"Our group is currently exploring approaches to tackle this challenging area [of producing thermoresistant probiotic microorganisms] and is focusing on developing novel encapsulation systems," wrote authors Anil Kumar Anal and Harjinder Singh in the journal Trends in Food Science & Technology.
Most foods containing probiotics, bacteria found in the gut that are understood to have health benefits, are found in the refrigerated section of supermarkets, as the bacteria are destroyed by heat and other processing conditions.
This has given the dairy sector, already used to handling live bacteria for the manufacture of yoghurt, a major advantage in probiotic foods. Probiotic drinking yoghurts are currently the fastest growing dairy product in Europe.
But research has increasingly focused on expanding protecting probiotics during processing and increasing the number of food categories currently available to prebiotics.
"[Our approaches are] based on an understanding of the thermal conductivity properties of several food-grade biopolymers and lipids that are used as encapsulating shell materials, individually and in combination. These microencapsulation systems may also control the diffusion of oxygen across the wall and may ensure a smaller log reduction in the viability of cells in foods," wrote the scientists from the Riddet Centre at New Zealand's Massey University.
"Coating of capsules with some lipids, with high melting points, may also provide low moisture conditions and an anaerobic environment for probiotic bacteria and may possibly improve thermal stability."
Anal and Singh reviewed various hydrocolloids that could have potential as probiotic encapsulators. These included alginate, chitosan, carboxymethyl cellulose (CMC), carrageenan, gelatin and pectin.
These ingredients are applied using the spray- and freeze-drying techniques. The reviewers note that while such techniques may yield large quantities of material, the encapsulated bacteria are not well protected from temperature and extremes of external water concentration.
This is opening up opportunities for ingredients such as trehalose, which could be used to improve survival, they said.
"In a recent study, freeze-dried Lactobacillus bulgaricus survived better during storage at minus 20 degrees Celsius over 10 months when cells had been grown in the presence of fructose, lactose or mannose or when glucose, fructose, monosodium glutamate or sorbitol was added to the drying medium," wrote Anal and Singh.
"In particular, trehalose, a disaccharide of glucose, has been found to be effective at protecting the bacterial cells during freezing and drying," they added.
In the review of the science behind probiotic encapsulation, Anal and Singh tap into the trend of finding encapsulation methods for the friendly bugs. Indeed, Leatherhead Food recently launched a collaborative industry study to assess microencapsulation systems for preserving probiotic bacteria and boosting their effectiveness in the gut.
In collaboration with the University of Reading, Leatherhead is giving industry players the opportunity to come in on a collaborative research effort that could provide them with the know how to differentiate their products in an increasingly crowded marketplace.
Source: Trends in Food Science & Technology (Elsevier) May 2007, Volume 18, Issue 5, Pages 240-251
"Recent advances in microencapsulation of probiotics for industrial applications and targeted delivery"
Authors: A.K. Anal and H. Singh