Fermentative in situ synthesis of isomalto/malto-polysaccharides in sourdough

Some sourdough-derived lactic acid bacteria were shown to fermentatively synthesize potentially prebiotic isomalto/malto-polysaccharides (IMMPs) from maltodextrins. Therefore, the application of suitable starter cultures and adjusted fermentation conditions could be used to achieve a fermentative synthesis of IMMPs in sourdough, however, this has not been investigated yet. To monitor in situ IMMP synthesis, a new method based on endo-dextranase hydrolysis and quantification of released isomaltose was developed. Subsequently, it was applied to determine the amount of dextran equivalents (fermentatively formed α-1,6-linkages) in sourdoughs produced under different conditions. Of all seven investigated strains, Limosilactobacillus reuteri TMW 1.106 in combination with the addition of pregelatinized starch and starch-debranching enzymes produced by far the highest amount of IMMPs within 20 h of fermentation. Other changes in fermentation conditions did not significantly increase IMMP formation. However, applying adjusted conditions during sourdough fermentation may be used to increase the amount of potentially prebiotic carbohydrates in bread.