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Enhancing the viability of spray-dried probiotic bacteria by stimulating their stress tolerance
The World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) officially defined probiotics as "live microorganisms which when ingested in adequate amounts confer a health benefit to the host. Although they are generally associated with dairy products, they are found today in a wide variety of human foods and animal feeds. Probiotics are therefore beneficial health bacteria found in various foods and feed products.
However, their manufacture requires production and storage processes that are likely to alter the structural and functional integrity of cells. Freeze-drying, which acts through a combination of cold and vacuum, is the most widely used drying method to preserve bacteria, although it is energy-intensive. Alternatives such as atomisation and fluidisation cost less but they involve the use of hot air, leading to viability and functionality losses.
We designed a simplified and energy-efficient process that maintained bacteria viability close to that of freeze-drying. Unlike the regular process that requires an initial culture stage for the microorganism on an optimum medium (frequently, non-food grade), followed by rinsing and re-suspension in a new medium before dehydration, the new process consists of direct spray-drying of the culture medium. In addition to a gain in productivity, this simplification eliminates risks of contamination at the intermediate stages. Challenged on two probiotic strains, one fragile (Lactobacillus casei) and the other robust (Propionibacterium freudenreichii), this process has demonstrated an efficiency comparable to that of freeze-drying, with respective survival rates of around 40-50% and 100%. The nutrient medium developed utilises whey, a by-product of the cheese-making industry, which is abundant and inexpensive. The dry matter concentration of this medium, in the range of20 to 30% (w/w) dry matter, has been optimised in order to protect bacterial cells during atomisation. Indeed, we showed thathyperconcentrated sweet whey as a culture medium led to bacteria osmoadaptation through the accumulation of compatible solutes (trehalose, polyphosphate), triggering multistress tolerance and enhanced survival upon spray-drying.The stability of microorganisms over time has also been verified at 4 and 6 months, with results comparable to those of freeze-drying.
This innovative process makes it possible to produce dry probiotics in a continuous mode and at 20 to 40 times lower energy costs than freeze-drying, given the lower specific energy consumption of spray-drying and the pre-concentration of the growth medium.This patented process appears to be particularly well suited to producing probiotics for animal feeds. Probiotics could thus offer an alternative to antibiotic therapy and constitute an efficient, ethical, economical and sustainable response to the issues of profitability and animal health.The food sector could also provide the opportunity to mass produce probiotics intended for everyday consumer use.
Huang S, Cauty C, Dolivet A, Le Loir Y, Chen XD, Schuck P, Jan G, Jeantet R.2016. Double use of highly concentrated sweet whey to improve the biomass production and viability of spray-dried probiotic bacteria. J Funct Foods, 23, 455-463 DOI: 10.1016/j.jff.2016.02.050
Huang S, Rabah H, Jardin J, Briard-Bion V, Parayre S, Maillard MB, Le Loir Y, Chen XD, Schuck P, Jeantet R, Jan G.2016. Hyperconcentrated sweet whey, a new culture medium that enhancesPropionibacterium freudenreichiistress tolerance. Applied Env Microbiol, 82, 4641-4651 DOI: 10.1128/AEM.00748-16
Institut National de la Recherche Agronomique, Institut supérieur des Sciences Agronomiques, Agroalimentaires, Horticoles et du Paysage.2015. Method for preparing a probiotic powder using a two-in-one whey-containing nutrient medium. Demande de brevet déposée en Europe le 21 septembre 2015 sous le n° EP 15 306465.4. Inventeurs : Jeantet R, Huang S, Jan G, Schuck P, Le Loir Y, Chen XD.
Science and Technology of Milk and Eggs research unit http://www6.rennes.inra.fr/stlo_eng/
Joint Research Unit INRA and Food and Agricultural Science University (AGROCAMPUS OUEST)
Romain Jeantet - Romain.Jeantet@agrocampus-ouest.fr
Gwénaël Jan - Gwenael.Jan@inra.fr