Moisture sorption phenomena of lactose anomers and evaluation of morphological stability.

The importance of knowing the phenomenon of moisture sorption and the microstructural evolution in lactose anomers, lies in being able to establish its applicability. Thus, the moisture sorption phenomenon of four types of lactose anomers (C-βL, S-βL, F-αL and C-αL∙H2O) was studied, constructing adsorption isotherms at three storage temperatures (15, 25 and 35 °C), and fitting the experimental data with four mathematical models (BET, GAB, Peleg and Caurie). The analysis of the adsorption isotherm data, showed that: (i) β-lactose anomers adsorb less moisture than α-lactose anomers. (ii) In β-lactose anomers, purity influences stability, keeping a broad range of water activities. (iii) Increasing the storage temperature reduces the water activity range in which the anomers are stable. (iv) Based on the R2 parameter at 15°C the best fit was achieved by employing the GAB model for the four lactose isomers, Specifically, the R2 values were as follows: C-βL=0.993, S-βL=0.996, F-αL=0.905, and C-αL∙H2O=0.98. The morphological evolution of lactose particles studied by scanning electron microscopy (SEM) showed particles of irregular morphology in the α-lactose anomers. Commercial β-lactose anomer presented particles with irregular morphology and few with curved morphology, suggesting the presence α-lactose as contamination. The synthesized β-lactose anomer presented mostly curved particles, indicating its high purity. In β-lactose anomers, mutarotation into α-lactose was observed with increasing storage temperature.