Yeast as friend and foe in food production. From SOFHT Focus 25 Autumn 1998
The most familiar uses for yeast are for brewing and baking, but these microscopic organisms can be used for more unusual applications for flavouring additives and for food forensic analysis
Scan the contents of any manufactured food product and one ingredient appears almost every time - flavouring. Lemon, lime, orange, mint, onion, garlic, chocolate and a multitude of other tastes are incorporated into food with flavouring additives. Unlike their source material, these additives are dry, easy-to-handle and ready-to-use.
However, such additives can be expensive to produce. The flavour is held in microscopic capsules made either of food-approved polymers, or proteins such as gelatin. The liquid flavour is added to the capsule by spray drying, a heat intensive, and therefore costly process. In many instances, the flavouring may be the most expensive ingredient in the food.
Now the British Textiles Technology Group (BTTG) has developed a biotechnology-based capsule, which absorbs flavours and can be loaded up to 70 per cent by weight. This compares with the maximum 40 per cent that can be achieved with spray drying. Adding to the appeal of this development, the capsules are made from what is otherwise a waste material - spent yeast from the brewing industry. "Yeast cells are naturally preformed capsules, and it turns out that if you mix a flavouring with spent yeast, the flavouring enters the empty yeast cells by osmosis, a process that requires no additional energy source," says Dr Gordon Nelson of BTTG. Not only is the yeast microcapsule cheaper to produce, the flavouring is more intense, meaning that less is required for the same effect. "Once the yeast membrane comes into contact with the tongue all the flavour is released directly onto the taste buds," says Dr Nelson.
By contrast, with protein or polymer capsules, the membrane has to be chemically broken down by saliva, and some of the flavouring material is swallowed before this happens. Dr Nelson estimates that by using yeast encapsulated flavours, many manufacturers could cut levels of flavour additives to between one fifth to one tenth of the amount currently used and still get the same flavour intensity.
The yeast capsules can be loaded with a wide range of flavours and they can be used in a variety of food products including confectionery, soft drinks, crisps and savouries."Some products which normally would not be able to hold flavours, now have the potential to incorporate them. For example, it is difficult to get lipid (oil) based flavours into low fat products such as yoghurts, as these contain a high percentage of water. The yeast is hydrophilic (water-loving) and will remain in suspension," says Dr Nelson. BTTG took out patents on the yeast encapsulation process and has been working to commercialise the technology. There are a number of trials under way and the first products using these flavourings should be available within the next year. The process of encapsulating the flavour is easy to scale-up. "You just need a commercial mixing vessel," says Dr Nelson.
While yeast is poised to provide an improved method of flavouring food, it can also be a nuisance to some food processors. Many products contain yeast, either as an ingredient or as a contaminant. Problems can occur because yeast’s cause sugars to ferment. This not only spoils products, giving them an "off" alcoholic taste, but can also be dangerous, as the fermentation generates carbon dioxide, causing cans and bottles to explode.
Professor Robert Davenport, a consultant to the food industry, has developed a system of 'yeast forensics' which enables food and drink companies to track down causes and sources of yeast contamination. The tests can be predictive - indicating what type of yeast is likely to contaminate a particular product, bearing in mind the raw materials and the processing conditions. They can also be used to predict possible consequences of yeast contamination, allowing companies to make decisions on how long ingredients can be stored for, and appropriate processing times and temperatures.
An example of the application of yeast forensics was at a cider production plant, which had a problem of low level but consistent spoilage. The company had identified the likely cause as a malfunction in the filtration process in which spent yeast was filtered out of the cider. Using a marker yeast, Metchnikowia pulcherrima (this yeast was chosen as it produces brilliant purple sheen growth colonies, which helped to trace the yeast as it progresses through the production process) the problem was tracked down to a fault in the filtration sheets.
In another case concerning the manufacture of a health drink, it was found that the organism causing the contamination had become resistant to the preservative used in the product and actually required it for growth. This allowed the contaminating yeast to grow in the health drink. This case was complex with product formulation, hygiene controls and manufacturing practice all contributing to the problem. The health drink showed spoilage symptoms due to contamination with the yeast Zygosaccharomyces bailii. This was an exceptional strain of yeast, able to synthesise all of its essential B group vitamin requirement, thus allowing residual amounts of ammonia (from 'cheap' caramel colour) to be used as a nitrogen source. Also, the factory environment had allowed the strain to develop and become resistant to the benzoic acid preservative used in the health drink. The forensic work carried out by Professor Davenport led to changes in product formulation and hygiene controls in the factory. While most people think of yeasts as an ingredient in bread and drinks, yeast contamination can affect a range of products. Other foods where Professor Davenport's yeast forensics has sleuthed out this culprit include pickles/sauces, salad creams, confectionery, bakery products and frozen peas.
This case study was supplied courtesy of the BMB Initiative whose helpline is: 0800 432 100.
Picture of yeast courtesy of Gist-brocades UK, the bakery innovators. Gist-brocades have a master collection of Baker's Yeast, containing over 4,000 different yeast strains.
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