Different action patterns of glucoamylases on branched gluco-oligosaccharides from amylopectin

• Branched gluco-oligosaccharides are ideal substrates for glucoamylase screening.
• Glucoamylases had different activities towards branched gluco-oligosaccharides.
• Panose and pullulan in combination can represent branched gluco-oligosaccharides.

A bottleneck in enzymatic starch hydrolysis, like in biofuel industry, is relatively slow degradation of branched structures compared to linear ones. This research aimed to evaluate glucoamylases for their activity towards branched gluco-oligosaccharides. The activity of seven modified glucoamylases and two homologs was compared to that of a reference glucoamylase obtained from a commercial enzyme cocktail ‘Distillase® SSF’. All enzymes were evaluated for their activity towards panose (glc(α1-6)glc(α1-4)glc), pullulan and a purified branched gluco-oligosaccharide with a degree of polymerisation of 5 (bDP5) identified as glc(α1-4)[glc(α1-4)glc(α1-6)]glc(α1-4)glc. The enzymes degraded bDP5 differently, which was mainly due to variation in their capability to cleave α-(1→6)-linked or the α-(1→4)-linked glucosyl residue at the non-reducing end of the branched glucosyl residue. By comparing the enzyme activity towards bDP5 with those towards panose and pullulan, it was suggested that the activity towards bDP5 could be estimated only when the activity towards both commercial substrates was evaluated.