A method of producing microparticles of the type having a crosslinked, aggregated protein matrix by spray drying

Abstract

A method of producing microparticles by spray drying comprises the steps of providing a spray-drying feedstock solution comprising water, a volatile divalent metal salt, weak acid, 5-15% dairy or vegetable protein (w / v) and 1-20% active agent (w / v). The feedstock solution is adjusted to have a pH at which the volatile divalent metal salt is substantially insoluble. The feedstock solution is then spray-dried at an elevated temperature to provide atomised droplets, whereby the volatile divalent metal salt disassociates at the elevated temperature to release divalent metal ions which crosslink and aggregate the protein in the atomised droplets to produce micro-particles having a crosslinked aggregated protein matrix and active agent dispersed throughout the matrix.

Description

TECHNICAL FIELD[0001]The invention relates to method of producing microparticles by spray drying, especially microparticles of the type having a crosslinked and aggregated protein matrix in which the protein is of dairy or vegetable origin.BACKGROUND TO THE INVENTION[0002]The disintegration of liquid into small droplets have long been a significant field of research interest, due to two reasons: (1) to apply to a liquid in some unit operations (particularly drying, cooling or freezing) and 2) to produce granular / capsular materials that offer some advantages such as stability, ease of dosing / handling and specific processing surface characteristics. This disintegration of liquid into droplets is evident in the field of micro-encapsulation where a core material (i.e. bioactive) is inserted or entrapped in a matrix (for example, WO2010119041) for improved bioactive protection, product yield and also to facilitate subsequent production processes. Examples of such encapsulation methods in...

AI Technical Summary

Benefits of technology

The patent describes a method for producing microparticles with high levels of active agents. The method involves using a liquid feedstock solution that includes protein, acid, and a crosslinking agent in an inactive precursor form. This precursor form is activated in the elevated temperature conditions of the drying chamber to release the divalent metal crosslinking agent which crosslinks and aggregates the protein at the atomised droplet stage. The use of a hydrocolloid in the feedstock increases the solids content and strength of the microparticles, while also preventing moisture migration. The method achieves higher levels of active agent yield in the microparticles compared to previous methods.

Problems solved by technology

While this method produces spherical, homogenously-sized microdroplets that are capable of gastric transit intact, the process involves use of specialised vibrating nozzle machinery which represents an additional expense for food companies.

Furthermore, the drying of microbeads generated by the technology WO2010119041 is not easily achieved using spray drying technology since the relatively large size of the micro-beads causes a disruption of the atomisation processes.

Hence, micro-bead trajectories must be kept away from the drying chamber wall for longest time possible to allow correct drying; however this is not practically possible for commercial spray-drying scenarios.

However, the readjustment of shear stresses within the liquid once the droplet is airborne is another factor contributing to further disintegration of the droplet / microparticle.

This is again a limitation for microbead technologies using spray-drying.

One possible solution to this problem is replacement of an atomiser nozzle in a spray dryer with a vibrating nozzle, however this approach resulted in large droplets that stuck to the dryer wall (FIG. 2).

A further possible solution is to add a cross-linking agent to the liquid feedstock with a view to making larger spray-dried particles that consist of cross-linked protein, however this results in cross-linking of the protein in the feedstock liquid prior to atomisation, with a resultant increase in viscosity and in most cases gelation of the feedstock liquid making it impossible to atomise the feedstock solution.

Moreover, as alginate is such a strong gelling agent, only very low amounts can be employed in spray-drying feedstock which means that the total solids of the resultant microparticles is quite low, resulting in less polymerisation of the matrix and consequently a weaker and less stable matrtix, reduced yield of active agent (cargo) during drying, and less control of particle size.

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