Scientists from the Department of Chemical Engineering at the University of Birmingham report that fat crystals can form a shell around a liquid oil phase containing water droplets and salt, which would then slowly release salt.
According to findings published in the Journal of Food Engineering, combined crystals of mono- and triglycerides were effective in the stabilisation of the water in oil emulsions, without the need to add other emulsifiers.
The release of salt depends on the temperature, said the researchers. At temperatures above 20 °C – as would be experienced in the mouth – the crystals melt, releasing salt.
“By controlling salt release, it is hypothesised that significant salt reduction can be achieved in processed foods without compromising sensory perception,” wrote the researchers, led by Sarah Frasch-Melnik. “For instance, this could be accomplished by controlling the sodium concentration delivered to the taste buds.
“On the other hand, a significant amount of sodium could be replaced by potassium encapsulated in an inner aqueous phase to hide its bitter by-flavour, thus concentrating sodium in an outer aqueous phase while still lowering the overall sodium content,” they wrote.
“Our work focuses on the release of NaCl through a thin fat crystal shell surrounding a mostly liquid oil phase containing water droplets,” stated Frasch-Melnik and her co-workers.
Salt – a little but not too much
Salt is of course a vital nutrient and is necessary for the body to function, but the average daily salt consumption in the western world, between 10 and 12g, vastly exceeds recommendations from WHO/FAO of 5 grams per day to control blood pressure levels and reduce hypertension prevalence and related health risks in populations.
In countries like the UK, Ireland and the USA, over 80 per cent of salt intake comes from processed food, and people therefore do not realize they are consuming it.
The UK’s Food Standards Agency (FSA) has set targets of 6 grams per day. A recent study from researchers at St. George's University of London appeared to support the clinical relevance of such recommendations.
The study, published in the American Heart Association’s journal Hypertension found that reducing salt intake from 9.7 to 6.5 grams per day reduced average blood pressure from 146/91 to 141/88 mmHg within six weeks.
Frasch-Melnik and her co-workers formulated water-in-oil emulsions stabilised with fat-crystal composed of a mixture of mono- and triglyceride crystals. After one month’s storage at 5 degrees Celsius, only 2 per cent of the salt had been released after one month, but at 30 degrees Celsius, all of the salt had been released after four days, they said.
“It has therefore been shown that salt release in these systems is controlled by temperature, not osmotic pressure gradient,” wrote the researchers.
“It occurs due to imperfections in the shells caused by melting or solvating of crystals as a function of temperature. These imperfections can create a ‘hole’ through which water can leak from the inner to the outer aqueous phase.”
Source: Journal of Food Engineering
Published online ahead of print, doi: 10.1016/j.jfoodeng.2010.01.025
"Fat-crystal stabilised w/o emulsions for controlled salt release"
Authors: S. Frasch-Melnik, I.T. Norton, F. Spyropoulos