Components of a Synthetic Cucumber Juice Medium Influencing the Growth and Metabolism of Lactiplantibacillus Species

A semi-defined cucumber juice medium (ACJ30) was prepared that had similar buffering capacity, nutrients and chemical components as a natural cucumber juice medium (CJ). The medium was designed to closely match the growth kinetics, pH evolution and fermentation chemistry typical for lactic acid bacteria (LAB) found in commercial cucumber fermentations. In this study the ACJ30 fermentation model system was used to determine how specific medium components could influence the growth, pH and acid production of Lactiplantibacillus pentosus LA445 and other LAB. By varying selected non-buffering components of ACJ30, including Tween 80® (as a source of oleic acid), and manganese concentrations, the growth rates, final cell density, and fermentation acid production could be varied by 50% or greater. Removing malic acid (typically at 9 mM in brines at the start of cucumber fermentations) from the ACJ30 medium resulted in significantly lower final pH and limited cell growth for LA445 (log 10 7.9 vs. log 10 9 CFU/mL), as well as reduced lactic acid production 33.9 +/- 3 mM at 72 h compared to 70 to 90 mM with either L-malic acid or non-metabolizable D-malic acid. These data indicate that malic acid buffering was an important factor for cell growth and acid production. The ACJ30 model fermentation system may be easily modified to study other types of vegetable fermentations. Similar model fermentation systems may be used to help determine the influence of medium components on cell growth, acid production, pH evolution, and therefore the quality and safety of a variety of fermented foods.