BLBS102-c24 BLBS102-Simpson March 21, 2012 13:47 Trim: 276mm X 219mm Printer Name: Yet to Come
446 Part 4: MilkLactose DerivativesA number of more useful and more valuable products may be
produced from lactose (see Playne and Crittenden 2009). The
most significant are the following: Lactulose(galactosylβ-1–4fructose): A sugar not found
in nature, which is produced from lactose by heating, es-
pecially under slightly alkaline conditions. The concentra-
tion of lactulose in milk is a useful index of the severity of
the heat treatment to which milk is subjected, for example
in-container sterilisation>indirect ultra-high tempera-
ture (UHT)>direct UHT>high-temperature short-time
(HTST) pasteurisation. Lactulose is not hydrolysed by in-
testinalβ-galactosidase and enters the large intestine, where
it promotes the growth ofBifidobacteriumspp. It also has
a laxative effect and is widely used for this purpose; more
than 20,000 tonnes are produced annually.
Glucose-galactose syrups, produced by acid or enzymatic
(β-galactosidase) hydrolysis(see Chapter 25): The tech-
nology for the production of such hydrolysates has been
developed but the product is not cost-competitive with other
sugars (sucrose, glucose, glucose–fructose).
Tagatose: Is the keto analogue of galactose. It occurs at a
low level in the gum of the evergreen tree,Sterculia setig-
era,and in severely heated milk and stored milk powder.
It can be produced by treatingβ-galactosidase–hydrolysed
lactose with a weak alkali, for example Ca(OH) 2 , which
converts the galactose to tagatose, which can be purified by
demineralisation and chromatography. Tagatose is nearly
as sweet as sucrose, has a good quality taste and enhances
the flavour of other sweeteners. It is absorbed poorly from
the small intestine, serves as a probiotic and has little effect
on blood glucose; it is fermented in the lower intestine to
volatile short-chain acids that can be absorbed but provide
only approximately 35% of the energy derived from sug-
ars catabolisedviathe normal route. Tagatose has GRAS
status and is produced commercially by SweetGredients, a
company formed by Arla Foods and Nordzuker (Denmark).
Galacto-oligsaccharides:β-Galactosidase has transferase
as well as hydrolytic activity and under certain condi-
tions, the former predominates, leading to the formation
of galacto-oligosaccharides containing up to six monosac-
charides linked by glycosidic bonds that are not hydrolysed
by the enzymes secreted by the human small intestine. The
undigested oligosaccharides enter the large intestine, where
they have bifidogenic properties and are considered to have
promising food applications. These oligosaccharides are
quite distinct from the naturally occurring oligosaccharides
referred to in Section ‘Oligosaccharides’(see Ganzle 2011).
Ethanol: Is produced commercially by the fermentation of
lactose byKluyveromyces lactis.Depending on local legis-
lation, the ethanol may be used in alcoholic drinks, which
are profitable. The current interest in renewable energy
sources has created vast opportunities for lactose-derived
ethanol but its commercial success will depend on local
taxation policy.Other derivatives that have limited but potentially important
applications include lactitol, lactobionic acid, lactic acid, acetic
acid, propionic acid, lactosyl urea and single-cell proteins. Most
of these derivatives can be produced by fermentation of su-
crose, which is cheaper than lactose, or by chemical synthesis.
However, lactitol and lactobionic acids are derived specifically
from lactose and may have economic potential. Lactitol is a syn-
thetic sugar alcohol produced by reduction of lactose; it is not
metabolised by higher animals but is relatively sweet, and hence
has potential for use as a non-calorific sweetener. It has also
been reported that lactitol reduces blood cholesterol level, re-
duces sucrose absorption and is anti-carcinogenic. Lactobionic
acid has a sweet taste, which is unusual for an acid and therefore
should have some interesting applications.Nutritional Aspects of LactoseLactose is responsible for two enzyme deficiency syndromes:
lactose intolerance and galactosemia. The former is due to a
deficiency of intestinalβ-galactosidase, which is rare in infants
but common in adults, except North-Western Europeans and a
few African tribes. Since humans are unable to absorb disaccha-
rides, including lactose, from the small intestine, unhydrolysed
lactose enters the large intestine where it is fermented by bac-
teria, leading to flatulence and cramp, and to the absorption of
water from the intestinal mucosa, causing diarrhoea. These con-
ditions cause discomfort and perhaps death. Lactose intolerance
has been studied extensively since its discovery in 1959 and the
literature has been reviewed regularly (see Ingram and Swallow
2009).
The problems caused by lactose intolerance can be
avoided by:
excluding lactose-containing products from the diet, which
is the normal practice in regions of the world where lactose
intolerance is widespread;
removing lactose from milk, for example by ultrafiltration;
hydrolysis of the lactose by addingβ-galactosidase at the
factory or in the home. The technology for the produc-
tion of lactose-hydrolysed milk and dairy products is well
developed but is of commercial interest mainly for lactose-
intolerant individuals in Europe or North America. Because
the consumption of milk is very limited in South-East Asia,
the use ofβ-galactosidase is of little interest, although lac-
tose intolerance is widespread.Galactosemia is caused by the inability to catabolise galactose,
owing to a deficiency of either of two enzymes, galactokinase or
galactose-1P uridyltransferase (see Flynn 2003). A deficiency
of galactokinase leads to the accumulation of galactose that is
catabolisedviaalternative routes, one of which leads to the accu-
mulation of galactitol in various tissues, including the eye, where
it causes cataracts over a period of about 20 years. A deficiency
of galactose-1P uridyltransferase leads to abnormalities in mem-
branes of the brain and to mental retardation unless galactose is
excluded from the diet within a few weeks of birth. Both forms
of galactosemia occur at a frequency of 1 per approximately
50,000 births.