The number of people who cannot consume dairy products due to intolerance or allergies to food components is increasing. Consumers are increasingly searching for alternative, nondairy beverages which have an advantageous effect on the body and which stimulate gut microflora. Previous studies have shown that Streptococcus thermophilus TKM3 KKP 2030p can be an efficient starter culture for the fermentation of plant material and can also ensure an acceptable sensory profile and a high number of lactic acid bacteria during 4 week cold storage. The aim of this study was to determine the relative gene expression of the l-lactate dehydrogenase gene (ldhL) in selected strain using the RT qPCR technique at particular time points. The gene expression experiments were conducted in laboratory broth (LABm) and fruit-cereal (OBPromOat) matrix with a beta-glucan additive. Levels of gene relative expression in the selected strain in these two media were correlated with the amount of l-lactate produced. The results showed that the plant matrix stimulated stronger ldhL gene expression in the first 4 h of the experiment (although the synthesis of l-lactate was less than in laboratory broth). This study broadens existing knowledge of the transcriptional mechanisms which arise from the adaptation of the analyzed strain to different habitats during l-lactate synthesis. This could contribute to the development of new alternative food products for people who show intolerance to milk proteins or lactose.