THE SURFACE COVERAGE OF FAT ON FOOD POWDERS ANALYZED BY ESCA (ELECTRON-SPECTROSCOPY FOR CHEMICAL-ANALYSIS)

ESCA (electron spectroscopy for chemical analysis) was used to estimate the fat coverage on different spray-dried food powder surfaces. The method presented here represents a new way of estimating the actual surface coverage of fat on a food powder. The ESCA-method is illustrated with three different series of experiments. The results obtained with the ESCA-technique are combined with the results obtained from the conventional free fat extraction technique for different spray-dried powders. In the first series, emulsions containing different ratios of protein to fat were spray-dried. An increase in the amount of fat in the emulsion gives an increased surface coverage of fat. Powders with a high fat content shows a high free fat level, indicating a continuous network of fat inside the particles. Secondly, the effect of heat treatment on the ability of bovine serum albumin to encapsulate fat has been investigated. The results show that albumin treated at high temperature encapsulates the fat less completely than the albumin treated at low temperature. Finally, emulsions containing oil phases with different melting points were spray-dried and analyzed. Powders with a high melting fat show very well encapsulated fat with only a minor surface coverage of fat. Powders with a qualitatively different distribution of fat can be identified by comparing the surface coverage of fat estimated by ESCA with the free fat measurements.