HYDROTHERMAL TREATMENT OF STARCH IN PRESE NCE OF ALPHA-AMYLASE .3. CHANGES OF RHEOLOGICAL PROPERTIES OF WHEAT-STARCH BY HYDROTHERMAL ENZYMATIC TREATMENT
G. Stoof et al., HYDROTHERMAL TREATMENT OF STARCH IN PRESE NCE OF ALPHA-AMYLASE .3. CHANGES OF RHEOLOGICAL PROPERTIES OF WHEAT-STARCH BY HYDROTHERMAL ENZYMATIC TREATMENT, Starke, 49(6), 1997, pp. 225-231
In order to change functional properties of wheat starch the feasibili
ty for a hydrothermal enzymatic modification under conditions of exces
s water (annealing) has been tested. The granular structure of the sta
rch should remain unchanged at the same time. Since wheat starch may b
e changed negligiblely at usual conditions of annealing (T=50 degrees
C) as a consequence of its rather low swelling temperature a bacterial
alpha-amylase has been used for partial degradation of these portions
of starch granules which gelatinize irreversiblely at higher levels o
f annealing temperatures. The resulting spectrum of saccharides consis
ting mainly of maltose (approx. 50%) allows the protection of the whea
t starch matrix even at higher annealing temperatures (54 degrees C).
However, the gelatinization and gelation behaviour is changed in a cha
racteristic way, in particular by a serious increase of the hot paste
consistency at 95 degrees C. In the following, the obtained consistenc
y collapses significantly and arrives by cooling a level below the cor
responding figures of the native starch. With respect to yield of anne
aled starch the reaction time at elevated temperature is of main impor
tance. In order to demonstrate the protecting activity of the produced
saccharides in particular with higher concentrations of maltose sampl
es have been annealed in maltose sirups of varied concentration (6, 12
, 25%m/m). Up to concentrations of 12%m/m and reaction temperatures of
50 degrees C the Brabender consistency curves could be raised by 300
to 500BU. The application of 54 degrees C limited the effect of modifi
cation. Using a 25%m/m maltose syrup allowed, of course, successfully
the annealing at 54 degrees C. As expected, yield losses remained low
(<10%). In applying a temperature-time-regime by steps together with a
treatment by alpha-Amylase or alternatively 25%m/m maltose syrup the
expected shifting of consistency curves could be observed as well, how
ever, to a limited amount. Finally, pronounced differences could be fo
und for the yield of modified starches.