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Formation and Growth Phenomena of Lactose Nuclei Under Contact Nucleation Conditions

Department of Food Science, University of Wisconsin, Madison 53706

ABSTRACT

Contact nucleation of -lactose was studied in a photomicroscopic cell by gently sliding a parent crystal against a cover glass at different temperatures (303 to 333° K) and relative supersaturations (.6 to 2.8). It was observed that the growth rate dispersion phenomenon existed in the lactose system and followed the constant crystal growth model. Both gamma and normal distributions fit the growth rate dispersion of lactose nuclei well. The variance of the growth rate distribution increased as temperature and supersaturation (hence, mean growth rate) increased, and their relationships were modeled in this study. The average growth kinetics of these contact nuclei of lactose were approximately second order in supersaturation with an activation energy of 9.8 kcal/mol.

A range of supersaturations was observed in which contact nuclei were formed but the nuclei were unable to grow. That is, the critical supersaturation for growth was higher than that for formation of these lactose crystals. This observation may be the result of mass transfer limitations to growth in the photomicroscopic cell.