2001 AACC Annual Meeting Charlotte, North Carolina October 14-18, 2001 Charlotte Convention Center

Staling of bread is defined as an increase in crumb firmness and corresponding loss of product freshness. Bread staling is caused by a gradual transition of starch from an amorphous structure to a partially crystalline state due to a retrogradation phenomenon in which starch molecules associate through inter- or intramolecular hydrogen bonding. Novamyl [1] (glucan 1,4-a-maltohydrolase) is added as an antistaling agent that through its characteristic substrate specificity acts on and partially degrades the starch and thereby reduces retrogradation. Novamyl is a medium thermostable amylase showing distinctly different substrate specificity from that of typical exo-amylases by the ability of Novamyl to hydrolyse maltooligosaccharides modified at the non-reducing end [2]. To explore the possibilities of improving the functionality of Novamyl, e.g. by changing the substrate specificity or increasing the thermostability, the Novamyl encoding gene was subjected to mutagenesis followed by screening. Using directed evolution a substantial number of variants with changed functionality were obtained. Novamyl variants with markedly enhanced thermostability, above 10 C in Tm-values, were thus obtained. The thermostabilised variants furthermore displayed changed product specificity showing a clear tendency towards producing longer maltooligosaccharides. The variants of Novamyl showed enhanced industrial performance most likely due to the increased thermostability and changed substrate specificity. [1] Outtrup, H., & Norman, B.E. (1984) Starch/Stäerke 36, 405-411 [2] Christophersen, C., Otzen, D.E., Norman, B.E., Christensen, S., & Schäfer, T. (1998) Starch/Stäerke 50, 39-45