279Starch hydrolysis in malting and mashing processes was studied by gel chromatography on Sepharose Cl 4B. The final molecular weight distribution of starch components in malt differs from those in barley. During malting a molecular weight fraction close to the void volume appears as an intermediate product. Minor differences in starch hydrolysis in mashes with different malts is obtained, though the final dextrin composition of the worts is similar.
The initial stages in ct-amylolysis of large and small barley starch granules were followed by gel chromatography. Hydrolysis of gelatinised large and small granules is very similar, indicating a similar structure of the individual components in the two starches. Amylolysis of intact large granules is quite different from that of intact small granules, suggesting differences in the mode of packing of the starch components within the granules. It is concluded that a-amylolysis is of a non-random nature, probably due to the amylopectin component of the starch. On the basis of the intermediate products obtained, a possible structure for the amylopectin molecule is presented, based on a unit cluster with a molecular weight of 3 X 10*.
The distribution of molecular size of the native starch prepared according to a new method and of oxidised products of starch has been investigated with the help of agarose gel filtration. It has been noticed that the curve of the molecular distribution of the native wheat starch (product A) shows a big peak excluded by the gel with M̄W > 2 · 106 comprising about 58% of the sample and a part fractioned by the gel within the area 1 · 104 < M̄W < 2 · 106. Comparative gel filterings of native maize, tapioca and potato starch have shown that the distribution of molecular size of wheat starch (A) most resembles that of maize starch. Tapioca starch and especially potato starch have a somewhat lower percentage of molecules within the part fractioned by the gel than wheat starch (A). Native wheat starch, product B has a somewhat higher percentage of molecules within the area 1 · 105 > M̄W > 2 · 104 than the other native types of starch.
Heat‐treatening and oxidation of native starch causes a decrease or a disappearance of the macromolecular excluded part of the sample and instead increases the molecules within the fractioning area of the gel, M̄W < 2 · 106. The used gel chromatographic method is thus very suitable when investigating the distribution of molecules of oxidised starch products and in product control.
The time course for hydrolysis of starch with α‐amylase and oxidation of starch with Na‐hypochlorite was studied with the aid of gel chromatography. It was found that the initial steps in the hydrolysis can be described as a consecutive reaction in which the fractions Mw > 5 · 105, 5 · 105 > Mw > 1 · 105 and Mw < 1 · 105 are contained. The reaction in the course of decomposition with α‐amylase is one of the first order, while decomposition by means of hypochlorite is a second order reaction. There are considerable differences in the changes in molecular weight distribution between the two methods. Hydrolysis with α‐amylase gives a solution with a symmetrical molecular weight distribution whereas hypochlorite oxidation obviously causes splitting of some of the starch molecules, which results in solutions with two molecular weight maxima.
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