25, 412M16, 1968 Brown, C.S. and Cunningham, L.W., Reaction of reactive sulfydryl groups of creatine kinase with dansyl chloride. Biochemistry 9, 3878-3885, 1970 Hsieh, W.T. and Matthews, K.S., Lactose repressor protein modified with dansyl chloride activity effects and fluorescence properties. 

Glycation has been observed in a lyophilized formulation of relaxin in which a glucose adduct was identified.Formulation of recombinant human DNase with lactose in a spray-dried state resulted in the addition of lactose molecules to five of the six Lys in the protein.A similar reaction was observed in a lyophilized formulation of hGH in lactose. Because of the tendency of reducing sugars to undergo the Maillard reaction with proteins, they are not the carbohydrates of choice for use in formulations. 

The concept of coupling reaction with membrane separation has been applied to biological processes since the seventies. Membrane bioreactors (MBR) have been extensively studied, and today many are in industrial use worldwide. MBR development was a natural outcome of the extensive utilization membranes had found in the food and pharmaceutical industries. The dairy industry, in particular, has been a pioneer in the use of microfiltra-tion (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) membranes. Applications include the processing of various natural fluids (milk, blood, fruit juices, etc.), the concentration of proteins from milk, and the separation of whey fractions, including lactose, proteins, minerals, and fats. These processes are typically performed at low temperature and pressure conditions making use of commercial membranes. 

As far as food products are concerned, the most important and obvious consequences of the Maillard reaction are the development of color and flavor. These effects may or may not be desirable, but they are always accompanied by a decrease in the nutritional value of proteins. In milk for instance, the reaction of lactose with... 

Food intolerances are mostly caused by substances other than proteins and affect a limited number of individuals. Examples include sulfite-induced asthma, lactose intolerance, MSG-induced headache and flushing, etc., yet these substances are only associated with these symptoms and remain unproven as causative agents. Significant levels of these non-flavor ingredients are typically required to elicit this type of reaction, and there is no evidence that flavoring substances are involved (Taylor and Dormedy, 1998). 

F g- 13.13 Principle of protein crosslinking by enzymatic oxidation of lactose coupled with the Maillard reaction [35-37]. 

This enzyme [EC 2.4.1.22] is a protein complex of two proteins (designated A and B) and catalyzes the reaction of UDP-galactose with D-glucose to generate UDP and lactose. In the absence of the ce-lactalbumin (protein B), the enzyme catalyzes the transfer of galactose from UDP-galactose to A-acetylglucosamine (Le., the activity of A-acetyllactosamine synthase, EC 2.4.1.90). 

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