Action on Potato Starch

Limit Dextrins from Different Starches with Taka-amylase 

---

The data19 summarized in Figure 1 show that the extent of the hydrolysis of soluble potato starch by barley beta amylase reaches a limit which is independent of the concentration of the amylase. The data are typical of the action of beta amylases on unfractionated starches, when the hydrolyses are carried out at or near pH 4.5.1 3 6 19 20 Under these conditions, the hydrolysis of unfractionated starches usually ceases when 60 to 64% of the maltose theoretically obtainable from the substrate has been formed. The exact value of the limit obviously will depend upon the concentration of amylopectin in the starch and upon its structure. 

Anionic starches are obtained by reaction with phosphoric acid and alkali metal phosphates or by derivatization with carboxymethyl groups.30,31 This modification is primarily used to introduce amphoteric properties into cationic com starch for application on the wet end of the paper machine. Anionic starches with carboxymethyl substitution are used as thickeners in coating colors or as binders in coatings for specialty paper grades. Oxidized starches are inherently anionic but without thickening action. Potato starch already carries sufficient natural anionic charge to provide amphoteric properties after cationization.32... 

Assuming that potato starch contains 23 % amylose, the amylopectin must yield 49 % maltose by action of the /3-amylase. If the potato starch contains 5% end groups, the amylopectin should contain 6.5%. Taking this value, /3 = 0.065, we find = 0.56 and fs = 0.51. On the other hand, if we assume that potato starch contains branched molecules with an average degree of ramification expressed by /3 = 0.05, then ts = 0.59 and fs = 0.54. 

Most amylases have only a slight action on the phosphate groups. As mentioned before, the 3-dextrin from potato starch contains all the phosphorus of the starch. This is in accordance with the fact that the phosphorus is concentrated in the amylopectin. A /3-dextrin from arrow-root starch had a phosphorus content of 0.051 % while the starch itself had 0.019%. Since the /3-dextrin corresponds to 40% of the starch, it is evident that here also all the phosphorus is left in the /3-dextrin. 

Most amylase preparations have a certain phosphatase activity. Some of the preparations used in our experiments were tested on glycerophosphate (Table XXVI) at pH 5.3 and 30°. Parallel experiments with potato starch (Table XXVI) show that the action of the phosphatases on the combined phosphoric acid in starch or limit dextrins, respectively, is very slight compared to the action on glycerophosphate. It is not clear... 

The CGTase action was evaluated on cassava starch, sweet potato starch, com starch, and waxy com starch. Substrates concentrations were at 2.5%. Enz5mie, conditions, and quantity were conducted as described above, except that aliquot samples were withdrawn periodically until 24 h. In an independent experiment, starches were gelatinized by autoclave process. The percentage of starch converted into CDs was calculated by ratio of total grams of CDs formed divided per gram of starch and multiplied per 100. 

Generally, starches contain about 20 to 30% of amylose and 70 to 80% of amylopectin, and these concentrations change with the botanical source of starch. Cassava starch, sweet potato starch, com starch, and waxy com starch showed, respectively, 17.0, 20.7, 25, and less than 1% of amylose (28,29, 30). The ratio amylose/amylopectin is an important factor to consider for CD production. The helicoidal stracture of amylose with loops of six to seven glucose imits can contribute with action of CGTase on a- and 3-CD formation (2). 

The /3-amylases in the absence of the a-amylases are incapable of degrading whole starches completely. The hydrolysis proceeds rapidly until about 50 to 55 % of the theoretical amount of maltose is produced and then very slowly until a limit of about 61 to 68% is reached (101), The solution is still viscous and the residue, called a /3-amylase limit dextrin, is unfer-mentable. The limit dextrin arises from the inability of /3-amylase to act beyond a branch point in the randomly branched amylopectin molecule and may be envisaged as a pruned amylopectin structure. In the case of potato starch, the /3-limit dextrin includes all the associated phosphate. The limit dextrin contains one end group for every 10 to 12 D-glucose residues (102), in contrast to one in every 25 or 30 residues for the original amylopectin. The initial attack of /3-amylase on amylopectin is about 20 times as fast as on amylose (103), Maltose in amounts of 53 to 62 % of the theoretical have been reported from the action of /3-amylases on amylopec-tins separated from various starches (104). When the /3-limit dextrin is cleaved by acid hydrolysis or by the action of a-amylase, the structure is opened and new chain ends are made available which can be further acted upon by i3-amylase. 

Glucose derivatives. a-D-Glucose i-phosphate can be prepared by the action of potato phosphorylase on starch or synthesized from acetobromo glucose and trisilver phosphate or silver diphenyl phosphate . 

---