IMAGE-ANALYSIS APPLIED TO ELECTRON-MICROGRAPHS OF STIRRED YOGURT

An optimum or a high heat treatment of milk before yogurt preparation was applied according to an experimental design with the deliberate ai m of making stirred yogurts with varying properties. Images of section s of yogurt samples were obtained using a transmission electron micros cope. These were digitized and segmented via a threshold determination to separate the protein structure from the background. Four spatial s tatistical estimates were determined in order to evaluate their applic ability for characterization of yogurt microstructure. The volume cont ent was estimated and compared with the protein content obtained throu gh chemical analysis. Heat treatment had no significant effect on volu me content, as expected. The surface area of the protein aggregates wa s a useful measure to describe the difference between casein networks obtained by an optimum and a high heat treatment. The star volume gave a measure of the average local size of pores in the yogurt gel. The o ptimum heat treatment resulted in yogurt with small values for the sta r volume, indicating a less coarse structure of the casein network com pared with yogurt prepared from high heat milk. The covariance functio n was able to differentiate between yogurts made using two types of he at treatment.