Developing methods to make fermented food healthier

Hani El Kadri, a PhD student with the School of Chemical Engineering, has produced research that could help to revolutionise the food industry. His work, recently published in an international journal, paves the way to significantly improve the way bacteria can be used for advancing the processing of fermented foods and for the delivery of beneficial bacteria to our gut.

The ‘double emulsion’ formulation method, which can also be used to maintain food flavour when removing fat content, has been developed in a new way to make ‘good’ food even better.

Hani’s research is the subject of a paper he has written with colleagues Dr Tim Overton and Professor Serafim Bakalis, as well as his supervisor, Dr Kostas Gkatzionis, from the School of Chemical Engineering. Entitled ‘Understanding and controlling the release mechanism of Escherichia coli in double W1/O/W2 emulsion globules in the presence of NaCl in the W2 phase’, it was published in RSC Advances and has won the College’s Paper of the Month award.

‘There’s a huge discussion about the benefits of bacteria in our diet,’ says Kostas, a Lecturer in Microbiology. ‘We’re talking here about real food – and making real food even better food, using technology to deliver beneficial or “good” bacteria. We should be eating more bacteria and bacterial fermentates – products that bacteria produce during metabolism in food fermentation – anyway, and so what we’re doing is trying to help the industry, to improve food fermentation by standardising, or controlling, the delivery of bacteria.’

Many foods are structured solids, whose microstructure determines their taste and texture. A major component of a lot of formulated foods is an emulsion phase.

Double emulsions are discrete liquid dispersions in which droplets of the dispersed phase contain smaller water droplets of similar – but not necessarily identical –composition as the continuous phase. In other words, they are an emulsion within an emulsion. For example, you could have water that contains droplets of oil, but with the droplets of oil having droplets of water in them.

‘So the oil phase is separating the two water phases, which is a method that has been developed to reduce the fat content of food – by replacing oil with water – without compromising the taste,’ explains Kostas.

What he and Hani are working on is the biological applications of this ‘double emulsion’ method. So in the inner phase, bacteria are added within the water.

‘This system potentially can be used for encapsulating beneficial bacteria such as the kind we get from the likes of yoghurt and cheese. There are many other beneficial bacteria – probiotics – we can add, too.’

For their research, Hani and Kostas used E.coli as a model organism. Although E.coli is not in itself beneficial and some of its variants are associated with diseases, certain strains are used as models in microbiological research.

The reason double emulsions are so important is that the bacteria are protected inside the droplets.

‘Gastric juice isn’t very friendly to bacteria, so by delivering probiotics this way, they won’t die until they get to where they need to go, which is the intestine,’ explains Hani.

This system also enables the processing of fermented foods, which include cheese, milk and meats, to be achieved more efficiently.

‘Sometimes the bacteria you need for processing the food is different from the bacteria you need to benefit your gut,’ says Kostas. ‘So you can use the system to have a starter culture (in the outer water phase), with one species of bacteria, and a secondary culture or flora (in the inner water phase), with another species – both designed to achieve different things.’

What makes Birmingham’s research unique is that Hani, Kostas and their colleagues have shown that it is possible to release bacteria from the inner water phase of the droplets in a controlled manner and, for the first time, to be able to observe and describe the mechanism.

‘By encapsulating microorganisms inside droplets, we improve the quality of what is delivered, and we deliver them at the right time, rather than relying on the environment.’

The key, then, is how this release is achieved.

‘What Hani has done – and what the paper is about – is to study how to release the bacteria by altering the osmotic balance using sodium chloride (salt). If you have a stable double emulsion system, you should have an osmotically balanced structure. Once you alter that, it becomes unstable, so water can go in or out – drawn to a higher concentration. What we’ve done is to look at how the bacteria are participating as part of this mechanism.’

Their research has found there is some diffusion of water, but it is only when it gets to a critical point does the emulsion collapse and the bacteria burst out. ‘The bacteria do not follow the water leakage between the inner and outer phases of the droplets, but they are released when the droplets collapse and burst.

‘What our study discovered what was by changing the structure of the double emulsion, we could control the release through the bursting of the droplets, and that the bursting mechanism can be controlled by changing the composition of the emulsion. We could also use this understanding to make an emulsion more stable – to delay bursting – if, say, a foodstuff needed two months of ripening.’

Research is still at an early stage, but its potential for real-world application is huge.

‘It’s a stepping stone,’ says Hani, modestly. ‘A lot of work still needs to be done in terms of the fermentation process, but it’s a very good start to understand how to control the release of bacteria. There are many, many species of bacteria offered by the food industry and now they can be used in a better way through the double emulsion process.’