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Stability to probiotic cultures and functional foods ingredients

There is accumulating clinical data supporting the role of probiotics in human health particularly in benefiting the immune system, strengthening the mucosal barrier and suppressing intestinal infection. Fermented and unfermented dairy products enriched with probiotic bacteria have developed into one of the most successful categories of functional foods. From a functional ingredient perspective, the generation of these live cultures in dried formats is particularly attractive, however, it does present challenges in terms of retaining probiotic functionality during powder manufacture and storage.

Preservation of probiotics and nutraceuticals by freeze drying presents an effective solution to all of the above challenges. Not only does this method stabilise the product, but it concentrates large quantities down to a very small volume, increasing its potency and producing sizable batches. It also means the end product will not need refrigeration, making it very easy to transport and store.

This method also produces significantly more viable product than other processes, especially when it comes to probiotics. Many more bacteria survive the freeze drying process than with other preservation methods; however they must be protected against the additional stress that freeze drying puts on bacterial cells with a cryo-protectant, such as trehalose, sucrose, glycerol or skimmed milk powder.

Freeze-drying is usually used for sensitive ingredients, as it is employed under vacuum and at low temperatures. However, freeze-drying can cause many negative effects on cells, such as rupture of cell walls, due to water vapor transport to the surface and sublimation of water molecules, protein destruction, and cell shrinkage. It is estimated that the formed crystals in the cooling step cause more adverse effects on cells with a large surface area.

Whilst potentially cheaper and faster preservation methods exist, such as spray drying, vacuum oven drying and fluid bed drying, none can match freeze drying when it comes to maintaining viability of cells. With alternative methods, high temperatures can cause chemical and physical changes to the product, whereas lyophilsation preserves them with low water activity post-lyophilisation; this results in no fundamental changes to the item’s make-up. Freeze-drying is, therefore, the most commonly used form of probiotic dehydration.


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