Researchers from the University of Massachusetts and the Università di Bologna compared the efficacy of whey protein isolate (WPI) and gum arabic (GA), commonly used to stabilise citrus oil emulsions in foods and beverages, and found that whey protein performed better for protecting the flavour ingredient against deterioration.
"Emulsions stabilized by WPI had a better creaming stability than those stabilized by GA because the protein emulsifier was able to produce smaller lipid droplets during homogenization," wrote lead author Darinka Djordjevic in the journal Food Chemistry.
"These data suggest that WPI was able to inhibit the oxidative deterioration of citral in oil-in-water emulsions."
The use of citrus oils for flavouring food and beverages is common, with citral (3,7-dimethyl-2,6-octadienal) regarded as one of the most important of these. However, the compound is susceptible to degradation from acid and oxygen
"Consumer demand for natural flavour ingredients and more complex and authentic aroma profiles have resulted in an increased demand for the incorporation of citrus oil and citral, into different food and beverage products," explained Djordjevic.
"However, incorporation of chemically unstable citrus oil components into foods and beverages presents a challenge for the food industry because their chemical deterioration needs to be inhibited to minimize loss of product quality."
The new study looked at the ability of gun arabic or whey protein isolate to stabilise emulsions at pH 3.0 (acidic conditions) and pH 7.0 (neutral). The degradation of citral was measured using the formation of the oxidation product p-cymene as a marker, and the researchers report that for both pH levels, p-cymene levels were less in the WPI-stabilised emulsions.
This beneficial effect was proposed to be due to the whey protein forming droplets that were able to repel oxidising metals in the emulsion.
The whey protein isolate also produced a more stable cream, said the researchers.
"Emulsions stabilized by WPI had a better creaming stability than those stabilised by GA because the protein emulsifier was able to produce smaller lipid droplets during homogenisation," wrote the researchers.
The study highlights the potential of whey protein to improve flavour retention in beverages and foods, with further research needed to test the potential of the protein in other formulations and in the presence of other ingredients.
Whey protein is increasingly hitting the mainstream. It is now on supermarket shelves, and is used extensively in infant formula.
Whey has long been used for its functional properties, but it is also now being added because of nutritional properties. It is natural, has no E-numbers and can be used by food makers to reformulate their products to take out additives.
A recent survey by Danish 3A Business Consulting on whey and lactose ingredients, suggested that food makers are increasingly viewing whey and lactose products as an ideal means of achieving added value. As such the global whey protein concentrates and isolates market is estimated at 395,000 MT in 2004 representing a value of just over $1bn.
The US remains the biggest producer at 187,000 MT followed by Europe with 159,000.
Source: Food Chemistry (Elsevier)
15 January 2008,Volume 106, Issue 2, Pages 698-705
"Stability of citral in protein- and gum arabic-stabilized oil-in-water emulsions"
Authors: D. Djordjevic, L. Cercaci, J. Alamed, D.J. McClements and E.A. Decker