From metal bars to candy bars; materials scientists turn to what you're eating and how you eat it

Science News, Feb 17, 2001 by Jessica Gorman

A series of pictures taken by the team shows the gradual development of an emulsion--a structure that can imitate fat when used in low-fat products such as spreadable margarine substitutes. Hermansson says that such images could enable food scientists to predict what microstructures, and thus textures, will form when they mix and process various ingredients.

Polymer physicist Richard Jones of the University of Sheffield in England works with similar mixtures. The goal for a low-fat spread, dessert, or salad dressing is to close the fat but retain the creamy feeling, he says. Since the natural texture of whipped cream, for example, comes from networks of fat molecules, Jones--like Hermansson--tries to reproduce that structure with nonfat ingredients, such as water-soluble starch and gelatin that mimic the role of fat molecules. With the right temperatures and other processing conditions, the ingredients can form an interconnected network resembling the texture of natural fat in foods, he says.

Research has shown that different processing conditions can create different textures and mechanical properties, Jones notes. For example, a food researcher might want to create a continuous gelatin network that's stable in a starch solution, he says. Or, for a smoother texture, the processing temperature could be changed to permit the gelatin to break up into small droplets.

In recent work, Jones' team has found processing conditions that create something resembling a foam. The walls of the foamy structure contain the gelatin, he says, and each cell of the foam fills with a nongel solution, such as starch. Jones is particularly interested in the interface where the gelatin meets the nongelatin solution. Analyzing it will help him understand the mechanical properties of the material, he says, such as "whether it spreads like butter, the way it breaks, and the kind of texture it has."

Food scientists are helping to design low-fat foods, but what about the ones we often feel compelled to eat despite their load of fatty molecules?

Here, the analogy with metallurgy is especially strong. Much like a metal alloy, a chocolate treat must undergo careful shepherding through complicated processing to achieve a desirable structure.

Cocoa butter, the yellow-white fat made from cacao beans, comes in several different crystal forms. Only one of these structures produces tempting, glossy, melt-in-your-mouth chocolate. Creating that structure requires a procedure called tempering--a series of steps with controlled heating, cooling, and mixing.

The other crystal forms don't give consumers either the look or the taste that they demand in chocolate. For example, chocolate left on a kitchen shelf for several months morphs into a different crystal form, one with a familiar white film called fat bloom. This chocolate can taste gritty because some of its crystals don't melt at the temperature inside a person's mouth, notes chemical engineer Peter Fryer of the University of Birmingham in England. His work is sponsored in part by the chocolate company Cadbury, also in Birmingham.