Most probiotics quietly die between the factory and your medicine cabinet, faster the warmer it gets. A 12-week study at 30 °C shows how the Velobiotics™ micro-shield keeps bifidobacteria alive, and why that matters in a country where the fridge is not always an option.
The short version
- Probiotics were stored as dry powders at 30 °C for 12 weeks, an accelerated test that mimics a hot warehouse, delivery van or bathroom cabinet.
- Unprotected B. longum fell below the therapeutic minimum after 6 weeks and had no live cells left by week 10. Micro-shielded B. longum stayed above the minimum for 10 to 12 weeks.
- Over the full 12 weeks, unprotected B. longum lost 11 log of live cells; shielded cells lost 5 log. That is a million-fold difference in survivors.
- The hardier B. lactis Bb12 benefited too: shelf life at 30 °C went from 5 weeks unprotected to the full 12 weeks shielded.
Probiotics die on the shelf
A live culture is exactly that: alive. From the day it is packed it slowly loses viability, and heat and humidity speed the loss up dramatically. Industry surveys have found that losses of 3 log, a thousand-fold, within 60 days of manufacture are common in dry probiotic products. That is why many brands print "keep refrigerated" and why the count on the label is usually the count on the day of manufacture, not the day you take it.
For most of South Africa, and much of the world, the cold chain is not guaranteed. Products sit in hot delivery vans, un-airconditioned stockrooms and bathroom cabinets. A probiotic that only works out of a fridge is not much use there.
Twelve weeks at 30 °C
Researchers at the University of Pretoria and the CSIR stored micro-shielded and unprotected Bifidobacterium longum Bb46 and Bifidobacterium lactis Bb12 as dry powders in glass vials at 30 °C for 12 weeks, counting live cells every one to two weeks. Thirty degrees was chosen deliberately: it is an accelerated test, hotter than a normal room, so that a year of ordinary shelf life plays out in a few months.
The benchmark was the widely used therapeutic minimum of 10⁶ live cells per gram (6 log). Below that, a probiotic is generally considered to have too few live cells to be effective.
Weeks more life, a million times more cells
B. longum Bb46 is the more delicate of the two species, and it showed the biggest benefit. Unprotected cells dropped below the therapeutic minimum after six weeks and were completely gone by week ten. Shielded cells stayed above the minimum for ten weeks (production sample) to twelve weeks (reactor sample). Over the whole period, unprotected cells lost 11 log of viability; shielded cells lost 5 log. Put differently, after 12 weeks of heat there were about a million times more live shielded bacteria than unprotected ones.
B. lactis Bb12 is naturally hardier, and it still benefited: unprotected cells fell below the minimum at week five, while shielded cells stayed above it for the full twelve weeks. The final difference was 3.3 log, about two thousand times more live cells.
Keeping the water out
Water is the enemy of a dormant bacterium. A little humidity wakes it up; awake, it consumes what little food it has and dies. The Velobiotics™ shield is a hydrogen-bonded mesh of two polymers that holds noticeably less water than the same polymers loosely mixed, about 30% less in the CSIR's humidity tests. Throughout the 12-week study the water activity of the powders stayed between 0.25 and 0.43, and the periods of highest water activity coincided with the biggest losses in every sample, shielded or not. The shield does not make the bacteria immortal; it slows the clock dramatically.
“This method of encapsulation reveals the possibility for manufacture of encapsulated probiotic powders with increased stability at ambient temperatures. This would potentially allow the supply of a stable probiotic formulation to impoverished communities without proper storage facilities.”
— Thantsha, Labuschagne & Mamvura, World Journal of Microbiology and Biotechnology, 2014
The science in detail
Storage conditions, water activity, species differences and the full numbers.
Storage conditions and measurement
Samples were stored as free powders in glass vials at 30 ± 2 °C for 12 weeks. Sub-samples were taken every 7 or 14 days for water activity (aw) and viable counts, plated in triplicate on MRS agar with 0.05% cysteine hydrochloride and incubated anaerobically. Water activities across all samples ranged 0.25–0.43 (mean 0.34). Each reported value is the mean of triplicate counts from three independent experiments.
Full results by species
B. longum Bb46. Unprotected: −6 log after 8 weeks, no viable cells at 10 weeks, above 6 log CFU/g only until week 6, total reduction 11 log at 12 weeks. Shielded (product chamber): above 6 log for 10 weeks, −4 log at 8 weeks, total reduction 5 log. Shielded (reactor-harvested): above 6 log for 12 weeks, −3 log at 8 weeks. Reactor samples were significantly higher than unprotected (p < 0.05); product-chamber samples somewhat higher (p = 0.05).
B. lactis Bb12. Shielded cells lost 5 log over 12 weeks; unprotected cells dry-mixed with unprocessed and processed polymers lost 6 and 8 log respectively (−8.2 log at the end point vs −4.9 log shielded). Unprotected samples fell below 6 log CFU/g by week 5; shielded stayed above 6 log to week 12. The largest losses for every sample occurred in weeks 3–5, coinciding with the highest water activities.
How this compares with other encapsulation methods
The authors compared their results with published alginate, gelatin and protein-carbohydrate encapsulation studies, which typically report survival gains of 0.5 to 2 log over 2 to 12 weeks, mostly under refrigeration. The 6-log gain for B. longum at 30 °C is among the largest reported. The authors also noted that shear and heat during atomisation slightly reduced viability compared with reactor-harvested material, and that the product-chamber material was used for further work because it reflects practical large-scale production.
References
- Thantsha MS, Labuschagne PW, Mamvura CI. Supercritical CO₂ interpolymer complex encapsulation improves heat stability of probiotic bifidobacteria. World Journal of Microbiology and Biotechnology 2014;30:479–486. PDF
- Moolman FS et al. Encapsulating probiotics with an interpolymer complex in supercritical carbon dioxide. South African Journal of Science 2006;102:349–354 (moisture absorption data). PDF
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 →4Surviving stomach acidPeer-reviewed: 40 to 65 times more live bacteria make it through.
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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