Chemistry Reference
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90
85
40°C
80
30°C
75
20°C
70
10°C
65
0°C
60
0
10 20 30 40 50 60 70 80 90 100
% Invert of total sugars
Figure 2.15
Solubility curves for sucrose-invert sugar mixtures at various temperatures. The dotted line
shows peak solubility composition for various temperatures. (Adapted from Davis, P. R. and
Prince, R. N.,
Liquid Sugar in the Food Industry
. Copyright 1955, American Chemical Society.)
andsolubility,canformhighlyconcentratedsolutionsofhighosmolality(BeMillerandWhistler
1996).
Lactose
:Itisasugarthatoccursalmostonlyinthemilkofmammals.Lactoseiscomposedof
two differentsugar residues:d-glucose and d-galactose linked viaβ-(1→4)-linkage (Figure 2.16;
Izydorczyk2005).Itcanoccurintwoisomericcrystallineforms,theα-hydrateandtheβ-anhydrous,
andcanbefoundinanamorphousorglassystate;α-lactoseisthemostcommonformandcanbe
obtainedbycrystallizationfromasupersaturatedsolutionbelow93.5°C,whileβ-lactosebycrys-
tallizationabove93.5°C(Figure2.17).Bothformsexhibitmutarotationwithinalspeciicoptical
rotation
[
= +
.Lactosesolutionsseekastateofequilibriumbetweentheαandβforms.At
roomtemperature,theequilibriumresultsinaratioofabout40%α-lactoseand60%β-lactose.The
factthattwoformsoflactoseexistwithdifferentmolecularstructurehasprofoundeffectsonvari-
ouspropertiesoflactose,suchasitssolidstateproperties,crystalmorphology,andsolubility(Fox
2009).LactosereducesFehling'ssolutionandishydrolyzedbyacidorenzymaticallytoglucoseand
galactose.
Lactose in mammals is enzymatically hydrolyzed in the small intestine by β-galactosidase.
Lactose intolerance/malabsorption relates to the inadequate level ofβ-galactosidase to hydrolyze
α
20
]
55 3
.
CH
2
OH
CH
2
OH
O
O
H
OH
OH
H
H
O
OH
H
H
H
H
H
H
OH
H
HO
Figure 2.16
Structure of lactose.
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