Lactobacillus rhamnosus GG is an industrially significant probiotic strain with proven health benefits. In this study, the effect of glucose on L. rhamnosus GG survival was analyzed in simulated gastric juice at pH 2.0. It was found that the presence of 19.4 mM glucose resulted in up to 6-log 10 -enhanced survival following 90 min of exposure. Further work with dilute HCl confirmed that glucose was the sole component responsible. Comparative analysis with other Lactobacillus strains revealed that enhanced survival was apparent in all strains, but at different pH values. The presence of glucose at concentrations from 1 to 19.4 mM enhanced L. rhamnosus GG survival from 6.4 to 8 log 10 CFU ml ؊1 in simulated gastric juice. The mechanisms behind the protective effect of glucose were investigated. Addition of N,N-dicyclohexylcarbodiimide to simulated gastric juice caused survival to collapse, which was indicative of a prominent role in inhibition of F 0 F 1 -ATPase. Further work with neomycin-resistant mutants that exhibited 38% to 48% of the F 0 F 1 -ATPase activity of the parent confirmed this, as the survival in the presence of glucose of these mutants decreased 3 ؋ 10 6 -fold compared with the survival of the wild type (which had a viability of 8.02 log 10 CFU ml ؊1 ). L. rhamnosus GG survival in acidic conditions occurred only in the presence of sugars that it could metabolize efficiently. To confirm the involvement of glycolysis in the glucose effect, iodoacetic acid was used to inhibit glyceraldehyde-3-phosphate dehydrogenase (GAPDH) activity. The reduction in GAPDH activity caused survival to decrease by 8.30 log 10 CFU ml ؊1 in the presence of glucose. The data indicate that glucose provides ATP to F 0 F 1 -ATPase via glycolysis, enabling proton exclusion and thereby enhancing survival during gastric transit.

Aims: Probiotic milk-based formulations were spray-dried with various combinations of prebiotic substances in an effort to generate synbiotic powder products. Methods and Results: To examine the effect of growth phase and inclusion of a prebiotic substance in the feed media on probiotic viability during spray-drying, Lactobacillus rhamnosus GG was spray-dried in lag, early log and stationary phases of growth in reconstituted skim milk (RSM) (20% w/v) or RSM (10% w/v), polydextrose (PD) (10% w/v) mixture at an outlet temperature of 85-90°C. Stationary phase cultures survived best (31-50%) in both feed media and were the most stable during powder storage at 4-37°C over 8 weeks, with 30-140-fold reductions in cell viability at 37°C in RSM and PD/RSM powders, respectively. Stationary phase Lact. rhamnosus GG was subsequently spray-dried in the presence of the prebiotic inulin in the feed media, composed of RSM (10% w/v) and inulin (10% w/v), and survival following spray-drying was of the order 7AE1-43%, while viability losses of 20 000-90 000-fold occurred in these powders after 8 weeksÕ storage at 37°C. Survival of the Lactobacillus culture after spray-drying in powders produced using PD (20% w/v) or inulin (20% w/v) as the feed media was only 0AE011-0AE45%. To compare different probiotic lactobacilli during spray-drying, stationary phase Lact. rhamnosus E800 and Lact. salivarius UCC 500 were spray-dried using the same parameters as for Lact. rhamnosus GG in either RSM (20% w/v) or RSM (10% w/v) and PD (10% w/v). Lact. rhamnosus E800 experienced approx. 25-41% survival, yielding powders containing 10 9 CFU g )1 , while Lact. salivarius UCC 500 performed poorly, experiencing over 99% loss in viability during spray-drying in both feed media. In addition to the superior survival of Lact. rhamnosus GG after spray-drying, both strains experienced higher viability losses (570-700-fold) during storage at 37°C over 8 weeks compared with Lact. rhamnosus GG.Conclusions: Stationary phase cultures were most suitable for the spray-drying process, while lag phase was most susceptible. The presence of the prebiotics PD and inulin did not enhance viability during spray-drying or powder storage.Significance and Impact of the study: High viability (10 9 CFU g )1 ) powders containing probiotic lactobacilli in combination with prebiotics were developed, which may be useful as functional food ingredients for the manufacture of probiotic foods.

The continuing expansion of interest in probiotic bacteria has led to an increase in manufactured Functional Foods and medicines containing these bacteria. Given the intestinal origin of these microorganisms, the challenges these sensitive bacteria face in order to be in a highly viable state throughout processing, storage and gastrointestinal transit to the site of action in the human gut are enormous. These bacteria encounter stresses including temperature, acid, bile, exposure and osmotic and oxidative stress in both product matrices and during gastrointestinal transit. However, like all bacteria, probiotic bacteria retain a broad arsenal of molecular mechanisms to combat the often lethal environmental stresses encountered during processing and following ingestion. A comprehensive appreciation of these mechanisms should inevitably lead to the design and manufacture of probiotic cultures, which retain greater viability through to the target site in the intestine. This review attempts to catalogue the cellular processes available to probiotic bacteria to facilitate survival in stressful conditions, and to speculate on how manipulation of these cellular systems can lead to production of designer strains with enhanced viability in food systems and efficacy following ingestion.

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