Recent Processing Methods for Preparing Starch-based Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 43

granule shape after pressure treatment, SEM images of pressure-treated waxy corn starch
showed complete breakdown of the granule structure. High-pressure treatment for nine
minutes did not alter the molecular weight distribution of high amylose corn starch. However,
a polydisperse product was obtained when waxy corn starch was pressure-treated in the
same manner.
Since waxy starches are more sensitive to high-pressure treatment than amylose-
containing starches, the properties of waxy rice and waxy corn starches, pressure-treated at
500 MPa, were studied to determine their texturizing properties for potential applications in
food products (Simonin et al . 2009). Whereas normal corn starch granules swelled gradually
with increasing time under pressure and retained their granule structure, the waxy corn
starch granules lost their granular structure during pressure treatment. Waxy rice starch was
the most sensitive to high-pressure treatment; after ten minutes at 500MPa the granular
structure was lost and the gel reached its maximum viscosity.
The retrogradation kinetics and water dynamics of wheat starch, pressure-treated in
water at 25 °C and 621 MPA, were investigated and compared with thermal gelatinization in
a boiling water bath for 30 min (Doona et al ., 2006 ). The pressure-treated and heat-treated
wheat starch granules showed similar degrees of swelling, and partial disintegration was
observed for the heat-treated granules. Similarities between the pressure-treated and
heat-treated starches observed by microscopy were attributed to the higher starch
concentrations (40%) used in this study. DSC was used to determine enthalpy changes in the
starches during storage for 14days at 4°C. The pressure-treated starch showed a lower
increase in enthalpy during storage than the heat-treated starch, suggesting less retrogradation.
NMR analyses of proton relaxation times suggested different water dynamics in the
pressure-treated and heat-treated wheat starches.
The effect of starch concentration on the pressure-induced gelatinization of potato starch
was determined by pressure treating aqueous dispersions containing 10-70% potato starch
at 40 °C and 400-1200 MPa (Kawai et al ., 2007a). DSC was used to determine the extent of
gelatinization and showed that gelatinization increased with increased pressure and water
content. Retrogradation was observed in mixtures with starch solids of 30-60%, and was
observed at lower treatment pressures when the water content was increased. DSC was also
used to determine whether longer treatment times would affect the gelatinization and
retrogradation of potato starch (Kawai et al ., 2007b). Treatment pressures used in this study
were 600, 800, and 1000MPa, starch concentrations were 10-70%, the treatment
temperature was 40 °C, and the treatment times were 18 and 66 h. Although gelatinization
and retrogradation were significantly affected by the treatment pressure and water content,
increasing the pressure-treatment time from 1 to 66h had little effect on the observed
enthalpy changes.
Błaszczak co-workers (2007) examined the high-pressure treatment of high amylose
starch and waxy maize starch, as well as their 1:1, 1:3, and 3:1 mixtures. Starches were
dispersed in water to give 30% starch solids, and the dispersions were pressure-treated at
20 °C for nine minutes at 650 MPa. Treatment of high amylose starch resulted in only 10.8%
gelatinization, whereas 85.9% gelatinization was observed for waxy maize starch. Granule
disintegration was also observed with waxy maize starch and a gel-like dispersion was
obtained. When mixtures of the two starches were pressure treated, amylopectin formed a
continuous gel phase, while the intact high amylose starch granules acted as fillers in these
mixed systems. In a subsequent study, native and high-pressure treated waxy maize and high
amylose starches were studied by electron paramagnetic resonance spectroscopy (EPR) to
determine the nature, number, and stability of free radicals generated when the starches