Mary Ann Stringer

Evaluating the potential for enzymatic acrylamide mitigation in a range of food products using an asparaginase from Aspergillus oryzae.

Asparaginase, an enzyme that hydrolyzes asparagine to aspartic acid, presents a potentially very effective means for reducing acrylamide formation in foods via removal of the precursor, asparagine, from the primary ingredients. An extracellular asparaginase amenable to industrial production was cloned and expressed in Aspergillus oryzae . This asparaginase was tested in a range of food products, including semisweet biscuits, ginger biscuits, crisp bread, French fries, and sliced potato chips. In dough-based applications, addition of asparaginase resulted in reduction of acrylamide content in the final products of 34-92%. Enzyme dose, dough resting time, and water content were identified as critical parameters. Treating French fries and sliced potato chips was more challenging as the solid nature of these whole-cut products limits enzyme-substrate contact. However, by treating potato pieces with asparaginase after blanching, the acrylamide levels in French fries could be lowered by 60-85% and that in potato chips by up to 60%.

Trichoderma reesei XYN VI – a novel appendage‐dependent eukaryotic glucuronoxylan hydrolase

Expression of a Trichoderma reesei gene coding for a putative GH30 xylanase in Aspergillus oryzae led to isolation and purification of a novel xylanase exhibiting catalytic properties different from those of the previously characterized GH30 xylanase XYN IV of T. reesei. The novel enzyme, named XYN VI, exhibited catalytic properties similar to appendage‐dependent GH30 glucuronoxylanases previously recognized only in bacteria. XYN VI showed high specific activity only on xylans or xylooligosaccharides containing 4‐O‐methyl‐d‐glucuronic acid or d‐glucuronic acid side substituents. The cleavage of the main chain takes place primarily at the second glycosidic linkage from the branch towards the reducing end of the polysaccharides or aldouronic acids. These catalytic properties resemble bacterial GH30 glucuronoxylanases, although the recognition of the uronic acid side chains by XYN VI is apparently based on interaction of the substrate with other amino acids. Moreover, in contrast to bacterial enzymes, XYN VI is also capable of slower but significant cleavage of unsubstituted parts of xylan and acidic xylooligosaccharides. The data point to a great catalytic diversity of xylanases produced by the most extensively studied cellulolytic fungus.