Due to the popularization of the „Super Food” trend, consumers expect the presence in the market of products with a broad spectrum of impact on the human body. The goji berry juice is characterized by many beneficial properties, and enriching it with potentially probiotic strains of Lactobacillus spp. can further enhance its nutritional value provided the strains remain viable. The objective of the research study was to identify and evaluate the physiological activity of Lactobacillus spp. in goji berry juice using a fluorescent in situ hybridization (FISH) method. In order to identify Lactobacillus spp., the in situ hybridization was conducted with rRNA oligonucleotide probes including the domain-specific probe Eubacteria (Eub338), the nonsense probe (Non338), the probes specific for lactic acid bacteria (Lab158) group as well as 11 species-specific probes for different Lactobacillus species. The analysis of the physiological activity of Lactobacillus spp. cells in goji berry juice was carried out using the probe Eub338 immediately after the inoculation and on the 3^rd, 8^th, 15^th, 22^nd, and 29^th day of storage at a 20 ºC (± 2 ºC) and at 6 ºC; the analysis results were compared with the results of the plate count method. The FISH method made it possible to determine the species where 8 out of 9 strains tested belonged to; those bacteria were classified as L. plantarum and L. brevis. In addition, it was proved that the physiological activity of the cells underwent significant changes resulting from storing the goji berry juice at a 20 ºC (± 2 ºC), i.e. it decreased on the last day of storage. Comparing those results with the results of the plate method, the non-culturability of the cells may be suggested. However, after storing the juice at 6 ºC, its physiological activity was stable as the cell count was high until the last day of storage. Research conducted in this area indicates that the
FISH method is useful for detecting and analyzing the physiology of Lactobacillus spp.