Resumo

The resistance to simulated gastric digestion is an easy-to-apply in vitro tool that may contribute to product design and may help in the choice of the food matrix when no changes in cell viability are observed along storage. Moreover, probiotic viability is essential to assure product’s functionality to the host. This study aimed to investigate the influence of different fermented milk matrices on resistance to simulated gastrointestinal conditions of Streptococcus thermophilus and Bifidobacterium lactis. Three milk matrices where prepared. Two matrices enriched with passion fruit peel powder and fat from milk cream or from vegetal oil emulsion and one not enriched matrix that was used as control. All products had similar energetic content and macronutrient composition in order to provide similar fermented milks in aspect, flavour and consistence. Fermentation was performed by a co-culture of Streptococcus thermophilus (TA040) and Bifidobacterium lactis (Bifidobacterium species 420B) at 37 °C until pH 4.7 in industrial scale. Products, after seven and 28 days of cold storage, were submitted to an in vitro methodology which mimics in vivo human upper gastrointestinal transit considering esophagus-stomach (artificial gastric juice), duodenum (artificial intestinal juice) and ileum. Counts of viable cells were similar and higher than 8.5 Logcfu.mL-1 in all products during cold storage. After simulated gastric digestion no viable cells of Streptococcus thermophilus (TA040) were detected. Esophagus-stomach, duodenum and ileum conditions decreased viable numbers of B. lactis accordingly to matrix and storage time. The source of the fat interferes significantly with the survival of Bifidobacterium lactis during transit. Finally, other methodologies as well as further tools as dynamic simulated gastrointestinal conditions should be applied to study probiotic survival in food matrices. Besides, technological changes and product development can be carried out in order to make a strain adapted for other food matrices.