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Specific and highly sensitive oligosaccharide-based chromogenic and fluorogenic substrates have been developed for the measurement of trace levels of polysaccharide <i>endo</i>-hydrolases in cereal grains and products. These substrates are used in the presence of saturating levels of specific glycosidases such as thermostable a- and b-glucosidases and b-xylosidase. For the measurement of pullulanase and limit-dextrinase, the substrate is either 4,6-<i>O</i>-benzylidene-2-chloro-4-nitrophenyl-b-maltotriosyl (1-6) a-maltotriose (BzCNPG3G3) as a chromogenic substrate, or 4,6-<i>O</i>-benzylidene-methylumbelliferyl-b-maltotriosyl (1-6) a-maltotriose (BzMUG3G3) as a fluorogenic substrate. a-Amylase is assayed with 4,6-<i>O</i>-benzylidene-4-nitrophenyl-a-maltoheptaose (BzNPG7) and 4,6-<i>O</i>-ethylidene-4-nitrophenyl-a-maltoheptaose (EtNPG7). For assay of <i>endo</i>-cellulase, the substrate 4,6-<i>O</i>-(3-ketobutylidene-4-nitrophenyl-a-cellopentaose (CellG5); for assay of lichenase and 1,3:1,4-b-glucanase (malt b-glucanase) the substrate prepared was 4,6-<i>O</i>-benzylidene-2-chloro-4-nitrophenyl-b-cellotriosyl (1,3)-D-glucose (BzClNPG443); and for <i>endo</i>-xylanase the substrate is 4,6-<i>O</i>-(3-ketobutylidene-4-nitrophenyl-b-xylohexaose (XylX6). On hydrolysis of each of these substrates by the particular <i>endo</i>-hydrolase, 4-nitrophenyl or 2-chloro-4-nitrophenyl oligosaccharide is released and this is immediately hydrolysed by the relevant glycosidase in the reagent mixture, to release 4-nitrophenol or 2-chloro-4-nitrophenyl that produce a yellow color in the presence of an alkaline solution. Assay procedures using these modified oligosaccharides are simple to use, specific, accurate, robust and readily adapted to automation. These methods should find widespread application in the analysis of cereal products and in screening of microbial preparations for the relevant enzyme.