β‐amylase activity in commercial gluten

Abstract

AbstractThe nature of β‐amylase activity in commercial wheat gluten was examined. Forty‐nine samples of vital wheat gluten from five countries were tested and found to contain large amounts of both ‘free’ (water soluble) and ‘bound’ (extracted with reducing agents, papain or concentrated saline) β‐amylase, although the distinction between these two categories proved somewhat arbitrary. β‐Amylase was not active at extremes of pH (<3 or > 9) but activity was restored on reutralisation. Potassium cyanide reversibly inhibited both ‘free’ and ‘bound’ enzyme. 2′,3′‐Epoxypropyl α‐D‐glucopyranoside irreversibly inhibited the enzyme, but competing solvolysis made this method impractical for large‐scale work. Significant variation was found between the levels of β‐amylase activity in commercial gluten samples (the means of β‐amylase activity for individual countries ranged from 1‐88 to 3‐12 U mg−1 gluten) but this variation was not correlated with bread‐baking quality. β‐Amylase activity of gluten declined with storage, especially after 2 years, but bread‐baking quality was not affected. The decline in β‐amylase activity of experimentally heat‐treated gluten was related to the decline of bread‐baking quality. Exceptionally low β‐amylase activity could be used as a ‘marker’ for gluten that has been heat damaged during the drying process.