Improving Process Yield by Adding WPI to Lactose During Crystallization and Spray Drying Under High-Humidity Conditions

Abstract

This paper reports to dry and crystallize lactose in one process: spray drying. In order to achieve this, conditions in the spray-drying process have been optimized to create a high-humidity environment that promotes crystallization, and Whey Protein Isolate (WPI) has been added as a drying aid to increase the yield. In this study, low concentrations of WPI have been added to the lactose feed in order to maintain a high level of lactose purity in the final product, as well as enhancing crystallization by reducing the negative effects of protein addition in delaying the onset of crystallization. In a Buchi B-290 spray dryer, the introduction of WPI at only 0.5% (solid basis) concentration as a drying aid to increase the yield of spray-dried lactose was successful in increasing the yield from 20% to 60% in high-humidity drying conditions. XPS (X-ray photoelectron spectroscopy) results show that approximately 50% (by mass) surface coverage by WPI was obtained when the bulk concentration of WPI was only 0.5 wt%. Furthermore, the high-humidity, high-temperature drying environment utilized in the experiments enhanced the crystallization process. The spray-dried materials produced in these experiments displayed crystalline characteristics of high peak intensity counts during X-ray diffraction, lower moisture sorption peak heights, lower heats of crystallization, low glass-transition temperatures in thermal analysis using MDSC, and distinct signs of crystallization on the particle surfaces as observed from SEM imaging. It can be suggested that, at this “critical” concentration (0.5 wt%), WPI has the potential to promote high yields (more than 50%) of crystallized spray-dried lactose under the right conditions (65–70% relative humidity of the drying gas and inlet-gas temperature 210°C) with small-scale spray dryers, such as the Buchi B-290 used here.

Keywords:

• Lactose crystallization
• Particle surface
• Solid-phase crystallization
• Spray drying
• Surface composition
• Whey protein

ACKNOWLEDGMENT

The authors would like to thank Natasha Ali from the School of Chemical and Biomolecular Engineering of The University of Sydney for her contribution performing part of the spray-drying experiments as presented in this work.

Notes

All values are mean ± standard deviation of at least two replicate analyses.

For each property, means in a row followed by different letters (a–c) are significantly different at p = 0.05.

*NA: not available.

All values are mean ± standard deviation of at least two replicate analyses.