Probiotics remains a major growth market. The European sector is set to more than triple in value over the next few years, according to Frost & Sullivan, to reach $137.9 million (€118.5m) in 2010.
Researchers from the Agricultural University of Athens screened 29 different strains of Lactobacillus from diverse dairy sources, such as raw cow's milk, feta cheese and brine, cheddar cheese and sour milk.
The in vitro studies, published in the March issue of the International Dairy Journal (Vol. 16, pp. 189-199), tested the stability and resistance of the strains to low pH (acidic conditions), bile salt hydrolysis, and antibiotics. The tests were in-line with guidelines from the FAO/WHO selection criteria for candidate probiotics.
"For the selection of highly potent probiotic strains, safety and functionality properties such as antibiotic resistance, adhesion to intestinal cell lines, antimicrobial activity and inhibition of pathogenic adhesion, as well as immunomodulation potential, are highly important and should be studied using reliable in vitro screening methods," explained lead author Petros Maragkoudakis.
All 29 strains survived at pH 3 but only six kept their viability after one hour at pH1. Although this appeared to limit the list of potentials, most probiotic bacteria are consumed along with milk proteins, which are said to protect the bacteria against the acidity found in the human stomach.
When tested for haemolytic activity, or the activity to breakdown red blood cells, 25 strains were classified as gamma-haemolytic, which means they did not cause haemolysis and are thus safe.
Adhesion of the bacteria to the intestinal wall has been claimed to be essential for positive probiotic action. The greatest adhesion was found (25.5 per cent) for the strain L. plantarum ACA-DC 146 extracted from feta brine.
This adhesion to cells is also important because it stops pathogens like E. coli and Salmonella from adhering to the intestinal walls and colonisation by harmful bacteria.
L. plantarum ACA-DC 146 inhibited E. coli adhesion by 40 per cent, but stopped Salmonella typhimurium by only 14 per cent. The best "all-rounder" was L. paracasei subspecies tolerans ACA-DC 4037 which inhibited E. coli and Salmonella by 35 and 28 per cent, respectively.
When taken altogether, the data show that L. plantarum ACA-DC 146 and L. paracasei subspecies tolerans ACA-DC 4037 (extracted from Kaseri cheese), along with L. casei Shirota ACA-DC 6002 from Yakult possess desirable probiotic properties.
"These strains are good candidates for further investigation in in vivo studies to elucidate their potential health benefits and their application as novel probiotic strains in the food industry," concluded Maragkoudakis.
Co-researcher Georgia Zoumpopoulou told NutraIngredients.com that the good potential from in vitro study is the first step in the development of new probiotics.
"The next step is to go and check in vivo to see if the results continue to be the same," said Zoumpopoulou. "But no trials have been planned yet."
Financial support came from the Greek General Secretariat of Research and Technology. The researchers declared no industrial financial support.