Crystallization behavior and crystal properties of lactose as affected by lactic, citric, or phosphoric acid

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 β-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 β-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 β/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 β/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.

Complexities related to the amorphous content of lactose carriers

Although the amount of amorphous content in lactose is low, its impact on the performance of a dry powder inhalation formulation might be high. Many formulators and regulatory agencies believe that the levels of amorphous content should be controlled once there is a relationship with the final product performance. This is however not an easy task. The current paper elaborates on multiple challenges and complexities that are related to the control of the amorphous content in lactose. The definition and quantification methods of amorphous lactose are reviewed, as well as challenges related to thermodynamic instability. Additionally, current monographs and recent position papers considering this parameter are discussed to provide an overview of the regulatory landscape. Development of a control strategy is recommended, provided that the amorphous content at a specific moment in the process has shown to have an impact on the performance of the dry powder inhaler.

Unraveling the Influences of Sodium, Potassium, Magnesium, and Calcium on the Crystallization Behavior of Lactose

The inability of lactose to properly crystallize due to the presence of high amounts of salts poses significant hurdles for its downstream processing with some dairy waste streams such as acid whey. This study aimed to investigate the physicochemical and thermal behaviors of lactose in the presence of cations commonly present in acid whey. A model-based study was conducted, utilizing various cations (Mg, Ca, K, and Na) at concentrations (8, 30, 38, and 22 mM, respectively) that are typically found in acid whey. The research experiments were conducted using a factorial design. The thermal analysis of concentrated solutions revealed augmentation in the enthalpy of water evaporation in the presence of individual cations and their combinations in comparison with pure lactose (698.4 J/g). The degree of enthalpy increased following the order of Na+ (918.6 J/g), K+ (936.6 J/g), Mg2+ (987.0 J/g), Ca2+ (993.2 J/g), and their mixture (1005.4 J/g). This resulted in a substantial crystal yield decline in the exactly reversed order to that of the enthalpy. The greatest decline was observed in the presence of the salt mixture (63%) followed by Ca (67%) compared with pure lactose (79%). The yield reduction was also inversely related to the solubility of lactose. The presence of divalent cations appeared to play a role in the isomerization of lactose molecules observed using DSC and XRD diffractograms according to the disappearance of peaks related to β lactose. The effect of salts on the crystallization of lactose was a combination of cation-lactose interactions, changes in the solubility of lactose, ion-dipole interactions between water and cations, and changes in the structure of water molecules. By deviating the composition of acid whey, the crystallization of lactose can be enhanced, leading to the improved downstream processing of acid whey.

Thermal characteristics of crystalline and amorphous 2'-fucosyllactose, a human milk oligosaccharide

The thermal characteristics of crystalline and amorphous forms of a human milk oligosaccharide, 2'-fucosyllactose (2'-FL), were investigated by differential scanning calorimetry and thermogravimetric analysis, and compared with the two forms of α-lactose monohydrate. Crystalline 2'-FL (87.48% crystallinity according to X-ray diffraction) showed dehydration at 143.4 °C (close to lactose) and melting at 230.6 °C (the same as β-lactose crystal). Amorphous 2'-FL showed glass transition at 127.6 °C and crystallisation at 192.8 °C, which were much higher than the corresponding temperatures for amorphous lactose. 2'-FL showed thermal decomposition at temperatures about 10 °C higher (210-212 °C) than lactose, indicating the higher thermal stability of 2'-FL. Amorphous 2'-FL showed sharp decreases in glass transition (127.6 °C to 36.5 °C) and crystallisation (192.8 °C to 103.4 °C) temperatures with increasing water activity (a_w) from 0 to 0.53, above which no glass transition or crystallisation was observed.