Starch is gelatinised when it is heated in a sufficient amount of
water. During gelatinisation a range of irreversible events occur. The
molecular and crystalline order within the starch granule is lost. The
absorbtion of water leads to swelling and eventual fragmentation of
the granules. Depending on the starch and the conditions used,
leaching of some amylose and amylopectin might be detected (Eliasson
and Gudmundsson, 1996). Starch gelatinisation is an endothermic
process, that can be studied by Differential Scanning Calorimetry
(DSC).
Gelatinisation of starch occurs also when it is subjected to high
pressure at room temperature. The extent of structural changes taking
place during pressurisation depends mainly on the starch type,
concentration and the processing conditions used. DSC has been used by
several researchers to determine the degree of gelatinisation of
starch samples after pressure treatment (Douzals et al., 1996 and
1998; Ezaki and Hayashi, 1992; Muhr and Blanshard, 1982; Stute et al.
1996). Most studies have, however, not taken into consideration the
effect of pressure processing time. In this study the effects of
pressure and processing time on the gelatinisation of three different
kinds of starch in water systems were investigated using DSC.
In order to prevent the sedimentation of starch granules during
pressure processing a carrier system was used. For barley and waxy
maize starch, the carrier system was a 2% heat gelatinised waxy maize
starch paste, whereas for potato starch a 0.4% konjac glucomannan
dispersion was used as carrier system. Native starch was mixed into
the carrier system to a final concentration of 25% (w/w). Starch
samples were treated at different pressures (400-900 MPa) for
different periods of time (0-75 min). The temperature was set at 30
C, but it increased to about 37 C during pressure build-up. Directly
after decompression, the DSC analysis was conducted using a heating
rate of 10 C/min from 10 to 100 C. The transition enthalpy of the
pressure treated starch samples decreased with increasing pressure and
treatment time. For potato starch, the gelatinisation peak disappeared
after a 5 min treatment at 900 MPa. Barley and waxy maize starches
were less pressure resistant. A 10 min treatment at 550 MPa for barley
starch and a 30 min treatment at 600 MPa for waxy maize starch was
enough for an almost complete gelatinisation as determined by DSC.
References
Douzals, J.P., Marechal, P.A., Coquille, J.C. and Gervais, P.,
Microscopic study of starch gelatinization under high hydrostatic
pressure, Journal of Agricultural and Food Chemistry 44 (1996)
1403-1408.
Douzals, J.P., Perrier Cornet, J.M., Gervais, P. and Coquille, J.C.,
High-pressure gelatinization of wheat starch and properties of
pressure-induced gels, Journal of Agricultural and Food Chemistry 46
(1998) 4824-4829.
Eliasson, A.-C. and Gudmundsson, M., Starch: Physicochemical and
functional aspects. In Carbohydrates in Food, ed. A.-C. Eliasson,
Marcel Dekker, New York 1996, pp. 431-503.
Ezaki, S. and Hayashi, R., High pressure effects on starch: structural
change and retrogradation. In High Pressure and Biotechnology, ed. C.
Balny, R. Hayashi, K. Heremans and P. Masson, Colloque INSERM/John
Libbey Eurotext, Montrouge, France 1992, Vol. 224, pp. 163-165.
Muhr, A.H. and Blanshard, J.M.V., Effect of hydrostatic pressure on
starch gelatinisation, Carbohydrate Polymers 2 (1982) 61-74.
Stute, R., Klingler, R.W., Boguslawski, S., Eshtiaghi, M.N. and Knorr,
D., Effects on high pressures treatment on starches, Starch/Stärke 48
(1996) 399-408.
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