The aim of the study was to evaluate the conditions of fermentation pH and temperature and also the fermentation time of Lactobacillus casei in the cupuassu (tropical fruit native to the Brazilian Amazon) beverage. The sugars, organic acids, and antioxidant activity during the fermentation also were investigated. The sensory characteristics were also evaluated. Moreover, the effect of expectation on the acceptability of probiotic and symbiotic cupuassu beverages was rated under three conditions. The blind (consumers were informed that the samples were probiotic and symbiotic beverages and they tasted them); expected (only nutritional claims in short text were informed) and informed (consumers were asked to evaluate the product when they had nutritional information). The conditions for probiotic beverage production were initial pH5.8, the temperature of 30°C, and 18h of fermentation. L. casei had viability higher than 9.34LogCFU/mL with 18h of fermentation. The fructose was the most consumed sugar (84.76%), followed by sucrose (62.10%) and glucose (34.52%). The antioxidant activity increased during the fermentation. The organic acids present in the cupuassu (citric, ascorbic and quinic acids) also supported L. casei growth, being consumed during the fermentation improving the nutritional value of the beverage. The acceptance of the probiotic drink increased when the juice was presented to the informed tasters. Therefore, the nutrition claims were effective in increasing the acceptance. The probiotic cupuassu beverage was well accepted as an alternative functional food. Display omitted •The cupuassu is a good substrate for probiotic growth, with viability higher than 8LogCFU/mL.•The probiotic cupuassu beverage has good sensory acceptance.•The nutritional information increases the acceptance of probiotic cupuassu beverage.•The fermentation with Lactobacillus casei provides increase of the antioxidant activity in cupuassu beverage.