X rays tell stirring tale about fat

From Indianapolis, at the March meeting of the American Physical Society

In a novel example of physics probing beneath the veneer of everyday phenomena, scientists have used X rays to look at the microstructural details of fats as they’re mixed and cooled during food manufacturing.

The size, shape, and stability of fat crystals in foods affect such qualities as margarine’s spreadability and ice cream’s feel in an eater’s mouth, says Gianfranco Mazzanti of the University of Guelph in Ontario. Chocolate makers seed their products with fat crystals of certain structures to encourage batches to come out with consistent properties.

In new experiments, Mazzanti, Alejandro G. Marangoni of Guelph, and Stefan Idziak of the University of Waterloo in Ontario mimicked conditions in food-processing plants. There, the blades of powerful mixing machines subject food ingredients, including fats, to intense shear forces, which tear the substances.

Food scientists hadn’t previously investigated the dynamic response of fat microstructure to such processing, Mazzanti says.

To produce industrial-strength shearing in a small laboratory apparatus, the researchers poured milk fat into a gap only millimeters wide between two concentric cylinders about the size of Italian espresso cups. Then, they spun the inner metal cylinder at speeds of up to 1,000 revolutions per minute.

Using X rays generated by a synchrotron at Brookhaven National Laboratory in Upton, N.Y., the team recorded diffraction patterns as the fat underwent shearing and solidified into crystals at varying cooling rates.

Preliminary analysis of the X-ray data indicates that strong shear and rapid cooling can lead to crystals that are initially only nanometers across but quickly swell to tens of micrometers. The larger crystals appear to be shaped like plates.

Marangoni says the team may have glimpsed a type of seed crystal that the motions of food processing just happen to produce. Learning how such seed crystals form may lead to means of controlling their structure and, ultimately, those tangible properties that diners notice (SN: 5/7/94, p. 296), he adds.