Food Structure


B. E. Brooker


The interfacial structure of air bubbles in normal and defective whipped creams were compared, using freeze fracturing and transmission electron microscopy , in an attempt to understand the underlying mechanism of t he observed gross differences in their whipping times and overruns . In normal whipped creams sparsely distributed fat crystals were found to have penetrated some of the bubbles and were lying in the plane of the air/water interface.

In defective whipped creams , large numbers of needle-like crystals had penetrated the air/water interface of every bubble and, as a consequence, reduced numbers of fat globules were found to have adsorbed . There was also morphological evidence that the crystals reached the interface before the milk fat globules during the whipping process . The presence of large masses of free fat in the aqueous phase of whipped cream, on whose surface arrays of very long fat crystals were found, suggested that the needle-like crystals were dislodged by the shear forces generated during whipping and were then free to adsorb to bubbles . The detection of such large amounts of free fat indicated a large scale damage to fat globules during processing with the consequent escape of both crystalline and liquid fat.

Possible mechanisms to account for the low overrun and long whipping times in defective creams are discussed.

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