Lactulose milk product

Figure 2.19 Concentration of lactulose in heated milk products (modified from Andrews, 1989).

Adachi, S. and Patton, S. 1961. Presence and significance of lactulose in milk products A review. J. Dairy Sci. 44, 1375-1393. 

Sec also Carbohydrates and Milk and Milk Products. LACTULOSE. See Sweeteners. 

Another lactose heat-derived compound is lactulose (4-0-6-D-galactopyranosyl-D-fructofuranose) which was first reported by Montgomery and Hudson (37). This compound can be found in heated milk products, heat processed lactose-containing foods, and alkaline lactose solutions via the isomerization of lactose. It is of interest due to claimed beneficial effects on the gut flora of infants. It has also been proposed as an indicator of the severity of heat treatment in processed dairy products (5). Apparently, it can be present in two forms in heated milks, namely in free solution and covalently bound to protein amino groups. 

Separation of these two carbohydrates is of great importance both for the dairy industry and for clinical analysis. In milk products, for example, a failure in the pasteurization process can force lactose to isomerize to lactulose due to heating. Because lactulose is not metabolized and ingestion of large amounts of lactulose can produce diarrhea [227], the lactulose content in milk products is a quality feature for a perfect pasteurization. The fact that lactulose cannot be metabolized makes it valuable in clinical applications. If lactulose is administered to a patient, kidney permeability can be examined via the urinary excretion rate. 

Separation of these two carbohydrates is of great importance for the dairy industry as well as for clinical analysis. In milk products, for example, a failure in the pasteurization process can force lactose to isomerize to lactulose due to heating. 

Lactulose is found in heated milk products. It is a little sweeter and clearly more soluble than lactose. For example, condensed milk contains up to 1% of lactulose, corresponding to an isomerization of ca. 10% of the lactose present. The formation proceeds via the Lobry de Bruyn-van Ekenstein rearrangement (cf. 4.2.4.3.2) or via SchiffhasQ. Traces of epilactose (4-0-P-D-glacto-... 

Kuncewicz. A., Panfil-Kuncewicz, H. and Michalak, J. (2000). Lactulose and furosine as indices of the degree of heating of milk and other food products, Przemysl Spozywczy, 5, 20-22. 

Data from Table I point out that other milk-based products are likely to form Amadori products, in this case lactulose-lysine and fructose-lysine, even under moderate thermal treatments. The furosine content, originating from the acid hydrolysis of Amadori products, was high in a whipping agent made from sugar and Na caseinate. It is surprising, however, that cheeses have also relatively high furosine levels. 

Thiazolium salt XTT has been used to evaluate the extent of the Maillard reaction in UHT (ultra-high-temperature)-treated milk, where it proved more rapid and convenient than determination of lactulose, HMF, or furosine.451 To establish the nature of the Maillard reaction products (MRP) involved, the interaction of the aminoreductone from lactose and n-butylamine (Amax = 319.5 nm) with MRP was studied. Excellent correlation (r = 0.967, n = 19) was found between the increased absorbance at 319.5 nm and XTT reducibility, as measured at 492 nm, near Alliax for the formazan, the reduction product of XTT. 

Ammonium hydroxide at 37° isomerize.s lactose to lactulose (32) and, in common with alkalis, causcjs fragmentation to give D-galactose (34) and its isomerization products (36), together with other substances in which D-lyxose and imidazole derivatives were tentatively identified. Lactulose and D-tagatose (D-/yxo-hexulose) have been detected in heated milk. <... 

Lactulose p-D-Galp-(1 4)-D-Fruf Milk, diary products ... 

In dairy products also hydroxymethylfurfural (HMF) and lactulose are common markers. For the determination of HMF, which also results from the Maillard condensation (18), precursors of browning products in milk are transformed to HMF after addition of oxalic acid and following heating (79). Principally, the HMF value of a milk can be used as an indicator for the heating process, but data from literature offer a wide range for this value which suspect that the HMF determination is insufficiently reproducible between laboratories. In particular, the level of HMF in untreated material, measured during the determination of "total HMF" and subtracted from the levels in treated milks, is a source of variation (20). However a comparison between the furosine and the HMF-method demonstrated the usefulness of the HMF-method as a rapid and simple measure of heat damage caused by the UHT process (77). 

Dehydrated milk-based foods is the major source of D-lactulose-amino acids in human nutrition. The dairy industry widely uses milk dehydration to manufacture powdered milk as a base for numerous dairy products, such as infant formulas, confectionaries, reconstituted milk etc. During the process of heating, drying and storage, lactose in milk can readily interact with amino compounds that are naturally present, primarily lysine residues in milk proteins. Estimated contents of D-lactulose-amino acids in selected products are compiled in Table 2. Commercial dairy products may contain, therefore, up to 40% of protein lysine in form of lactulose-lysine. Dietary availability of D-lactulose-amino acids is similar to that of the fructosamine derivatives. An ample evidence exists that the Amadori-type lysine glycoconjugates are not available to mammals as a nutrient and that lactulose-lysine is partially absorbed into the bloodstream and excreted unchanged. ... 

Lactulose (P-Gal/>-(l—>4)-Fru is a semi-synthetic disaccharide composed of fructose and galactose resulting from the alkaline isomerization of lactose. This disaccharide is present in significant concentrations in some food products since the isomerization can occur naturally, as for example, during heat treatment of milk (Barreteau et al., 2006). However, the isomerization reaction has several drawbacks, and the steps required for the separation and purification of these products presents high costs and results in low yields of lactulose. Several studies have investigated viability of biological production of lactulose by enzymes (Kimetal., 2005). 

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