Selective anomer crystallization from aqueous solution: Monitoring lactose recovery under mutarotation limitation via attenuated total reflection Fourier-transform spectroscopy and theoretical rate analysis.

Lactose is typically produced via cooling crystallization either from whey or whey permeate (edible grade) or from aqueous solution (pharmaceutical grade). While in solution, lactose is present in 2 anomeric forms, α- and ß-lactose. During cooling crystallization under standard process conditions, only α-lactose crystallizes, depleting the solution of α-anomer. In practice, mutarotation kinetics are often assumed to be much faster than crystallization. However, some literature reports limitation of crystallization by mutarotation. In the present research, we investigate the influence of operating conditions on mutarotation in lactose crystallization and explore the existence of an operation regimen where mutarotation can be disregarded in the crystallization process. Therefore, we study crystallization from aqueous lactose solutions by inline monitoring of concentrations of α- and ß-lactose via attenuated total reflection Fourier-transform spectroscopy. By implementing a linear cooling profile of 9 K/h to a minimum temperature of 10°C, we measured a remarkable increase in ß/α ratio, reaching a maximum of 2.19. This ratio exceeds the equilibrium level by 36%. However, when the same cooling profile was applied to a minimum temperature of 25°C, the deviation was significantly lower, with a maximum ß/α ratio of 1.72, representing only an 8% deviation from equilibrium. We also performed a theoretical assessment of the influence of process parameters on crystallization kinetics. We conclude that mutarotation needs to be taken into consideration for efficient crystallization control if the crystal surface area and supersaturation are sufficiently high.

Interferometric Probing of Physical and Chemical Properties of Solutions: Noncontact Investigation of Liquids.

Interferometry is a highly versatile tool for probing physical and chemical phenomena. In addition to the benefit of noncontact investigations, even spatially resolved information can be obtained by choosing a suitable setup. This review presents the evolution of the various setups that have evolved since the first interferometers were developed in the mid-nineteenth century and highlights the benefits, limitations, and typical areas of application. This review focuses on interferometry based on electromagnetic waves in the near-infrared and visible range applied to liquid samples, categorizes the chemical/physical properties (e.g., pressure, temperature, composition) and phenomena (e.g., evaporation, crystal growth, diffusion, thermophoresis) that can be assessed, and presents a comprehensive literature review of specific existing applications. Finally, it discusses some fundamental open questions with respect to geometric considerations and overlapping effects.

Pressure-induced phase transitions in triacylglycerides.

The melting point of triacylglycerides (TAGs) under atmospheric pressure depends on both the fatty acid composition and crystalline structure of the polymorphic state, which are influenced by the temperature treatment history of the TAG. In this contribution, the additional effect of high hydrostatic pressure is described. Samples were placed in a temperature-controlled cell and pressurized up to 450 MPa. The phase transition was investigated either by perpendicular light scattering and transmission or with a polarized-light microscope. The high-pressure polarized-light microscope allows a precise determination of the melting point. The investigated TAGs showed a significant nonlinear increase of the melting point with pressure. Light scattering and transmission were used to observe the phase change in the high-pressure cell. Similar to supercooling in temperature-induced phase transition, we found a dramatic increase of the delay time in our pressure-induced solidification. Even the dependency of this induction time on the control parameter pressure was similar to that in temperature-driven crystallization. We propose that different crystalline structures may be obtained by superpressuring instead of supercooling.