Thomas Heidebach, Petra Forst, and Ulrich Kulozik from the Technical University of Munich report in an up-coming issue of Food Hydrocolloids that rennet could be used to prepare water-insoluble microcapsules based on milk-proteins without significant loss of cells during the encapsulation process.
“This principle could be a suitable alternative to the already established probiotic encapsulation methods, mainly based on ionotrophic gelation of plant polysaccharides like alginate,” they wrote.
“Furthermore the unique functional properties of proteins alleviate the feasibility to control the capsule size of protein-based microcapsules, which is of high importance regarding the sensory impact of microcapsules in final food products,” added Heidebach, Forst, and Kulozik.
As well as providing a technological alternative, there is also the price issue to consider, with alginate price increases in the region of 10-15 per cent still fresh in the mind.
The Munich-based researchers produced water-insoluble, spherical milk protein matrices using rennet (Naturen, Chr. Hansen) with an average size of 68 micrometres.
“For food applications, the average diameter of the added microcapsules is one of the most important characteristics,” they explained. “One aspect is that the capsules must be sufficiently small to avoid a negative sensorial impact on the product
“While firm and irregular shaped particles can already be detected from size ranges of about 10 micrometres in various foods, soft spherical hydrogel microcapsules have a higher threshold for graininess detection.
“It was found that the application of microcapsules in size ranges between 250 micrometres and 1 millimetre caused graininess in yoghurt therefore […] a size below 100 micrometres as desirable to avoid negative sensorial impacts for microcapsules in food,” they added.
For both bacterial strains Lactobacillus paracasei ssp. paracasei F19 (Medipharm AB) and Bifidobacterium lactis Bb12 (Chr. Hansen), a high encapsulation yield was reported.
A test of the viability of the strains after microencapsulation and incubation at pH 2.5 showed that both strains had significantly higher survival that free cells.
“Survival of encapsulated cells can probably be explained by a higher local pH-value within the protein matrix of the capsules caused by the protein buffering capacity, protecting the cells during incubation under simulated gastric conditions at low pH,” wrote the researchers.
“Creating microcapsules from highly concentrated aqueous milk protein solutions enables the formation of microcapsules with a high density gel network, able to offer a favourable micro-milieu for the encapsulated probiotic strains and can therefore be a suitable approach for a more effective application of probiotics in food,” concluded Heidebach, Forst, and Kulozik.
Health and wellness
With the probiotic segment of the market enjoying growth on both sides of the Atlantic, the list of food products that can be used as vehicles for the gut health-boosting bacteria continues to grow.
According to the FAO, probiotics are defined as live microorganisms which when administered in adequate amount confer a health benefit on the host, and this means passing through the gastrointestinal tract alive, and in sufficient numbers.
Microencapsulation has been explored by numerous companies as a way of enhancing gastrointestinal transit of specific strains, and for prolonging the shelf-life of strains in certain foods.
While this new study may support the potential viability of these strains, trials of these strains in humans would be required to confirm if the strains are truly ‘probiotic’.
Source: Food Hydrocolloids Published online ahead of print, doi: 10.1016/j.foodhyd.2009.01.006“Microencapsulation of probiotic cells by means of rennet-gelation of milk proteins” Authors: T. Heidebach, P. Forst, U. Kulozik