HYDROTHERMAL TREATMENT OF STARCH IN PRESE NCE OF ALPHA-AMYLASE .3. CHANGES OF RHEOLOGICAL PROPERTIES OF WHEAT-STARCH BY HYDROTHERMAL ENZYMATIC TREATMENT

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.