Lactose, occurrence

Natural Occurrence of ( — )-proto-Quercitol. Although the dextrorotatory form (12) of proto-quercitol was discovered in acorns more than a century ago by Braconnot (5), who at first thought that it was lactose, the levorotatory form (13) remained unknown until 1961. In that year, Plouvier isolated it from leaves of the tree Eucalyptus populnea the yield was 0.55% (36). The optical rotation of the new compound was equal and opposite to that of the dextro enantiomer, and it was identical to the latter in its crystal form, melting point, solubilities, molecular formula and infrared spectrum. 

A review of medical research has led to the conclusion that ethnic differences concerning lactose intolerance are largely genetic in origin. A culture historical hypothesis has been offered to explain the present-day occurrence of various Old World groups with high and low incidences of lactose intolerance based on milk use (Simoons 1981). It is currently believed that the decline in lactase activity with age is determined by an autosomal recessive gene and is not influenced by the amount of lactose consumed. 

Lactose intolerance can be readily managed by ensuring that the amount of lactose ingested is restricted to the amount the individual can tolerate, which is related to the individual s level of residual intestinal lactase activity. Lactose maldigesters can determine their individual threshold for the occurrence of lactose intoler-... 

We open with a brief report of the early discovery of the occurrence and isolation of these proteins and the elucidation of their function and homology, followed by a brief discussion of some problems in their isolation and the determination of their activity. We then consider various aspects of their three-dimensional structures and their significance. We summarize studies on the implications of their sequence similarities, and also on the binding of metal ions, especially calcium(H), and consider their implications. Then follows a brief discussion of lactose synthase, an enzyme of which a-lactalbumin and galactosyltransferase are essential components. We then examine the evidence concerning the evolution of the two proteins, about which there are conflicting views (see Section X,B). Some conclusions and predictions of future directions are made. 

The only mammal for which the presence of lactose in its milk has not been reported appears to be the California sea lion (Jenness, 1982). No nonmammalian occurrence of a-lactalbumin has been reported. 

Different localized levels of molecular order can coexist in some pharmaceutical materials, giving rise to the occurrence of partially crystalline (and partially amorphous ) systems. In most cases, the properties of such materials (e.g., density) are intermediate to those of the 100% amorphous and 100% crystalline samples. By deliberately varying the level of crystallinity in such systems, their properties can be customized for a particular purpose. An example of this is with the tableting excipients microcrystalline cellulose and spray-dried lactose, which have had their compression characteristics optimized by manipulating their amorphous content. The properties of partially crystalline materials may be approximated in many instances by making physical mixtures of the totally amorphous and crystalline samples. This is known as the two-state model for partially crystalline systems.However, such experiments should be undertaken with caution as the mixed two-state material can sometimes have significantly different properties from the partially crystalline material that is manufactured directly (the real one-state system). ... 

Cooking starch in the presence of amino acids may favour the occurrence of Maillard reactions, lowering the bioavailability of lysine in the diet. 13C CPMAS was used to follow the effect of Maillard reactions on the bioavailability of potato starch.124 A loss of crystallinity was found for the three samples studied starch, amylopectin, and amylose, being more marked for amylose. A similar study on chestnut starch indicated that Maillard reactions do not influence significantly its digestibility.125 NMR was used to characterize some Maillard reaction products extracted from model reactive mixtures such as starch-glucose-lysine 126 and lactose-lysine.127... 

The occurrence of rather high levels of lactic acid together with high levels of lactose might indicate that the laetie acid has been added to the butter. Together with the inoculation of butter to obtain cultured butter, often lactic acid is added (see Scheme 1). Also it mi t have been added for flavour or as a preservative. 

Occurrence. Found in the milk of all mammals to the extent of approximately 5%. It has been reported that a methanol extract of the longstyled pollen of forsythia flowers contains lactose (61). 

Citric acid (1.8 g/1) is the predominant organic acid in milk. During storage it disappears rapidly as a result of the action of bacteria. Other acids (lactic, acetic) are degradation products of lactose. The occurrence of orotic acid (73 mg/1), an intermediary product in biosynthesis of pyrimidine nucleotides, is specific for milk ... 

In agreement with the occurrence of Neu5Gc in colostrum and milk oligosaccharides from bovine and porcine sources, transfer from CMP-Neu5Gc to lactose could be demonstrated (Bartholomew et al. 1973, Carlson et al. 1973 a). 

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