G. Stoof et al., HYDROTHERMAL TREATMENT OF STARCH IN PRESE NCE OF ALPHA-AMYLASE - PART4 - CHANGES OF PROPERTIES OF POTATO STARCH BY HYDROTHERMAL ENZYMATIC TREATMENT, Starke, 50(2-3), 1998, pp. 108-114
Aim of this investigation was to alter functional properties without c
hanging the granular structure of potato starch by hydrothermal enzyma
tic modification under conditions of excess of water (annealing). Pota
to starch can be modified hydrothermally without addition of alpha-amy
lase but annealing needs a number of days. In order to accelerate this
procedure, higher temperatures have been used favouring the formation
of an irreversible swollen starch portion which can be degraded enzym
atically by bacterial alpha-amylase. But, the resulting spectrum of ca
rbohydrates comprising apparently 50% of maltose protects the granula
of potato starch only at higher concentrations. Hydrolytic degradation
by bacterial alpha-amylase during annealing causes therefore strong d
amage of potato starch granula. This agrees with results of electron m
icroscopical investigations on starch granula. which show large caviti
es after the modification procedure. Furthermore, high temperatures al
ter reactions of gelatinization and gelation behaviour in a characteri
stic manner, for instance by a strong decrease of the hot past consist
ency at 96 degrees C. Hydrothermal enzymatic modification of potato st
arch 24 hours long at temperatures up to 70 degrees C causes a dramati
c decrease of the Brabender consistency in comparison to untreated sta
rch. The consistency at the beginning of the keeping phase at 96 degre
es C amounts only to 150 BE and increases to 390 BE at the end of the
cooling phase at 50 degrees C. However, the material does not swell fu
lly. The difference in the DSC swelling temperature amounts to apparen
tly 13 K. The gain of modified starch is increased from 35% up to 48%
without changes in properties, if the temperature in the final keeping
phase of the annealing procedure is not higher than 66 degrees C. The
results confirm that the used annealing conditions in presence of alp
ha-amylase are not simply transferable to a hydrothermal enzymatic tre
atment of potato starch. To change functional proper ties of starches
of different botanical origin distinctly one has to adopt the conditio
ns of annealing to the specific structure of the corresponding starch.
A hydrothermal enzymatic modification of potato starch is inappropria
te for achieving starch preparations with an increased set back.