pH-, temperature- and time-dependent activities of endogenous endo-beta-D-xylanase, beta-D-xylosidase and alpha-L-arabinofuranosidase in extracts from ungerminated rye (Secale cereale L.) grain

Activities of endogenous beta -D-xylosidase (EC.3.2.1.37). alpha -L-arabino furanosidase (EC. 3.2.1.55) and endo-beta -D-xylanase (EC.3.2.1.8) were qua ntified in extracts from ungerminated rye (Secale cereale L., var. Amando) grain. pH- and temperature optimum and stability of the unpurified enzymes were examined. The activity of beta -xylosidase and alpha -arabinofuranosid ase against p-nitrophenyl-glycosides was 180 and 346 pkatal/g grain, respec tively (pH 4.5: 30 degreesC) and that of the endo-xylanase against RBB-xyla n was 11 pkatal/g grain (pH 4.5: 40 degreesC). The pH optimum of each for t he enzymes was 4.5, which is similar to the pH of a rye dough. The temperat ure optima for the enzymes were 40 degreesC (endo-xylanase), 70 degreesC (b eta -xylosidase) and 60 degreesC (alpha -arabinofuranosidase), respectively . Sodium chloride (0.5 3.0%, w/v) had no effect on the enzyme activities. T he enzymes were relatively stable at pH 4.5 and room temperature for at lea st 24 h. The enzymes showed no significant decrease in activity when extrac ts were incubated at pH 4.5 and 30 40 degreesC for 80 120 min. Incubation a t temperatures higher that 40 degreesC resulted in a significant decrease i n activity. The rate of hydrolysis of the respective p-nitrophenyl glycosid es and RBB-xylan was under conditions typical for the rye dough production stages but decreased at temperatures typically encountered in the baking pr ocess. (C) 2001 Academic Press.