Gelatinisation Characteristics and Enzyme Susceptibility of Different Types of Barley Starch in the Temperature Range 48-72°C1

Abstract

The gelatinisation temperatures, pasting characteristics and enzymic susceptibilities in the temperature range 48-72°C of normal, high amylose, low amylose and zero amylose barley starches were determined. Normal starches had the lowest gelatinisation temperatures, but low and zero amylose starches had the lowest pasting temperatures. Normal starches were the most readily soluble in water at 48-60°C in the presence of a mixture of α-amylase, β-amylase and limit dextrinase and were most readily broken down to reducing sugars by these enzymes. High amylose starch was the most resistant to enzymic hydrolysis in the temperature range 48-72°C and, hence, produced the lowest level of reducing sugars.Key words: Barley, enzymic hydrolysis, gelatinisation, high amylose, pasting, starch, waxy.-2863(9'8-32The rapid and efficient conversion of starch to fermentable carbohydrates during brewing is dependent on a number of parameters including the level of starch degrading enzymes in the malt, the gelatinisation temperature of the starch and the actual temperature program of the mash. Starch hydrolysis is carried out by a number of malt enzymes working together. These include α-amylase, β-amylase, limit dextrinase and α-glucosidase 20,21 . Although α-amylase is able to hydrolyse intact starch granules, the rate of hydrolysis is very slow compared to that of solubilised starch 27,29 . Effective hydrolysis by α-amylase, therefore, occurs only after the starch has been solubilised (or gelatinised). When this has occurred, the enzyme rapidly degrades the starch components through random hydrolysis with concomitant reduction in the viscosity of the starch solution and formation of degradation products 22 that are substrates for β-amylase action. It is this action of β-amylase that is largely responsible for the conversion of starch to the major fermentable carbohydrates, glucose, maltose and maltriose 25 . β-Amylase, however, is relatively heat labile and rapidly loses activity 28 when mashing temperatures rise over 62.5°C. It is essential, therefore, that malt starch is gelatinised at or below this temperature to permit β-amylase to complete its action before losing a significant amount of activity through heat inactivation.The preferred substrates for limit dextrinase are the branched dextrins formed from starch by the combined action of α-and β-amylases 21 . Limit dextrinase appears to have only limited action during mashing, however 10 . This is caused, probably, through inhibition by low molecular weight inhibitors in the malt 17 rather than by excessive lability at mashing temperatures 28 . α-Glucosidase may play a role during mashing by hydrolysing small maltodexrins to glucose but the importance of α-glucosidase action remains unclear 31 .Several methods have been used to measure the gelatinisation (solubilisation) temperatures of starch granules but each tends to measure a different aspect of this complex phenomenon 2,34 and so not all methods give the same result. One of the most common methods, differential scanning cal...

Optimization of Malting Conditions for Two Black Rice Varieties, Black Non-Waxy Rice and Black Waxy Rice (Oryza sativa L. Indica)

“…The results of gelatinization temperature of the two rice varieties are shown in Table I and these results agree with other reports, that non-waxy starch has a lower gelatinization temperature than waxy starch 19 . The gelatinization temperature of the malted rice was in the range of 64-66.8°C, which was lower than the unmalted form; 71°C and 73°C for black non-waxy rice and black waxy rice, respectively.…”

Effects of Wheat Starch Contents on Malt Qualities

“…Studies on barley found that the malt qualities 3,5 , especially the extract yield 8 , depend on the endosperm components of starch and the protein and structure. During the germination and mashing process, a range of fermentable sugars, which are the main components that constitute the extract of the wort, are produced from the hydrolysis of starch 9 . Starch is composed of amylose and amylopectin.…”

Catalytic Activity of β‐Amylase from Barley in Different Pressure/Temperature Domains

“…Hence, solubilization or gelatinization is a prerequisite of starch hydrolysis. MacGregor et al (27) found that the pasting temperatures of the starches raised with the content of amylose. However, starches with an amylose content of ca.…”