Microcapsules for functional food: A milk protein wrapper protects probiotic microbes
Food products should be tasty and filling – but healthy, too. In an attempt to give nature a helping hand, products are increasingly being enriched with vitamins, plant extracts or probiotics. Unfortunately, the health benefits of these organisms are often disputed since they do not always reach their intended destination, the gut, alive and intact. Acids contained in food products destroy many of the healthy bacteria during storage, and upon ingestion the surviving microbes are further set upon by gastric acid. Researchers at the Weihenstephan Research Centre have now developed a novel microencapsulation technology to improve the deployment of probiotics in functional foods.
To date these useful bacteria were frozen or dried before being added to yoghurt in a highly concentrated powder form. Yet even before the expiration date the number of active probiotic microbes in packaged products is often strongly reduced. The solution: wrap the microbes in a protective shell. So-called microcapsules allow the enclosed substances to be released in a controlled manner. Encapsulation is already well established for medication and crop protection agents, with applications in the food industry being researched intensively. After all, microcapsules for human consumption must fulfil very special demands. They must be taste-neutral and suitable for daily ingestion, and at the same time be small and smooth enough to go “undetected” by the tongue.
Prof. Ulrich Kulozik and his assistant Thomas Heidenbach from the Technology Department of the Nutrition and Food Research Center (ZIEL) at the Weihenstephan Research Center, have developed food-compatible microcapsules that fit the order. In a large-scale, publicly funded research project they discovered not only a fitting wrapper substance, but also a suitable production process. Employing enzymes as natural biocatalysts, the researchers pack probiotics into the capsule material, thereby shielding them from deterioration through gastric acid.
The food scientists chose the milk protein casein because it blends well with many substances and is also taste compatible with dairy products. Furthermore, there are no consumer acceptance problems when this natural product is used in yoghurt and whey drinks. The researchers use food chemistry to transform the casein into functional microcapsules. The probiotic microbes are first combined with milk protein, which serves as the wrapper material. When the enzyme transglutaminase is added to this mixture a water-in-oil emulsion results, leading to the formation of a casein gel that encloses the healthy bacteria in a tightly sealed wrapper (see figure).
The tiny capsules, measuring on average only 150 microns across, are then separated in a centrifuge and washed. One gram of microcapsules contains some five million microbes. Neither the storage during the normal product shelf life nor gastric acid can harm the filled protein capsules. Only upon contact with enzymes in the small intestine do the microcapsules release their valuable payload, precisely there where they are needed. This novel process is now being developed to market maturity in close collaboration with the food industry.
The economic significance of microencapsulation in the food industry has grown continuously in recent years. Between 1996 and 2004 probiotic dairy products saw a six-fold growth in sales to 485 million euros. In the future, enrichment with probiotics will not be limited to dairy products. Cereals, sausage products, ready–to-eat food products and all kinds of dietary supplements will follow – calling for a variety of novel encapsulation systems.
By making their developments available to all producers without restriction, the Weihenstephan researchers are making an important contribution to the promotion of small and mid-sized companies that generally do not support research facilities of their own.
Prof. Dr.-Ing. Ulrich Kulozik
Dipl.-Ing. Thomas Heidebach
Chair for Food Process Engineering and Dairy Technology
Technische Universität München
Tel: 08161 / 71 – 5317