Canadian scientists have reported that two strains of probiotic Lactobacillus bacteria grow well in soy yoghurt cultures, opening up opportunities for an ever growing field.
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.
Most foods containing probiotic bacteria are found in the refrigerated section of supermarkets as the bacteria is destroyed by heat and other processing conditions.
This has given the dairy sector, already used to handling live bacteria for the manufacture of yoghurt, a major advantage in probiotic foods - probiotic drinking yoghurts are currently the fastest growing dairy product in Europe.
"This study is the first report of the potential of L. rhamnosus GG and L. johnsonii La-1 as probiotics in fermented soy products with yogurt cultures. These lactobacilli can compete better with the yogurt strains in a soy beverage than in cows' milk," wrote the researchers from Agriculture and Agri-food Canada, and Quebec's Université Laval.
"Soy-based yogurt containing L. rhamnosus GG and L. johnsonii La-1 are therefore possible," they said.
Yogurt is produced by adding two bacterial starter cultures to milk - Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus - and numerous studies have reported that soy is a good substrate for probiotic bacteria, at the expense of the L. delbrueckii subsp. bulgaricus.
"Unfortunately, little information is available on the growth of probiotic bacteria in mixed cultures with yoghurt strains in soy substrates, because most studies on the growth of probiotics in soy extracts have been carried out using pure cultures," said the researchers.
Writing in the Elsevier journal, the International Journal of Food Microbiology, the researchers report that soy yoghurt the presence of the probiotics Lactobacillus johnsonii NCC533 (La-1, Nestlé) or Lactobacillus rhamnosus ATCC 53103 (GG) did not effect the growth of the starter cultures, with significant increases in bacterial populations observed for both strains.
Depending on whether the strains were in the cows' milk or soy was used, it was found that the probiotic bacteria were using different sugars to support their growth, as determined by high pressure liquid chromatography (HPLC).
Some challenges remain, said the researchers, since the probiotic bacteria levels in the soy products did not reach the set level of 100bn cfu/ml required to produce gastro-intestinal tract health effects.
"Although probiotic bacteria grow in cows' milk and soy substrates, they still remain a minor fraction of the total population when yogurt starters are present. Approaches such as milk supplementation or changes in inoculation levels are available to manufacturers who wish to increase the probiotic bacteria content in their fermented dairy products," wrote the researchers.
"Further studies are needed, however, to determine if these strategies can also be effective with soy-based media."
The study was sponsored by Canada's Institut des Nutraceutiques et des Aliments Fonctionnels (INAF).
Source: International Journal of Food Microbiology
Published on-line ahead of print, doi:10.1016/j.ijfoodmicro.2006.12.015
"Growth of probiotic bacteria and bifidobacteria in a soy yogurt formulation"
Authors: E.R. Farnworth, I. Mainville, M.-P. Desjardins, N. Gardner, I. Fliss and C. Champagne