Abstract
In the present study, 33 strains of lactic acid bacteria (LAB) previously isolated from natural black Conservolea olives were assessed for their probiotic potential in vitro, as well as for their autoinducer-2 (AI-2) activity under standard growth conditions and the production of γ-aminobutyric acid (GABA). The probiotic tests included the in vitro resistance to low pH and resistance to bile salts, the evaluation of bile salt hydrolase activity, as well as safety tests regarding their possible haemolytic activity and their antimicrobial activity against pathogens. The results indicated that 17 strains were able to survive in low pH and in the presence of bile, with 15 of them also exhibiting partial bile salt hydrolase activity. None of the strains exhibited haemolytic activity or inhibited the growth of any of the examined pathogens. Moreover, the strains displayed generally low AI-2 activity under the growth conditions tested, regardless of the species. Interestingly, in contrast to what has been found in most foods, none of the isolates were found to produce GABA after 48 h of growth. The results from the AI-2 activity and extracellular GABA detection were considered as unexpected for LAB with probiotic attributes.
Highlights
Lactic acid bacteria (LAB) are the most important group of probiotic bacteria, followed by Bifidobacteria, and some species of Enterococci and Bacillus, the safety of the latter remains a controversy
Results from low pH resistance were in agreement with other studies, where Lactobacillus pentosus and Lactobacillus plantarum strains were able to maintain their viability after exposure to low pH; a variation in the acid resistance among different strains was observed [6,8,10]
A total of 17 strains were chosen as good candidates for potentially probiotic applications, as adjunct or co-starter cultures, more tests are required to further assess their potential as probiotics
Summary
Lactic acid bacteria (LAB) are the most important group of probiotic bacteria, followed by Bifidobacteria, and some species of Enterococci and Bacillus, the safety of the latter remains a controversy. Many beneficial effects of probiotics have been associated with lowering of cholesterol, controlling symptoms of lactose intolerance, stimulating the immune system, relieving constipation, preventing antibiotic-associated and traveller’s diarrhoea, and prevention of Clostridium difficile infections [1,2,3,4,5]. Such bacteria have been isolated from various sources, including fermented dairy products [6,7], non-dairy products [8,9,10,11,12], and from the intestinal tract of healthy individuals or infants [13,14,15]. Such tests could include acid and bile resistance, the production of
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