Changes in Physical and Chemical Parameters of Beetroot and Carrot Juices Obtained by Lactic Fermentation

Fermented foods have gained popularity recently, especially lactofermented vegetable juice products that provide a rich source of nutrients. This study analyzed the properties of fermented beetroot, carrot and beetroot-carrot juices fermented with bacterial strains Lactiplantibacillus plantarum or Levilactobacillus brevis. Density, extract, dry matter content, pH, total acidity, pigments (betalain or carotenoids), color and LAB count were measured. The results showed that the LAB strains used were capable of fermenting the analyzed juices. It was proven that Lactiplantibacillus plantarum was the better strain for fermentation of vegetable juice. This might have been influenced by the fermentation temperature and the duration time. The highest number of lactic acid bacteria was observed for carrot juice fermented with L. brevis on the 4th day (9.41 log CFU/mL), while for L. plantarum the highest numbers were observed on the 5th–6th day (8.9–9.1 log CFU/mL). For beetroot and its mixture with carrot juices, higher results were observed on the 5th day for L. plantarum (9.0 and 8.3 log CFU/mL, respectively). In most variants of this process, fermentation can be completed after 4–5 days. During the fermentation of carrot and mixed juice slow degradation of carotenoids was observed, while in mixed juice an increase of red pigment (betanin) was observed. In beetroot juices huge degradation was observed for fermentation with L. brevis, while the second bacteria kept the same level of red pigment almost until the last day, while yellow decreased from the 3rd day. It can be concluded that the mixed juice was most stable according to the bacteria count and the pigment content. In our opinion, L. plantarum was better for the fermentation of juices than L. brevis. However, in future tests the time of fermentation can be shortened to 5 days and other LAB strains can be tested.