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Effects of Mutant Thermostable α-Amylases on Rheological Properties of Wheat Dough and Bread

¹Lab. of Food Chemistry, Graduate School of Agriculture and Biological Sciences, Osaka Prefecture University, 1-1, Gakuen-cho, Sakai, Osaka 599-8531, Japan. ²Present address: Department of Life and Health Sciences, Hyogo University of Teacher Education, 942-1, Shimokume, Yashiro, Hyogo 673-1494, Japan. ³Division of Research and Development, Daiwa Kasei K. K., 4-19, Hie-cho, Kosei-cho, Koka, Shiga 520-3203, Japan. ⁴Corresponding author. Phone: +81-72-254-9459. Fax: +81-72-254-9921. E-mail: morita@biochem.osakafu-u.ac.jp.

Thermostable mutant α-amylases (21B, M111, and M77) with various degrees of thermostability were purified from Bacillus amyloliquefaciens F and used as improvers for breadmaking. Test baking with the mutant enzymes was conducted using the long fermentation sponge-dough method. Addition of an appropriate amount of mutant α-amylases to the ingredients distinctly increased the specific volume of the bread and improved the softness of breadcrumb as compared with the addition of Novamyl (NM), an exo-type α-amylase. M77 was the most effective in retarding the staleness of breadcrumb. The softness of breadcrumb during storage, however, was not correlated with the thermostability. All mutant α-amylases weakened the mixing property of the dough, whereas they strengthened the property of fermented dough. Especially, M77 and NM had different effects on the dough properties, but their bread qualities were similar to each other. The strong tolerance of M77 dough to the long baking process might be due to the production of hydrolyzed starches, oligosaccharides in the range of maltopentaose to maltohexaose, as compared with NM. Therefore, in the light of present findings, these mutant α-amylases are possible substitutes for NM as bread improvers.