Your stomach is built to kill bacteria. Ours get through.
Shop shielded probioticsStomach acid is the single biggest reason probiotics fail. Two peer-reviewed studies put micro-shielded Velobiotics™ bacteria through simulated stomach acid and intestinal fluid. Here is what came out the other side.
The short version
- Researchers exposed bacteria to simulated stomach acid (pH 2) for two hours, then simulated intestinal fluid (pH 6.8) for up to 24 hours, the same sequence food follows in your body.
- Unprotected bacteria lost numbers steadily. Micro-shielded bacteria released nothing in the acid, then released high numbers of live cells in the intestinal fluid.
- Across the trials, shielding delivered on average 1.6 to 1.8 log more live bacteria, which is 40 to 65 times more survivors.
- The protection still worked after seven weeks of storage at 30 °C: unprotected bacteria were all killed by the acid; shielded bacteria came through and were released alive.
What happens to a probiotic after you swallow it
Your stomach holds hydrochloric acid at roughly pH 1.5 to 2. It exists to break down food and destroy the bacteria that arrive with it. It does this job very well. Studies on ordinary bifidobacteria report losses of 3 to 4 log, that is 99.9% to 99.99% of the cells, within two hours of stomach-strength acid.
Only the survivors move on into the small intestine, where the pH climbs to about 6.8 and bile adds a second challenge. Whatever is still alive after that can finally attach to the gut wall, multiply and do the work you bought the probiotic for.
A stomach and intestine in the lab
Scientists at the University of Pretoria and the CSIR reproduced this journey in the laboratory. Micro-shielded Bifidobacterium longum Bb-46 and unprotected cells of the same strain were placed in simulated gastric fluid at pH 2 for two hours, then transferred to simulated intestinal fluid at pH 6.8 for six or 24 hours, all at body temperature. At each step they counted the live bacteria.
Two results stood out. While in the acid, the shielded sample released no live bacteria at all: the coat stayed sealed. Once in the intestinal fluid, the coat swelled and released about 9 log (a billion) live cells per gram after 24 hours. The unprotected bacteria, meanwhile, kept declining.
Simulated gastric fluid at pH 2 and 37 °C, mimicking a meal's time in the stomach.
Simulated intestinal fluid at pH 6.8 and 37 °C, where the shield is designed to dissolve.
Samples plated on agar and grown for 72 hours without oxygen; each colony is one bacterium that was alive.
“PVP:VA-CA completely protected the bacteria during exposure to SGF. An increase in the numbers of viable bacteria released from the interpolymer complex indicated efficient release properties of the complex at higher pH values.”
— Thantsha, Cloete, Moolman & Labuschagne, International Journal of Food Microbiology, 2009
Two refinements that improved protection further
The team then tested variations. Adding glyceryl monostearate (GMS), a digestible lipid that resists acid, moisture and oxygen, significantly increased the number of live bacteria released; raising the GMS content from 8% to 60% improved protection again. Enclosing the shielded powder in a standard gelatine capsule delayed any release in acid by a further hour, adding a second line of defence. Both refinements are part of how Velobiotics™ products are formulated today.
It still works after months on the shelf
A probiotic that survives acid on the day it is made is not enough; it has to survive acid after months in a warehouse and a bathroom cabinet. So the researchers stored the shielded bacteria at 30 °C for seven weeks and repeated the test.
The unprotected bacteria that were still alive after storage were all killed by the acid. The shielded bacteria released nothing in the acid and then released high numbers of live cells in the intestinal fluid. The shield protected them twice: on the shelf and in the stomach.
The science in detail
Methods, formulations and the exact numbers, for readers who want them.
Study design and counting method
Simulated gastric fluid (SGF, pH 2) was prepared after Lian et al.; simulated intestinal fluid (SIF, pH 6.8) followed the US Pharmacopeia. One gram of product was exposed sequentially to SGF for 2 h and SIF for 6 or 24 h at 37 °C. Total encapsulated bacteria were determined by suspending 1 g in SIF for 6 h before plating. Counts were made in triplicate on MRS agar with 0.05% cysteine-HCl, incubated anaerobically at 37 °C for 72 h. In the 2009 paper the average improvement in survival for encapsulated versus free B. longum Bb-46 was 1.61 ± 0.49 log CFU/g (p < 0.05, n = 18); in the 2006 paper, across four SGJ/SIF trials, 1.81 ± 0.56 log CFU/g (p < 0.05).
Formulations tested, and which ones failed
The basic PVP:VA-CA matrix protected completely in acid and released well in SIF. Adding the copolymer PEO-PPO-PEO made the matrix swell in acid and reduced protection (p = 0.170, not significant). Replacing PVP with polycaprolactone (PCL) also performed worse than unprotected cells. GMS at 8% significantly improved survival (p = 0.045) and 60% GMS improved it further; gelatine capsules delayed release in SGF by 30 min (free cells) and 60 min (shielded cells). The authors noted batch-to-batch variation in the basic system (−0.28 vs −2.96 log in two batches), which the GMS formulation reduced. Velobiotics™ uses the GMS-strengthened matrix.
Storage-then-acid test
Shielded and unprotected B. longum Bb-46 were stored at 30 °C for seven weeks, then exposed to SGF and SIF. Viable counts in diluent were higher for shielded cells after storage. Unprotected cells that survived storage gave no counts after SGF and SIF. Shielded cells released no cells in 2 h of SGF and high numbers of viable bacteria in SIF, showing protection both in transit and during storage (Thantsha et al. 2009, Fig. 3).
References
- Thantsha MS, Cloete TE, Moolman FS, Labuschagne PW. Supercritical carbon dioxide interpolymer complexes improve survival of B. longum Bb-46 in simulated gastrointestinal fluids. International Journal of Food Microbiology 2009;129:88–92. PDF
- Moolman FS et al. Encapsulating probiotics with an interpolymer complex in supercritical carbon dioxide. South African Journal of Science 2006;102:349–354. PDF
- Hansen TL et al. Survival of Ca-alginate microencapsulated Bifidobacterium spp. in milk and simulated gastrointestinal conditions. Food Microbiology 2002;19:35–45 (reference for 3–4 log losses of unprotected B. longum Bb-46 in 2 h of SGF).
The rest of the science, in order
Seven short pages. Start anywhere; each one stands on its own.
A father, a hospital bed, and the question that started everything.
View →2Why most probiotics failHeat, humidity, acid and bile: the five challenges a probiotic must survive.
View →3What is microencapsulation?Each bacterium gets its own micron-thin shield. Here is how, and why it matters.
View →5Heat stability & shelf lifeStays potent at 30 °C for up to 12 weeks. No fridge needed.
View →6The published researchThree peer-reviewed papers from CSIR and the University of Pretoria, explained.
View →7About VelobioticsThe team turning South African science into probiotics that work.
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