Abstract
Two sprout-damaged wheat lots with the falling number values of 91 and 65 were heat-treated by immersing the grain in water of temperatures of 80, 85, 90 and 100°C, followed by rapid chilling in water. The purpose of the treatment was to suppress the excess a-amylase activity in the outer layers of the kernels. The a-amylase activity following the treatment was measured by the falling number test. The increase in the falling number value was the greater the longer the treatment lasted and the higher the water temperature was. Processing lasting 30 sec at 80, 85, 90 and 100°C increased the falling number value of the one lot from 91 to 105, 117, 133 and 238 and of the other lot from 65 to 69, 70, 98, 163, respectively. As the falling numbers increased the wet gluten content of the samples decreased. These changes had a negative correlation. The gluten quality showed heat damage when the amount of gluten had dropped by about 5 and 2 precentage units in the lots with the falling numbers 91 and 65, respectively. This occurred at processing of the lot of better quality for 70, 20, 13 and 6 sec in the order of increasing temperature. The corresponding durations for the other lot were above 60, 30, 20 and 6 sec. During these treatments the falling number values rose from 91 to 104—129 and from 65 to 70—71. These results were confirmed by farinogram and extensigram determinations and by baking tests. The same processing conditions affected more severely the lot having the better initial quality than the lot with greater sprout damages.
Highlights
During sprouting the activity of a-amylase in the grain increases exponentially as a function of time (Olered 1963, Dronzek et al 1972)
Under conditions closely resembling those prevailing in wheat bread during baking, about 90 % of the activities of /?- and aamylases were destroyed at about 75 and 85° C, respectively (Walden 1955)
Jongh (1967) showed that the amylases lost their activity at baking when the temperature had risen to about 78° C
Summary
During sprouting the activity of a-amylase in the grain increases exponentially as a function of time (Olered 1963, Dronzek et al 1972). A high a-amylase activity impairs the baking quality of the flour in that the gelatinized starch is rapidly degraded to water soluble sugars at baking. The gelatinized starch is susceptible to amylase attack until the enzyme is inactivated by heat (Bean et al 1974). This degradation lowers the water imbibing properties of starch and the crumb of the breads become damp and doughy (Thomas and Luckow 1969). The amylase activity of grain or flour can be depressed or inactivated by heat or by chemical agents. Under conditions closely resembling those prevailing in wheat bread during baking, about 90 % of the activities of /?- and aamylases were destroyed at about 75 and 85° C, respectively (Walden 1955). Jongh (1967) showed that the amylases lost their activity at baking when the temperature had risen to about 78° C
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