Enzymatic analysis of levan produced by lactic acid bacteria in fermented doughs

•Bacterial levan in situ analyzed by enzymatic hydrolysis for the first time.•Levan content estimated from the sugars released by levanase/exoinulinase action.•Possible interference of plant and bacterial origin identified and corrected.•An endoinulinase treatment introduced to detect the presence of interfering inulin.•Applicability demonstrated for levan in wheat and fava bean dough matrices. Levans and inulins are fructans with mainly β-(2→6) and β-(2→1) linkages, respectively. Levans are produced by many lactic acid bacteria, e.g. during sourdough fermentation. Levans have shown prebiotic properties and may also function as in situ-produced hydrocolloids. So far, levan contents have been measured by acid hydrolysis, which cannot distinguish levans from e.g. inulins. In order to develop a specific analysis for levan in food matrices, a Paenibacillus amylolyticus endolevanase was combined with exoinulinase for levan hydrolysis. A separate endoinulinase treatment was used to detect the possible presence of inulin. Interfering sugars were removed by a pre-wash with aqueous ethanol. Levan content was estimated from fructose and glucose released in the hydrolysis, with a correction made for the residual fructose and glucose-containing sugars. The method was validated using wheat model doughs spiked with commercial Erwinia levan, and tested by analyzing levan content in Leuconostoc mesenteroides DSM 20343-fermented fava bean doughs.