The study, being carried out by the UK-based Leatherhead Food, will also reveal how much of the calcium in different products is actually absorbed by the body, and available to offer health benefits.
In the booming functional drink market, mineral- and vitamin-enriched juices and drinks are the largest sector after sport and energy drinks. Calcium is particularly popular as its benefit to bones is well-established, and increasingly recognised as playing a role against osteoporosis prevention and not just for growing children.
But although there are many calcium salts available to product developers, adding calcium to foods creates challenges, particularly at increasing levels of addition.
In many products, the calcium precipitates out of the liquid over time, as demonstrated in past US research on soymilk.
A team at Creighton University in the US has also revealed how different salts offer different levels of bioavailability. In a small study, published in the May issue of the Journal of the American Dietetic Association, they found that women drinking a juice fortified with calcium citrate malate absorbed 48 per cent more calcium than another group drinking a juice with a tricalcium phosphate and calcium lactate combination.
"The info available to manufacturers comes mainly from suppliers who talk about their ingredients," explained Persis Subramaniam, senior food research scientist with Leatherhead, who is coordinating the project.
"The idea is to compare across nine different salts," she said.
The researchers will screen calcium salts, like carbonate, gluconate, lactate, chloride, citrate and phosphates, in the presence of other destabilizing factors like pH, other ingredients such as milk proteins, particle size of the added mineral and processing conditions, she explained.
"Some companies are now trying to produce tea-based drinks with added calcium and the tannins are very sensitive," Subramaniam told NutraIngredients.com.
The researchers will screen salts in model systems, including water, juice, milk and tea and identify ways of stabilizing these systems as the calcium levels are increased.
A second phase will look at bioavailability using an in vitro model based on Caco-2 cells.
"Most studies have been done on a water-based system and are not really related to the drink. There are now more complex drinks on the market and we've been seeing precipiation problems," added Subramaniam.
"Manufacturers know about this issue but they are only now beginning to look at it in real detail."
The project will also investigate functionality of hydrocolloid stabilisers and the effect of particle size on calcium stability. It may include some recently developed nano calcium.