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Effect of processing on the starch and glycemic properties of Digitaria spp.
Author(s)
Jordaan, Michelle Bernitta
Date Issued
2013
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Acha starch was isolated and purified from clean and milled acha grain.
Functional, thermal and physicochemical properties of acha starch were
analysed using appropriate methods. Wheat starch was used as the
reference standard. Acha bread from acha grain was baked and the
consumer sensory acceptability was evaluated and white wheat bread was
used as the reference standard. The effect of baking, boiling, steaming and
microwaving on the starch and glycemic properties of the acha starch was
evaluated. With regard to thermal properties, gelatinisation temperature of
acha and iburu starches typifies that of waxy starch. Acha starch has similar
retrogradation temperature profiles as that of wheat. There were however
significant differences in some of the functional properties (pasting and
turbidity) and physico-chemical properties (in vitro starch digestibility), but no
significant difference in the texture profile analysis (TPA) and water binding
capacity (WBC). WBC of both acha varieties was higher than that for wheat
starch. Due to its high break down viscosity, white acha starch can be
included in foods that are subjected to high temperature processing. This
indicates that both acha starch varieties can be used for hot and cold desserts
as well as for soft jelly like sweets and confectionery toppings. A prescreening
exercise using carboxymethyl cellulose (CMC), Xanthan gum, yeast
and acha starch as the variables was successful in concluding a recipe which
rendered acha bread with the optimum specific loaf volume for both white and
black acha bread. The optimum recipe consisted 8.0 % acha starch, 2.0 %
xanthan gum, 2.0 % CMC and 1.0 % yeast. The majority of the consumer
panellists found the crust colour, taste and aroma to be moderately desirable.
This implies that most consumers find acha bread to have the potential to be
marketed as wheat free bread. The different processing methods baking,
boiling, microwaving and steaming, affected the black and white acha starch
hydrolysis. The amount of starch hydrolysed for the different processing
methods was in the following order: baking > boiling > microwaving >
steaming. It can thus be concluded that different processing methods affects
the micro structure and physical properties of the acha and wheat samples which thus influence their starch hydrolysis. The equilibrium percentage of
starch hydrolysed after 180 min incubation was affected differently for the
various starches, black acha, white acha and wheat starch by the different
processing methods and times. In the case of baking black acha starch and
wheat bread were affected similarly. However, this was not the case for
microwaving, steaming and boiling, where both acha starch varieties and
wheat starch were affected in the same way. The rate of starch hydrolysis for
both acha varieties and wheat grain for the different processing methods,
steaming, boiling, microwaving and baking was affected to the same degree
respectively.
Functional, thermal and physicochemical properties of acha starch were
analysed using appropriate methods. Wheat starch was used as the
reference standard. Acha bread from acha grain was baked and the
consumer sensory acceptability was evaluated and white wheat bread was
used as the reference standard. The effect of baking, boiling, steaming and
microwaving on the starch and glycemic properties of the acha starch was
evaluated. With regard to thermal properties, gelatinisation temperature of
acha and iburu starches typifies that of waxy starch. Acha starch has similar
retrogradation temperature profiles as that of wheat. There were however
significant differences in some of the functional properties (pasting and
turbidity) and physico-chemical properties (in vitro starch digestibility), but no
significant difference in the texture profile analysis (TPA) and water binding
capacity (WBC). WBC of both acha varieties was higher than that for wheat
starch. Due to its high break down viscosity, white acha starch can be
included in foods that are subjected to high temperature processing. This
indicates that both acha starch varieties can be used for hot and cold desserts
as well as for soft jelly like sweets and confectionery toppings. A prescreening
exercise using carboxymethyl cellulose (CMC), Xanthan gum, yeast
and acha starch as the variables was successful in concluding a recipe which
rendered acha bread with the optimum specific loaf volume for both white and
black acha bread. The optimum recipe consisted 8.0 % acha starch, 2.0 %
xanthan gum, 2.0 % CMC and 1.0 % yeast. The majority of the consumer
panellists found the crust colour, taste and aroma to be moderately desirable.
This implies that most consumers find acha bread to have the potential to be
marketed as wheat free bread. The different processing methods baking,
boiling, microwaving and steaming, affected the black and white acha starch
hydrolysis. The amount of starch hydrolysed for the different processing
methods was in the following order: baking > boiling > microwaving >
steaming. It can thus be concluded that different processing methods affects
the micro structure and physical properties of the acha and wheat samples which thus influence their starch hydrolysis. The equilibrium percentage of
starch hydrolysed after 180 min incubation was affected differently for the
various starches, black acha, white acha and wheat starch by the different
processing methods and times. In the case of baking black acha starch and
wheat bread were affected similarly. However, this was not the case for
microwaving, steaming and boiling, where both acha starch varieties and
wheat starch were affected in the same way. The rate of starch hydrolysis for
both acha varieties and wheat grain for the different processing methods,
steaming, boiling, microwaving and baking was affected to the same degree
respectively.
Additional information
Thesis (MTech (Food Technology))--Cape Peninsula University of Technology, 2013.
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