Recent Processing Methods for Preparing Starch-based Bioproducts - Food and Industrial Bioproducts and Bioprocessing - page 71

and pasting properties of starch granules; these techniques could be used to increase the
percentage of slowly-digestible, resistant starch in food products. The application of high
pressure has been shown to reduce the gelatinization temperature of starch; this processing
method will enable starches in food products to be processed without the detrimental effects
of high temperature on heat-sensitive food components. Also, protein-based sources of
food spoilage, such as enzymes and microorganisms, can be denatured and inactivated by
high-pressure processing.
Microwave heating for starch processing has been extensively investigated and is more
rapid and uniform than conventional thermal heating. Reactions of starch have been shown
to take place with shorter reaction times when microwave heating is used. Investigations of
ultrasound in starch processing have shown that the high-shear cavitation resulting from
ultrasonic treatment reduces the molecular weight of starch, and yields starch solutions with
less insoluble material, lower viscosity, and increased clarity. Bond cleavage occurs at the
center of gravity and produces degraded starch products with narrow molecular weight
distributions and minimal contamination with low molecular weight material. Shorter
reaction times have also been observed when ultrasound was used during the preparation of
starch derivatives. Treatment with ultrasound has been shown to enhance glucose production
from flour and corn meal, and this technology could lead to increased ethanol production
during saccharification and fermentation. Incorporating ultrasound into the wet-milling
process facilitated the isolation of starch granules from cereal grains.
Extraction with supercritical CO 2 was shown to be a viable process for removing
undesirable contaminants from starch and for extracting lipids from wheat flour. This
method of extraction eliminates the hazards and environment concerns associated with
traditional extraction methods using organic solvents. A method was also developed for
preparing expanded foams or puffed products from starch by adding supercritical CO 2
during extrusion. Supercritical CO 2 thus replaces steam as the blowing agent, resulting in
foams with improved properties. Supercritical CO 2 has also been used as a reaction medium
for preparing starch derivatives and starch-based matrices with potential applications as
scaffolds for tissue engineering. A biomass conversion system using supercritical water has
also been developed to convert starch and other biomass into gaseous products.
Extrusion is a rapid and continuous method for preparing new starch products and
derivatives. There is interest in these materials because of the low cost of starch, the
desirability of replacing petroleum-based materials with renewable feedstocks, the improved
biodegradability of starch-based materials, and the creation of new markets for agricultural
commodities. Steam jet cooking has been used to prepare stable starch-oil composites
useful in food products and as water-based lubricants. Spherulites that could have practical
end-use applications have also been prepared.
Future years should see an increase in the use of these new processing techniques and
other non-traditional methods of processing will also be developed. The current interest in
biodegradability and the replacement of petrochemical-based materials with agricultural
products will result in increased research on starch as a starting material for new products.
REFERENCES
Akdogan H. 1999 . High moisture food extrusion . Int J Food Sci Technol 34 : 195 - 207 .
Alavi SH , Gogoi BK , Khan M , Bowman BJ , Rizvi SSH . 1999 . Structural properties of protein-stabilized
starch-based supercritical fluid extrudates . Food Res Internat 32 : 107 - 118 .