Survival of probiotic lactobacilli in the upper gastrointestinal tract using an in vitro gastric model of digestion.

The aim of this study was to investigate survival of three commercial probiotic strains (Lactobacillus casei subsp. shirota, L. casei subsp. immunitas, Lactobacillus acidophilus subsp. johnsonii) in the human upper gastrointestinal (GI) tract using a dynamic gastric model (DGM) of digestion followed by incubation under duodenal conditions. Water and milk were used as food matrices and survival was evaluated in both logarithmic and stationary phase. The % of recovery in logarithmic phase ranged from 1.0% to 43.8% in water for all tested strains, and from 80.5% to 197% in milk. Higher survival was observed in stationary phase for all strains. L. acidophilus subsp. johnsonii showed the highest survival rate in both water (93.9%) and milk (202.4%). Lactic acid production was higher in stationary phase, L. casei subsp. shirota producing the highest concentration (98.2 mM) after in vitro gastric plus duodenal digestion.

Survival of Lactobacillus rhamnosus strains in the upper gastrointestinal tract.

In the present study six probiotic Lactobacillus rhamnosus strains were investigated for their ability to survive in the human upper gastrointestinal tract through a dynamic gastric model of digestion. MRS broth was used as delivery vehicle and survival was investigated during in vitro gastric and gastric plus duodenal digestion. Results highlighted that all tested strains showed good survival rate during both gastric and duodenal digestion. In particular, three strains exhibited a great survival showing a recovery percentage in the range between 117 and 276%. In agreement with survival data, high lactic acid production was detected for all strains, confirming their metabolic activity during digestion.

Challenges to understanding and measuring carotenoid bioavailability.

Carotenoids are an excellent example of where poor understanding of food structure, complexity of behaviour during digestion, and inter-individual differences in response, lead to misinterpretation of study results. Four challenges associated with understanding and measuring carotenoid bioavailability are discussed: release of carotenoids from food structure and processing into an absorbable form (bioaccessibility), passage of carotenoids from gut lumen into the body (absorption), interpreting plasma response and inter-individual variation. Bioaccessibility of carotenoids is governed by characteristics of the food matrix, which affect the efficiency of physical, enzymic and chemical digestion. Carotenoids used as colorants are likely to be better absorbed because of the form in which they are dispersed in food. Extent of absorption of carotenoid supplements will depend on the proximity of dosing to the consumption of a fat-containing meal. Release of carotenoids from food plants occurs only when the plant cell is fractured and this occurs only during food preparation, processing and/or mastication, not during digestion. Following release from the food matrix, the major limiting factor is solubility of carotenoids in digesta. Absorption studies are best carried out by measuring chylomicron carotenoid excursion, with modelling of chylomicron turnover rate. In this way, inter-individual differences in lipoprotein metabolism can, in part, be taken into account before formulating conclusions on the rate and extent of absorption.