Incorporate Lactobacillus rhamnosus into yogurt, creating probiotic product

Emerging Food R&D Report, Jan, 2009

Dairy products are able to effectively deliver probiotic microorganisms to consumers. The fermentation of milk into yogurt has gained widespread consumer acceptance in North America. Unfortunately, the usual yogurt cultures, Lactobacillus delbreukii sub-species bulgaricus and Streptococcus thermophilus, are neither bile-resistant nor acid-tolerant. They cannot survive in the intestinal tract, although they may help to lessen the symptoms of lactose intolerance.

But two of the most documented probiotic strains, Lactobacillus reuteri (formerly fermentum) RC-14 and Lactobacillus rhamnosus GR-1, can colonize the intestine and reduce recurrences of bacterial vaginosis, yeast vaginitis and urinary tract infections. They are bile-resistant and survive passage through the human gastrointestinal tract without inducing systemic immune or inflammatory responses.

Canadian researchers have been able to successfully incorporate L. reuteri RC-14 and L. rhamnosus GR-1 into low-fat yogurt, potentially creating a new probiotic product. Viable counts of L. rhamnosus GR-1 were observed after the yogurt was refrigerated for 28 days.

To prepare mother cultures for these bacteria, the researchers made four formulations: 1% milk and 0.33% yeast extract (T1); 0.4% inulin (T2); 0.33% yeast extract and 0.4% inulin (T3); and one formulation with no additives (T4). The media were inoculated with 1% probiotic cultures and incubated anaerobically at 37 C overnight. Low-fat (1%) probiotic yogurts were made.

The survival of L. reuteri RC-14 and L. rhamnosus GR-1 was monitored after 1, 7, 14, 21 and 28 days of storage at 4 C. In all treatments, L. rhamnosus GR-1 survived significantly better than L. reuteri RC-14. Survival was highest in media T1 and T3.

L. rhamnosus GR-1 can provide an excellent shelf life for the product. The scientists found that, in all formulations, GR-1 had significantly better survival rates than L. reuteri RC-14. L. reuteri RC-14 is sensitive to the acidic condition of yogurt, or its viability is adversely affected for other reasons. This poor ability of RC-14 to persist in yogurt is not restricted to this species, as other potential probiotic bacteria have also shown an inability to survive well due to yogurt's intrinsic properties, such as pH and the presence of oxygen.

The scientists have used GR-1 in yogurt in a grass roots humanitarian project in Tanzania and are planning more studies there. They have since developed another yogurt with GR-1 and a Bifidobacterium strain and have shown that it holds promise against allergy. None of these applications has yet been picked up by industry.

Further information. Gregor Reid, The University of Western Ontario, Canadian R&D Centre for Probiotics, F2-116, Lawson Health Research Institute, 268 Grosvenor St., London, Ontario N6A 4V2, Canada; phone: 519-646-6100; fax: 519-646-6031; email: gregor@uwo.ca.