Hydrothermal treatment of starch in presence of alpha-amylase. Part 4: Changes of properties of potato starch by hydrothermal enzymatic treatment

English. Aim of this investigation was to alter functional properties without changing the granular structure of potato starch by hydrothermal enzymatic modification under conditions of excess of water (annealing). Potato starch can be modified hydrothermally without addition of alpha-amylase 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 enzymatically by bacterial alpha-amylase. But, the resulting spectrum of carbohydrates 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 damage of potato starch granula. This agrees with results of electron microscopical investigations on starch granula. Which show large cavities after the modification procedure. Furthermore, high temperatures alter reactions of gelatinization and gelation behaviour in a characteristic manner, for instance by a strong decrease of the hot past consistency at 96 degrees C. Hydrothermal enzymatic modification of potato starch 24 hours long at temperatures up to 70 degrees C causes a dramatic decrease of the Brabender consistency in comparison to untreated starch. The consistency at the beginning of the keeping phase at 96 degrees 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 fully. The difference in the DSC swelling temperature amounts to apparently 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 alpha-amylase are not simply transferable to a hydrothermal enzymatic treatment of potato starch. To change functional proper ties of starches of different botanical origin distinctly one has to adopt the conditions of annealing to the specific structure of the corresponding starch. A hydrothermal enzymatic modification of potato starch is inappropriatefor achieving starch preparations with an increased set back.

German. Mit dem Ziel, funktionelle Eigenschaften von Kartoffelstaerken unter weitestgehendem Erhalt der granulaeren Struktur zu veraendern, wurden Moeglichkeiten zur hydrothermisch-enzymatischen Modifizierung bei Wasserueberschuss (Temperung) der Staerke ueberprueft. Kartoffelstaerke kann ohne Zusatz von alpha-Amylase hydrothermisch modifiziert werden. Dazu sind Temperungszeiten von mehreren Tagen erforderlich. Um diesen Prozess zu beschleunigen, wurde bei hoeheren Temperungstemperaturen (50 Grad C) gearbeitet. Der dadurch entstehende irreversibel gequollene Staerkekornanteil wurde durch zugesetzte Bakterien-alpha-Amylase abgebaut. Der hierbei entstehende Maltosesirup, der zu ca. 50% aus Maltose besteht, vermag die granulaere Form der Kartoffelstaerke jedoch nur in grosseren Konzentrationen zu schuetzen. Durch den enzymatischen Abbau waehrend der Temperung wird die native granulaere Form der Kartoffelstaerke stark geschaedigt. Elektronenmikroskopische Untersuchungen belegen das anhand grosserHohlraeume in den Koernern. Das Verkleisterungs- und Gelbildungsverhalten wird durch diese Art der Behandlung in charakteristischer Weise veraendert. Die Ergebnisse belegen, dass die beschriebenen Temperungsbedingungen in Gegenwart von alpha-Amylase nicht einfach auf eine hydrothermisch-enzymatische Behandlung der Kartoffelstaerke uebertragbar sind.