Biomedical Engineering Reference
In-Depth Information
samples gave similar results. With glucoamylase, ultrasound enhanced the reaction rate at
starch concentrations up to 50 g per liter. Increases in reaction rate were attributed to an
increase in the efficiency of mixing and diffusion of reaction components in the sonicated
mixtures. Khanal and co-workers (2007) used ultrasound to treat slurries of corn to enhance
the formation of glucose from corn starch by enzymatic hydrolysis with
-amylase and
glucoamylase. Treatment with ultrasound decreased the size of corn particles and thus
increased the formation of glucose, although prolonged use of high power settings reduced
glucose formation due to denaturing of enzymes. This technology could find use in processes
used for ethanol production.
Shewale and Pandit (2009) explored the use of ultrasound to enhance the hydrolysis of
starch to glucose in sorghum flour using
α
-amylase and amyloglucosidase. Treatment at a
frequency of 20 kHz for one minute decreased particle size and increased saccharification;
the results were largely attributed to the increased availability of starch for hydrolysis due to
ultrasound-assisted disruption of the protein matrix surrounding starch granules. Chan and
co-workers (2010) examined the effect of sonication on the removal of proteins from the
surfaces of corn starch and mung bean starch granules using 2% aqueous solutions of
sodium dodecyl sulfate (SDS). Although the amount of surface protein was reduced by SDS
treatment, no significant difference was observed between the results obtained with and
without ultrasound. The X-ray diffraction patterns of SDS-treated starch samples were
identical to those of the native starches, indicating that helical inclusion complexes with
SDS were not formed during the treatment. Nikoli
α
and co-workers (2010) investigated the
possibility of improving glucose yields and ethanol productivity by using an ultrasound
pretreatment in the production of bioethanol by saccharification and fermentation of corn
meal in a batch system. Pretreatment of 1:3 corn meal:water mixtures at 40 kHz under the
optimum conditions of five minutes at 60 °C increased the concentration of glucose and
improved ethanol production.
Treatment with ultrasound was also investigated as a method for isolating starch granules
from cereal grains without the use of some of the chemicals commonly used conventional
wet-milling processes. The use of ultrasound in the isolation of rice starch was investigated
by Wang and Wang (2004a). The surfaces of isolated starch granules were not damaged by
sonication and, by combining a surfactant (particularly SDS) with the ultrasonic treatment,
the yield of starch was increased and the amount of residual protein was decreased. The
same authors investigated the effect of ultrasonic treatment on the efficiency of starch
isolation when ultrasound was employed before, during, and after treatment with protease
enzyme (Wang and Wang, 2004b). Starch isolation was improved by combining neutral
protease with ultrasound, the preferred method of treatment was digestion with protease for
2 h followed by sonication for 15 or 30 min. Size exclusion chromatography and SEM
showed no depolymerization of starch and no damage to starch granule surfaces. Zhang and
co-workers (2005b) examined laboratory-scale wet-milling procedures using ultrasonic
treatments at different points in the milling of corn starch; the results were compared with
corn that was processed by conventional wet milling in the presence of sulfur dioxide.
Starch yields obtained with ultrasound were comparable to those obtained by conventional
wet milling and the starches isolated using ultrasonic treatment exhibited somewhat higher
paste viscosities. Zhang and co-workers (2005a) also examined the use of ultrasound to
enhance the yield of starch obtained from degermed corn flour and from hominy feed.
Higher starch yields were obtained from the ultrasound-treated samples; grinding alone did
not significantly enhance the yield of starch. Cameron and Wang (2006) observed that the
combined action of neutral protease and sonication was effective in isolating starch from
ć
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