Growth Study, Metabolite Development, and Organoleptic Profile of a Malt-Based Substrate Fermented by Lactic Acid Bacteria

The objective of this study was to investigate the fermentation of barley malt extract by four different lactic acid bacteria (LAB) species and to analyze the effect on biological, physicochemical, and organoleptic attributes of the resulting beverages. Malt and wort were analyzed following the Methodensammlung der Mitteleuropaischen Analysenkommission (MEBAK). Sugars and organic acids were evaluated using HPLC, while aroma compounds and ageing indicators were quantified using a head-space GC-FID. Unhopped wort was able to support the growth of all LAB during the whole experiment time (120 hr), with a cell count increase up to 3.63 log orders. The strain-specific preferences for carbon and nitrogen sources led to significant differences in the accumulation of metabolic byproducts (i.e., organic acids and flavor-active compounds released in the medium). LAB fermentation lowered the amount of some Strecker-aldehydes (2- and 3-methylbutanal and 2-phenylacetaldehyde) carrying "malty" off-flavors and increased dairy-related aroma compounds such as diacetyl and acetoin ("buttery"). The fermented samples were sensorially distinct and described with "bready", "yeasty", "yogurty", or "honey" attributes. In general, LAB fermentation conferred flavor complexity to wort. Forced ageing of the fermented samples led to a large increase of "staling" indicators but these samples improved organoleptic stability compared with the unfermented control

Antifungal activities of three different Lactobacillus species and their production of antifungal carboxylic acids in wheat sourdough

This study was undertaken to assess the antifungal performance of three different Lactobacillus species. Experiments were conducted in vitro and in situ to extend the shelf life of wheat bread. Standard sourdough analyses were performed characterising acidity and carbohydrate levels. Overall, the strains showed good inhibition in vitro against the indicator mould Fusarium culmorum TMW4.2043. Sourdough bread fermented with Lactobacillus amylovorus DSM19280 performed best in the in situ shelf life experiment. An average shelf life extension of six more mould-free days was reached when compared to the non-acidified control bread. A range of antifungal-active acids like 3-phenyllactic acid, 4-hydroxyphenyllactic acid and 2-hydroxyisocaproic acid in quantities between 0.1 and 360 mg/kg were present in the freeze-dried sourdoughs. Their concentration differed greatly amongst the species. However, a higher concentration of these compounds could not completely justify the growth inhibition of environmental moulds. In particular, although Lb. reuteri R29 produced the highest total concentration of these active compounds in the sourdough, its addition to bread did not result in a longest shelf life. Nevertheless, when the artificial compounds were spiked into a chemically acidified dough, it succeeded in a longer shelf life (+25 %) than achieved only by acidifying the dough. This provides evidence of their contribution to the antifungal activity and their synergy in concentration levels far below their single minimal inhibition concentrations under acidic conditions