The quest to reduce saturated fats

The most common way to provide texture to oily food products is by having a network of small crystallites of triglycerides (also known as crystalline triglyceride hardstock) present, which is rich in saturated fatty acids. Saturated fat raises blood cholesterol and it is present, among others, in dairy products, chocolate, fatty meat and some prepared foods.

To find healthier alternatives to the crystalline triglyceride fat, scientists are looking for structurants that do not raise blood cholesterol. Researchers at Unilever discovered serendipitously that the mixture of γ-oryzanol with β-sitosterol could be used for this purpose. These materials belong to the class of plant sterol(ester)s that are actually known to reduce blood cholesterol, and β-sitosterol-esters are added to some margarines, such as Flora pro activ, for this specific purpose. In many aspects, the mixture behaves differently from a normal crystalline particle network and it is more reminiscent of so-called organogels, which raised questions concerning the supermolecular structures in these systems. “The ESRF covers all of the length scales involved in the structuring of this mixture, so our results encouraged us to pay a visit to the ESRF,” explains Ruud den Adel, research scientist at Unilever.

The team used small-angle and wide-angle X-ray scattering at the high-brilliance beamline ID2 and also carried out some complementary X-ray diffraction measurements at the Unilever labs. They found that the mixture of γ-oryzanol with β-sitosterol creates a network of tubules in edible oil (sunflower oil in this particular study) that form rapidly when cooled below the melting point of the gel. Potentially, tubules structure a network very effectively because the surface-to-volume ratio is high. The tubules have a diameter between 6.7 and 8 nm, and a wall thickness of 0.8 to 1.2 nm. The thin tubules do not scatter much light, and therefore a block of “structured“ oil is almost transparent, which is not the case for regular fat.

Because most foods contain water, the researchers also considered the effect of the presence of water on the structuring capability of the mixture of γ-oryzanol with β-sitosterol in emulsions. It was found that water interferes with hydrogen bond formation between γ-oryzanol and β-sitosterol, which is responsible for the formation of the tubules in oil. Tubule formation can be retained by controlling the water activity in the emulsion. “To exploit this effect in foods remains a challenge because product developers tend to have limited formulation freedom when designing a recipe,” explains den Adel.

References
A Bot et al. 2009 Food Biophysics 4 266–272.
A Bot et al. 2011 Food Hydrocolloids 25 doi:10.1016/j.foodhyd.2010.07.026.
M Pernetti et al. 2007 Current Opinion in Colloid & Interface Science 12 221–231.

M Capellas

This article appeared in ESRFnews, December 2010. 

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Top image: Margarine and butter normally contain saturated fatty acids, which lead to an increase in blood cholesterol and a higher risk of heart disease. (Credit: istockphoto/Suzanne Tucker).