Chemistry Reference
In-Depth Information
that bacterial α-amylase partially hydrolyzes the amylose, starch bridging the crystalline
region and protruding amylopectin branches. Starch hydrolysis decreases the rigid structure
and plasticity of starch polymers during storage. The flexibility of tortillas results from the
combined functionalities of the amylose gel and amylopectin solidifying the starch granule
during storage.
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7.8
APPLICATION OF ENZYMES IN BREAKFAST CEREALS
Ready-to-eat breakfast cereals have become well established on breakfast tables almost all
over the world. They have been defined as 'processed grain formulations suitable for human
consumption without further cooking in the home'.
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Hence, the most important raw material in any breakfast cereal is grain. Most commonly
used are corn, wheat, oats, rice and barley. Other ingredients often included in the manufac-
turing process are salt, sweeteners, flavouring agents, colouring agents, vitamins, minerals
and preservatives.
The manufacturing process of breakfast cereals involves several stages. Depending on the
type of breakfast cereal, the grain will be used in total, or may require further processing
which often includes a crushing step of the whole grain between large metal rollers in order
to remove the outer layer of bran. The whole grain or coarse grain fractions are mixed with
the rest of the raw ingredients including water, in order to be cooked to the required state.
The cooked mass will undergo a drying step to the point of achieving a soft but solid mass
which can be shaped easily, often after a tempering period which allows the grains to cool
and stabilize the moisture content of each individual grain.
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Due to advances in technology, extrusion is the most frequently used process for cooking
and for partial forming of cereal products.
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A major advantage of this technique is the ability
to achieve precise process requirements, resulting in much shorter overall processing time.
Wheat can serve as a substrate to several types of enzymes. Consequently, the use of
enzymes during the manufacturing process of ready-to-eat breakfast cereals has been known
for quite some time. Fritze
et al.
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report a process to saccharify the starch contained in
the cereal to form dextrose by enzymatic degradation using a, preferably thermostable,
α-amylase. The final product is claimed to have a good flavour and the dextrose produced
is absorbed directly as sugar by the body. However, the process includes saccharification of
the major starch content making it difficult to provide the typical matrix-forming properties
required for a cereal dough.
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Producing fructose provides a greater level of sweetness for a
given amount of starch conversion; hence more starch or high molecular weight dextrins may
be retained for their matrix forming ability and improved machinability into cereal shapes.
In 1989, Maselli
et al.
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reported the use of a glucoamylase in combination with glu-
cose isomerase and optional α-amylase in the method for making cereal products naturally
sweetened with fructose.
The glucoamylase is able to form dextrose by using the starch present in the endosperm.
Consequently, a portion of the dextrose can be converted to fructose by the use of glucose
isomerase. In combination with these enzymes, optionally, thermostable α-amylase can be
used to convert the starch to dextrins. Best results will be obtained by adding the α-amylase
prior to the addition of glucoamylase and glucose isomerase.
The amount of fructose produced by the enzymatic conversion of the starch is sufficient
to provide a sweet taste in combination with the other reducing sugars produced during the
enzymatic treatment.
