Carbohydrate is one among the four major classes of biomolecules. It serves as an important energy source in plants and animals. Lactose is the only carbohydrate naturally found in mammalian milk. It is widely used in dairy powders, food ingredients and pharmaceutical formulations. The presence of lactose in these products often related to stickiness and caking which cause blockages in pharmaceutical tableting machines and reducing the shelf-life of food ingredients by forming solid lumps. Appropriate size, shape, physical state, packing and flow characteristics of lactose crystals are essential for the food and pharmaceutical applications because a small change in these parameters can affect the overall performance of the product. Crystallization plays a vital role in controlling the size and morphology of lactose crystals. In our present work, the effect of supersaturation, time taken for the generation of supersaturation and volume of the solution on the size, morphology and crystallization kinetics of α-LM single crystals in aqueous solution was investigated. A range of supersaturation σ=0.05-1.30 was generated in 100 mL of α-LM aqueous solution at 307 K by employing slow evaporation process. While adopting this process, the induction time for the occurrence of nucleation was found to be varying from 131 h to 127 h. Size of the nucleated crystals varying from 80-60 µm in the supersaturation range σ=0.05-1.30. From the beginning to the end of the growth process, α-LM crystals were retaining the tomahawk morphology and there was no change observed in the entire ranges of supersaturation σ=0.50-130. A similar range of supersaturation σ=0.05-1.30 was generated in 500 µL of α-LM aqueous solution at 307 K by employing fast evaporation process. During this process, the induction time for the crystallization of α-LM was found to be greatly reduced and it was varied from 1.2 h to 0.03 h. By fast evaporation process the nucleations with tomahawk morphology was obtained initially at the lower supersaturation range σ=0.05-0.50, crystals with triangular morphology was obtained in the range σ=0.51-0.90 and crystals with triangular as well as diamond-like morphologies were observed in the supersaturation range σ=0.90-1.30. During growth, it was found that the morphology of the nucleated crystals changes from tomahawk to pyramidal shape with beveled faces at the bottom (within 65 min from the beginning of the nucleation) in the supersaturation range σ=0.05-0.50. Whereas the triangular morphology of the crystal changes to trapezoidal (within 35 min from the beginning of the nucleation) at the supersaturation range of σ=0.51 to 0.90. During growth there was a morphological change from diamond-like morphology to needle shape. Size of the nucleated crystals varies from 30 to 10 µm. Variation in the growth rate of different faces of the crystals at different supersaturation levels was found to be due to the difference in the strength of the intermolecular interactions between the respective faces and the solvent molecules. The nucleation kinetics of primary nucleated α-LM crystals were studied on the basis of classical nucleation theory. From the calculated values of nucleation parameters it was observed that only one type of nucleation is possible in all ranges of supersaturation from σ=0.05 to σ=1.30 while employing both the slow and fast evaporation process. In both the processes, similar range of supersaturation σ=0.50-1.30 was generated at different intervals of time and with difference in volume of the mother solution. Size and morphology of α-LM crystals were found to be varying with the different operational parameters employed. It is concluded that by optimizing the operational parameters, the size and morphology of α-LM crystals can be controlled to achieve the desired physico-chemical properties.

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