Effect of Diffusion on Component Segregation During Drying of Aqueous Solutions Containing Protein and Sugar

Abstract

Water content profiles within thin aqueous films of lactose and bovine serum albumin (BSA) were tracked during drying using inverse microscope Raman spectroscopy (IMRS). These film drying experiments provide useful insights into component diffusion within droplets during spray drying in the food industry. Virtually no segregation of lactose and BSA occurred in the films during drying at 30 C. Thus, in film drying simulations at this temperature, lactose and BSA can be assumed to be a single homogenous solute, and binary diffusion of water and this single solute can be modeled. A solute-fixed coordinate system drying model properly predicted the water content profiles and shrinkage of the films during the constant rate period. This represents a partial validation of the model. The drying model predicted significant gradients in water content in films dried at a higher temperature of 80 C, which have the potential to drive segregation of lactose and BSA. However, IMRS analysis of films dried at 80 C revealed no segregation of lactose and BSA. We propose that lactose and BSA are relatively immobile in the bulk of the film during drying, forming a homogenous gel that allows the significantly smaller water molecules to diffuse through. The observed accumulation of BSA as a monolayer at the surface of the dried films appears to be a local phenomenon most likely driven by the surface activity of BSA.

Evolution and Morphology of Thin Films Formed by Solvent Evaporation: An Organic Semiconductor Case Study

“…Experimentally, the initiation of film growth with the formation of a skin at the vapor interface has been observed during the formation of polymer films by evaporation as well as during the drying of aqueous solutions of proteins and sugars. 32,33 Not only does the loss of solvent at the interface appear to trigger the nucleation of the skin but once formed, the skin moderates the subsequent rate of evaporation, as has been reported previously for simulation studies of solvent evaporation from polymer solutions. 7 As the skin is forming (0 μs < t < ∼0.2 μs), the rate of evaporation decreases rapidly together with the fraction of the surface occupied by chloroform.…”

Recent advances in drying at interfaces of biomaterials

“…Recently, ATR-FTIR spectroscopy is used to gain more insight into the film forming mechanism during drying of solutions of pullulan and alginate [131]. Inverse microscope Raman spectroscopy has been applied to measure water content in films [132].…”

Exploring the protein adsorption behavior at the droplet/air interface during drying of composite protein/sugar droplets

“…As a typical ingredient segregation phenomenon, this property has often been used to control the stickiness of powders composed mainly of sugars [2]. A number of theories have been developed to explain the segregation, attributing it to the surface activity of proteins, the different diffusivities between proteins and sugars, the atomization process, etc [3][4][5][6]. In this study, we investigated the adsorption process of sodium caseinate (NaCas) at the surface of a NaCas/lactose droplet, without and with drying.…”