Isolation, modification and quality evaluation of starch from pearl millet varieties and development of ready-to-eat extruded snacks
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Date
2017
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CCSHAU
Abstract
The present study was carried out to evaluate the physico-chemical characteristics and functional
properties of thirteen different pearl millet varieties/hybrids to standardize the procedure for extraction and
modification of starch from pearl millet; and to evaluate the physical, chemical, functional and pasting properties
of native and modified pearl millet starch. The process for preparation of RTE extruded snacks by incorporation of
pearl millet starch was standardized using RSM. 1000 kernel weight, bulk density and swelling capacity of
different varieties of pearl millet grain ranged from 7.23-10.90 g, 0.78-0.85 g/ml and 0.004-0.006 ml/seed.
Different varieties of pearl millet contained 10.03-13.66% protein, 4.92-6.55% fat, 1.70-1.95% ash, 1.82-2.03%
crude fibre and 77.44-81.33% total carbohydrate. Yield and purity of starch extracted from different methods
ranged from 24-50% and 87.34-90.39%, respectively. On the basis of concentration of chemical used for
extraction, yield, functional properties, light transmittance, syneresis and pasting characteristics; 0.1% Na2S2O5
(T4 method) was selected for extraction of starch from different varieties of pearl millet. Yield and purity of starch
extracted from thirteen different varieties ranged from 41.6-50.5% and 88.34-90.38%, respectively. Less impurities
and high yield (50.5%) of starch was obtained from white seeded hybrid (HHB-256). Starch obtained from HHB-
256 white seeded hybrid exhibited 2.57 g/g swelling power, 2.54% solubility, 184.5% WHC; (5.7-4.4%) high light
transmittance and (0.30-2.27%) low syneresis during period of study of syneresis. Starch extracted from HHB-256
white seeded hybrid of pearl millet was used for modification using physical, chemical and enzymatic methods.
Starch modified by all the methods except pregelatinized starch (PM) showed significantly lower swelling power
(1.78 to 2.57 g/g) than native starch. Highest solubility was observed for starch modified by enzymatic method
(EM). Gel consistency of modified pearl millet starch (23.3 to 86.7 mm) was significantly lower than native starch
(109 mm). Starch modified by enzymatic method (EM) showed highest light transmittance whereas light
transmittance exhibited by starch modified by 0.5% epichlorohydrin method (CM3) was lowest. Syneresis of
starch modified by all the methods except pregelatinized starch (PM) and 0.1% phosphorus oxy trichloride method
(CM4) was significantly higher than native starch. As compared to native starch, peak viscosity, final viscosity,
peak time and pasting temperature of starch modified by chemical methods was higher whereas setback and
breakdown was lower. On the other hand, starch modified by 0.5% epichlorohydrin method (CM3) and enzymatic
method (EM) exhibited lower peak and final viscosity than native starch. Addition of pearl millet starch upto 15%
resulted in increase in expansion ratio and sensory score and decrease in bulk density and hardness. Further
increase in level of starch in the formulation decreased expansion ratio and sensory score. Acceptable RTE pearl
millet snacks can be prepared by incorporating 15% pearl millet starch in formulation of pearl millet flour with
17.8% moisture content extruded at 25 kg/hr feed rate and 121 0C temperature with 8 rpm cutter speed. Pearl millet
can be processed for flour and starch, utilized in the formulation for development of RTE extruded snacks with
improved physical and sensory attributes. Thus, processing of pearl millet into starch can be used as an alternative
source of corn starch and can be used for preparation of pearl millet based RTE snacks.
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