The plant-based beverage market is currently one of the fastest growing food segments in the world; therefore, there is a need to expand their assortment and production methods to meet the growing demands of consumers. In the production of plant-based beverages, treatments analogous to those used in milk, e.g. fermentation, are increasingly used. The use of fermentation can improve the nutritional properties of the final product and allows to obtain a completely new range of products with specific sensory properties. Propionibacterium are gram-positive mesophilic rods that grow at temperatures of 25-45 °C. These bacteria are capable of biosynthesis of propionic acid and are therefore called propionic fermentation bacteria - PAB. PABs were used in food biotechnology mainly for the production of Swiss-type cheese.
This study aimed to determine the effect of propionic fermentation on the content of selected carbohydrates and B vitamins in plant-based beverages (bean-based and millet-based beverages). The study material consisted of millet- and bean-based beverages obtained in laboratory and lyophilisated starter cultures of Propionibacterium freudenreichii subsp. shermanii PS-4, Propionibacterium freudenreichii subsp. shermanii PD and Propionibacterium freudenreichii subsp. shermanii PP. The content of selected carbohydrates (fructose, glucose, sucrose) and selected B vitamins (B12 and B3) was determined using high performance liquid chromatography (HPLC). The obtained results were statistically analyzed using an univariate analysis of variance ANOVA (p <0.05).
The study showed no common trend of changes in the content of carbonhydrates and B vitamins in the studied plant-based beverages fermented by propionic bacteria strains. Compared to the bean-based beverage, the overall carbohydrate content was lower in the millet-based beverage. Both decrease and increase in the content of individual carbohydrates were observed as a result of the fermentation process. It can be assumed that the observed changes are the result of the selective fermentation of carbohydrates by the propionic bacteria strains used, as well as the increase in the content of monosaccharides as a result of the degradation of oligo- and polysaccharides by bacterial enzymes. In the case of the bean-based beverage, the content of vitamin B12 was significantly reduced after the fermentation process, which could be due to light sensitivity and instability of this vitamin. In the millet-based beverage, the vitamin B12 content was almost doubled in beverages fermented with the use of P. freudenreichii subsp. shermanii PP and P. freudenreichii subsp. shermanii PD, which may indicate that it has been synthesized. The time of the fermentation process as well as conditions and storage time of samples could have influenced the results obtained. The fermentation time may have turned out to be too short to multiply a sufficiently large cell biomass. It is necessary to repeat the study using a longer fermentation time (e.g. 10 hours) and marking additional carbohydrate types (e.g. maltose, galactose, starch).