Recent Processing Methods for Preparing Starch-based Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 51

Jackson and co-workers (1988) used mild sonication conditions (20 s at 55 °C) to disrupt
swollen starch granules. This treatment increased the solubility of starch in water without
extensive depolymerization and allowed starch samples to be characterized by HPLC-SEC
without the use of DMSO or alkaline aqueous solvent systems. Sonication for longer than
80 s substantially altered the HPLC-SEC profile.
A patent was issued (Nitsch 1995) on the use of ultrasound to produce high yields of
starch degradation products with narrow molecular weight distributions. Molecular weights
of the sonicated starches could be adjusted by varying the duration and intensity of the
sonication treatment, and contamination with undesired low molecular weight components
could be largely avoided. Proposed applications for these sonicated starch products included
their use as blood plasma substitutes and as components in the preparation of pharmaceutical
products. Schittenhelm and Kulicke (2000) studied the ultrasonic degradation of hydroxyethyl
starch, starch acetate and carboxymethyl amylose in aqueous solution. Since the high-shear
cavitation resulting from ultrasonic treatment causes bond cleavage at the center of gravity in
polymeric materials, this treatment process was an effective method for preparing degraded
polymers of varying molecular weight for use in establishing structure-property relationships.
Comparison of cellulose and starch derivatives showed that the coiled structure of
hydroxyethyl starch was degraded more slowly and yielded a higher limiting molar mass than
the linear derivatives of cellulose.
Chung and co-workers (2002) prepared starch pastes by heating 5% aqueous slurries of
mung bean, potato and rice starches for five minutes at 95 °C; and the hot starch pastes were
then sonicated for 0.25-5min. Treatment with ultrasound reduced the viscosities of the
starch dispersions, reduced the amount of insoluble starch remaining after centrifugation,
and increased the clarity of the starch dispersions. Lipatova and co-workers (2002) prepared
aqueous corn starch pastes at 90 °C and the resulting starch pastes (1-8% starch concentration)
were then treated with ultrasound at a frequency of 22 kHz for 5-60 s. Degradation of the
starch pastes was accompanied by a decrease in viscosity, an increase in transparency, and
an increase in the amount of water-soluble material. For comparison, a portion of the starch
paste was treated with ultrasound and another portion was thermally treated at 105 °C. With
thermal treatment, an 80% disruption of starch granules in a 5% starch paste was observed
after 2 h, whereas with ultrasonic treatment the same amount of disruption was observed in
only 40 s. Compared to thermal treatment, lower viscosities and lower optical densities were
observed with ultrasonic treatment at 40 °C. The sharp decrease in viscosity was attributed
to disintegration of swollen starch granules in the first few seconds of ultrasonic treatment.
Czechowska-Biskup and co-workers (2005) studied the effects of 360 kHz ultrasound on
aqueous solutions of chitosan and corn starch, and observed that ultrasonic treatment
reduced the molecular weights of both polysaccharides. Comparison of results obtained in
the presence and absence of tert -butanol (a scavenger for hydroxyl radicals) suggested that
degradation was caused by both mechanochemical effects and reactions of the polysaccharides
with hydroxyl radicals generated during the cavitation process. Chain scission depended
upon polymer concentration, ultrasonic power, and the gas used to saturate the aqueous
solution. Ultrasound-induced chain scission of starch proceeded with lower yield than that
observed with chitosan, probably due to the different chain conformation of starch, compared
to the rod-like conformation of chitosan. Ida and co-workers (2008) studied the sonication
of starch pastes prepared by heating 5% and 10% aqueous dispersions of waxy maize,
potato, tapioca and sweet potato starches at 90 °C for 60 min. When 10% pastes prepared
from waxy maize starch were sonicated at 80, 60 and 40 °C, the lowest final viscosities were
observed at the lowest sonication temperatures, indicating that cavitation was more effective