Gelatinized Potato Starch Research Articles

Formation of active derivatives of glucoamylase I during the digestion with fungal acid protease and .ALPHA.-mannosidase.

Glucoamylase I (MW 90,000; N-terminal alanine) was selectively produced by a submerged culture of Aspergillus awamori var. kawachi as an enzyme having the ability to digest even raw starches, and was converted into a modified active glucoamylase decreasing in molecular weight during the digestion with the acid protease of the same mold strain. The modified glucoamylase (MW 83,000; N-terminal alanine plus isoleucine) was resembled to an intermediate type of glucoamylase I′, and exhibited hydrolysis curves for gelatinized potato starch and maltose in the same manner as that of glucoamylase I; but it did not digest raw starches and was not adsorbed onto cornstarch, and showed the lower hydrolysis limit of 80 percent for glycogen. The carbohydrate contents of glucoamylase I decreased 59 percent during the digestion with fungal α-mannosidase. The carbohydrate-split glucoamylase (MW 86,000; N-terminal alanine) was unstable at pH 9 or at 65°C in the same extent as glucoamylase I′, but was identical with glucoamy...

The formation and properties of subtilisn-modified glucoamylase.

The glucoamylase I which was purified from a culture of Aspergillus awamori var. kawachi as an enzyme having an ability to digest raw starch, was converted to a modified enzyme with decrease in molecular weight and carbohydrate content by incubation with subtilisin in 0.01 m phosphate buffer, pH 6.8, at 30°C. The modified glucoamylase, isolated by the DEAE-Sephadex A–50 column chromatography, showed a 77% specific activity, and the same manner of the hydrolysis curve for gelatinized potato starch and maltose as the native enzyme, but showed no digestibility for raw starches nor adsorbability onto raw corn-starch, and a lower hydrolysis limit of 80 per cent for glycogen. Stabilities also decreased at pH 9 and at 65°C, respectively. Protease was proved to change the properties of glucoamylase.

Water binding by potato starch

SummaryA tentative rough model for water binding in potato starch based on vapour sorption isotherms and calorimetric data is proposed. Heats of immersion and derived thermodynamic quantities are given. A constant differential net heat of sorption for the first 10% of water on dry starch was found. Sorption isotherms for water vapour of native and gelatinized potato starch showed good agreement with the Guggenheim sorption equation up to water activity 0.93 and with the Brunauer Emmet and Teller sorption equation up to water activity 0.3. The water binding mechanism was absorption, without evidence of capillary condensation, up to water activity of 0.95.

Food Chemical Studies on Starch Part 1. Effect of Urea on the Gelatinization of Potato Starch

The swelling ratio and solubility of potato starch with urea were studied to elucidate the effect of urea on the gelatinization of starch. The swelling ratio and solubility were increased with the increasing of urea concentration and raising the temperature. The concentration of urea required for the initial gelatinization decreased on elavating the temperature as follows; 6 M/l at 20°C, 4.5 M/l at 30°C, 3.2 M/l at 40°C and 1 M/l at 50°C. The initial gelatinization temperature of potato starch at zero concentration of urea was estimated about 56°C, and this agreed with the result obtained by Kofler microscope methods. The swelling ratio above 3.5 M/l urea at 60°C was lower than those at other temperatures (2050°C). A lower swelling ratio is due to the decrease in the amount of precipitates because of a higher solubility at a higher temperature. There was not the increase of swelling ratio between 3.5?`5.5 M/l urea at 50°C and 6.58 M/l at 40°C. These results suggest that the swelling ratio is not primarily connected only to the degree of gelatinization. The urea inhibited the starch-iodine reaction, and inhibition of starch-iodine reaction by urea was remarkable at the low iodine concentration.