European Young Cereal Scientists and Technologists Workshop edition:14 location:Copenhagen, Denmark date:15-17 April 2015
Malto-oligosaccharides have high potential as food ingredient, due to their beneficial effects on the flavour and physico-chemical properties of food products. They have mild sweetness, increase the viscosity and have been suggested to delay the retrogradation of starch. As native starch is only slowly degradable by amylases, the first steps in the conversion of starch are gelatinization and liquefaction of the starch polymers. The obtained maltodextrins can then be used for saccharification, i.e. the further hydrolysis to malto-oligosaccharides. Depending on the properties of the amylases used for saccharification, different malto-oligosaccharide enriched syrups can be obtained. In this study, a maltotriose producing amylase from Microbacterium imperiale and a maltotetraose producing amylase from Pseudomonas stutzeri were used to produce maltotriose and maltotetraose enriched syrups, respectively. The maltotriose producing amylase showed the highest activity around 40 °C and pH 6.5 – 7.5 while this was reached around 50 °C and pH 5.5 – 6.5 for the maltotetraose producing amylase. These data were used to optimize the production of maltotriose and maltotetraose syrups. The highest yields of maltotriose were obtained after incubation of a 20% maltodextrin solution with 5.6 units maltotriose producing amylase / g dry matter (dm) maltodextrin for 36 h at 40 °C and pH 5.5. One enzyme unit is the amount of enzyme that releases 1 µmol reducing sugars per mL from a 1.0% soluble starch solution per min at pH 6.0 and 40 °C. Incubation of a 20% maltodextrin solution with 3.5 units maltotetraose producing amylase / g dm maltodextrin for 28 h at 50 °C and pH 5.5 gave the highest yields of maltotetraose. The obtained syrups were further enriched in maltotriose or maltotetraose in one step by size exclusion chromatography (SEC) and collecting specific fractions, or in two steps by selective fermentation of glucose, maltose (and maltotriose) in the syrups with specific yeast strains and ethanol precipitation to remove larger glucose chains. SEC produces maltotriose and maltotetraose of high purity, but the yields are low. It was possible to selectively ferment glucose and maltose (for the maltotriose enriched syrup) and glucose, maltose and maltotriose (for the maltotetraose enriched syrup) by making use of two different Saccharomyces cerevisiae yeast strains. Next to that, larger glucose chains can be removed with ethanol precipitation. Under the experimental conditions, an ethanol concentration of 60% was necessary to precipitate large glucose chains without precipitation of maltotriose and maltotetraose.