Objective. Evaluate lacto-serum as a source of mesophils with lactic acid activity in complex culture medium with sago starch (Canna indica L.). Materials and methods. Three culture media were analyzed for mesophilic lacto-serum bacteria differentiated by the inclusion of sago starch (Canna indica L.) (0, 0.5 and 1%). Control treatments were refrigerated (-4°C) and non-refrigerated (18°C) lacto-serum. Mesophilic growth, pH, acidity level, and total soluble solids were evaluated at 24 h intervals for 5 days; and lactic acid concentration at the end of the test. Results. The pH and total soluble solids (°Brix) decreased in all treatments, the % acidity increased over time and at the end of the trial the highest content of lactic acid was 32.5 and 37.2 g / L for the formulations with 0.5 and 1% sago starch respectively. Mesophilic growth was low in the 1% starch formulation and high in the non-refrigerated serum. Conclusion. Lacto-serum is a good source of mesophiles with lactic acid activity, reaching up to 37.2 g/L lactic acid in complex culture medium including 1% sago starch.