Enzyme Technology
Production of syrups containing maltose
Traditionally, syrups containing maltose as a major
component have been produced by treating barley starch with barley b-amylase.
b-Amylases (1,4-a-D-glucan maltohydrolases) are exohydrolases which release
maltose from 1,4-a-linked glucans but neither bypass nor hydrolyse
1,6-a-linkages. High-maltose syrups
(40 - 50 DE, 45-60% (w/w) maltose, 2 - 7% (w/w)
glucose) tend not to crystallise, even below 0°C and are relatively
non-hygroscopic. They are used for the production of hard candy and frozen
deserts. High conversion syrups (60 - 70 DE, 30 - 37% maltose, 35 - 43% glucose, 10%
maltotriose, 15% other oligosaccharides, all by weight) resist crystallisation
above 4°C and are sweeter (Table 4.3). They are used for soft candy and in the
baking, brewing and soft drinks industries. It might be expected that b-amylase
would be used to produce maltose-rich syrups from corn starch, especially as the
combined action of b-amylase and pullulanase give almost quantitative yields of
maltose. This is not done on a significant scale nowadays because presently
available b-amylases are relatively expensive, not sufficiently temperature
stable (although some thermostable b-amylases from species of
Clostridium have
recently been reported) and are easily inhibited by copper and other heavy metal
ions. Instead fungal a-amylases, characterised by their ability to hydrolyse
maltotriose (G3) rather than maltose (G2) are employed often in combination with
glucoamylase. Presently available enzymes, however, are not totally compatible;
fungal a-amylases requiring a pH of not less than 5.0 and a reaction temperature
not exceeding 55°C.
High-maltose syrups (see Figure
4.2) are produced from
liquefied starch of around 11 DE at a concentration of 35% dry solids using
fungal a-amylase alone. Saccharification occurs over 48 h, by which time the
fungal a-amylase has lost its activity. Now that a good pullulanase is
available, it is possible to use this in combination with fungal a-amylases to
produce syrups with even higher maltose contents.
High-conversion syrups are produced using combinations of
fungal a-amylase and glucoamylase. These may be tailored to customers'
specifications by adjusting the activities of the two enzymes used but
inevitably, as glucoamylase is employed, the glucose content of the final
product will be higher than that of high-maltose syrups. The stability of
glucoamylase necessitates stopping the reaction, by heating, when the required
composition is reached. It is now possible to produce starch hydrolysates with
any DE between 1 and 100 and with virtually any composition using combinations
of bacterial a-amylases, fungal a-amylases, glucoamylase and pullulanase.
Table 4.3 The relative sweetness of food ingredients
Food ingredient
|
Relative sweetness (by weight, solids)
|
Sucrose
|
1.0
|
Glucose
|
0.7
|
Fructose
|
1.3
|
Galactose
|
0.7
|
Maltose
|
0.3
|
Lactose
|
0.2
|
Raffinose
|
0.2
|
Hydrolysed sucrose
|
1.1
|
Hydrolysed lactose
|
0.7
|
Glucose syrup 11 DE
|
<0.1
|
Glucose syrup 42 DE
|
0.3
|
Glucose syrup 97 DE
|
0.7
|
Maltose syrup 44 DE
|
0.3
|
High-conversion syrup 65 DE
|
0.5
|
HFCS (42% fructose) a
|
1.0
|
HFCS (55%
fructose)
|
1.1
|
Aspartame
|
180
|
a HFCS, high-fructose corn syrup.
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This page was established in 2004 and last updated by Martin
Chaplin on
6 August, 2014
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