Koumiss is a slightly alcoholic fermented milk beverage, originally obtained by using natural mix starters (lactic acid bacteria and yeast). Seven Lactobacillus strains from lyophilized koumiss were isolated and identified as L. salivarius, L. buchneri and L. plantarum. The process of lactic acid fermentation caused by koumiss strains was faster (9–13 h) than that with other lactobacilli. The conversion ratio of glucose to lactic acid ranged from 47% to 79% and was strain dependent. All strains were resistant to low pH. Three of the strains isolated were viable during prolonged cold storage in fermented milk (3 weeks at 4°C).

The glycerol fermentation by Klebsiella pneumoniae occurs by receiving more than five liquid products-organic acids, diols, and ethanol. Aiming to direct the glycerol conversion towards predominant production of 2,3-butanediol (2,3-BD), the main influencing parameters (the aeration and the pH) were investigated during fed-batch processes. The regime of intensive aeration (2.2 vvm air supply) was evaluated as most favorable for 2,3-BD synthesis and ensured the decrease of all other metabolites. Thus, without pH control, 52.5 g/l 2,3-BD were produced, as the carbon conversion of glycerol into 2,3-BD reached 60.6%. Additional enhancement in 2,3-BD production (by significant increase of glycerol utilization) was achieved by the development of a new method of "forced pH fluctuations". It was realized by consecutive raisings of pH using definite DeltapH value, at exact time intervals, allowing multiple variations. Thus, the optimal conditions for maximal glycerol consumption were defined, and 70 g/l 2,3-BD were produced, which is the highest amount obtained from glycerol as a sole carbon source until now. The forced pH fluctuations emphasized pH as a governing factor in microbial conversion processes.

The microbial production of high amounts of 2,3-butanediol (2,3-BD) from glycerol as a sole carbon source by the Bulgarian isolate Klebsiella pneumoniae G31 was studied in a series of fed-batch processes. The following conditions were evaluated as optimal: micro-aerobic cultivation in modified media, without pH control. Beginning at pH 8, 49.2 g/l of 2,3-BD was produced as negligible concentrations of by-products were received. The pH is the most important factor ruling the 2,3-BD production. Spontaneous pH changes and products formation in time were investigated, performing fermentations with non-controlled pH starting at different initial pH. In lack of external maintenance, the microorganism attempted to control the pH using acetate/2,3-BD alternations of the oxidative pathway of glycerol catabolism, which resulted in pH fluctuations. Thus, the culture secreted 2,3-BD at unequal portions, either allowing or detaining the acetate synthesis. More alkaline initial pH led to enhanced 2,3-BD accumulation as a response to the increased amplitudes of the pH variations. When the pH was maintained constant, the yield of 2,3-BD was very poor. These cultures remained viable only 72 h; whereas, the pH self-controlling cells lived and produced 2,3-BD up to 280 h. In conclusion, the formation of 2,3-BD is a result of an adaptive mechanism of pH self-control, responding to spontaneous pH drops during glycerol fermentation.

Grains are a substantial source of macronutrients and energy for humans. Lactic acid (LA) fermentation is the oldest and most popular way to improve the functionality, nutritional value, taste, appearance and safety of cereal foods and reduce the energy required for cooking. This literature review discusses lactic acid fermentation of the most commonly used cereals and pseudocereals by examination of the microbiological and biochemical fundamentals of the process. The study provides a critical overview of the indispensable participation of lactic acid bacteria (LAB) in the production of many traditional, ethnic, ancient and modern fermented cereals and beverages, as the analysed literature covers 40 years. The results reveal that the functional aspects of LAB fermented foods are due to significant molecular changes in macronutrients during LA fermentation. Through the action of a vast microbial enzymatic pool, LAB form a broad spectrum of volatile compounds, bioactive peptides and oligosaccharides with prebiotic potential. Modern applications of this ancient bioprocess include the industrial production of probiotic sourdough, fortified pasta, cereal beverages and “boutique” pseudocereal bread. These goods are very promising in broadening the daily menu of consumers with special nutritional needs.

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