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New modified starch emulsifier may extend rice bran oil use in food

By Nathan Gray , 10-Jan-2011
Last updated on 10-Jan-2011 at 13:08 GMT

A new modified starch may stabilise rice bran emulsions, says a new study that extends the use of rice bran oil - an ingredient being show “increasing interest” by the food industry.

The research, published in Journal of Food Science, compared the relative performance of whey protein, gum arabic, and a new modified starch at forming and stabilising emulsions of rice bran oil. The new modified starch, which has a higher number of octenyl succinic anhydride (OSA) groups per starch molecule than conventional modified starch, was shown to produce the most stable emulsion.

“This study showed that stable rice bran oil-in-water emulsions can be formed using biopolymer emulsifiers. These emulsions could be used to incorporate rice bran oil into a wide range of food products,” said the researchers, led by senior author Professor David Julian McClements from the University of Massachusetts.

“A novel aspect of this work was that we tested the performance of a newly developed OSA-MS [octenyl succinic anhydride modified starch] as an emulsifier … This study shows that this biopolymer emulsifier can be used at relatively low levels to produce small droplets that have good stability to changes in solution and environmental conditions,” they added.

Rice bran benefits

Rice bran oil is a by-product of milled rice that is used as a cooking and salad oil, due to its high smoke point and desirable flavour profile.

The oil is known to contain a wide range of beneficial compounds including vitamin E complex, phytosterols, and polyphenols. As such, rice bran oil has desirable functional and health benefits, which the authors said merit its use in the production of foods, cosmetics, and pharmaceuticals.

Prof McClements and his co-workers noted that there is “increasing interest” in incorporating rice bran oil into a wide variety of food products. However they said that, in many food applications, oils are present in the form of an emulsion within an aqueous medium, rather than as bulk oils.

“In these systems, it is important that the oil droplets remain both physically and chemically stable throughout the shelf life of the product,” said the authors.

Due to the relatively high levels of functional and nutraceutical components present, the authors said that that rice bran oil may behave differently in emulsions when compared to other edible oils.

McClements and his colleagues said that it is therefore desirable to produce a stable rice bran oil emulsion using biopolymer emulsifiers, which would be able to be incorporated into final products.

As such, the new study investigated the effects of different biopolymer emulsifiers and environmental stresses on the stability of rice bran oil emulsions.

“We selected 3 different surface-active biopolymers that have previously been shown to stabilize oil-in-water emulsions: gum arabic (GA), modified starch (MS), and whey protein isolate (WPI)),” said the authors.

Stable emulsion

At relatively low emulsifier concentrations (emulsifier-to-oil ratio of less than 0.1), the authors reported that whey protein isolate was able to produce smaller droplets during homogenization, than the modified starch of gum arabic.

However, at higher emulsifier concentrations (ratio greater than 1), they observed that the modified starch was able to produce the smallest droplets, when compared to whey protein isolate and gum arabic.

“Emulsions formed using the polysaccharide emulsifiers (modified starch and gum arabic) had much better stability to environmental stresses (pH, salt, and thermal processing) than those formed using the globular protein emulsifier (whey protein isolate),” said McClements and co workers.

They concluded that whilst the whey protein isolate was able to produce small droplets at low concentrations, it had poor stability to environmental stresses. In comparison the new modified starch produced small droplets, and formed an emulsion that was stable to a wide range of environmental stresses.

Source: Journal of Food Science
Published online ahead of print, doi: 0.1111/j.1750-3841.2010.01959.x
“Influence of Biopolymer Emulsifier Type on Formation and Stability of Rice Bran Oil-in-Water Emulsions: Whey Protein, Gum Arabic, and Modified Starch”
Authors: R. Charoen, A. Jangchud, K. Jangchud, T. Harnsilawat, O. Naivikul, D.J. McClements

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