One of the most important parameters influencing the development of probiotic foods is the viability of probiotic cells, which depends on numerous secondary elements: optimal growth and survival during food processing; storage; transit through the gastrointestinal tract; adherence to the intestinal epithelium; antimicrobial properties; and antibiotic resistance (21). In addition, probiotic microorganisms must remain viable during large-scale production and incorporation into food products without loss of functionality (16).
The main bacterial genera considered for use as probiotics are Lactobacillus and Bifidobacterium, which can be incorporated into foods alone or in combination. According to Brazilian legislation, to produce beneficial effects, probiotic bacteria must be viable, with a concentration between 108 and 109 CFU/g product, and their consumption should be associated with a balanced diet and healthy lifestyle (2). Several functional properties associated with Gram-positive lactobacillus L. rhamnosus have been reported in the literature, including: an anti-obesity effect (18), gastrointestinal tract colonisation (15, 17), enhanced immunity (22), anti-inflammatory bowel disease (IBD) effects (5); and anti-carcinogenic effects (13).
However, milk fermentation by one or more probiotic species requires a long incubation period, resulting in a low-quality product; thus, probiotics are generally produced in association with a yogurt starter culture. Yogurt is traditionally obtained by fermentation of a starter culture composed of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus (22).
The viability of probiotic bacteria is mainly affected by competition with other contaminating microorganisms. Thus, it is important that undesirable cells be inactivated, without interfering with the development of beneficial bacteria (16).
The addition of essential oils (EOs) to foods has aroused great interest, because of their antagonistic action against pathogenic and spoilage microorganisms. This action, however, may affect probiotic bacteria in probiotic containing foods. Thus, the present study aimed to determine the antimicrobial activity of cinnamon, clove and mint EOs (at the maximum accepted concentration, based on a previous sensory analysis) against Lactobacillus rhamnosus and a yogurt starter culture, during the shelf-life period of fermented milk. In addition, in vitro assays were conducted to obtain the Minimal Inhibitoiy Concentration (MIC).