Spray drying is a key unit operation in the manufacturing of dairy powders. During the spray drying process, a liquid feedstock is transformed into a dried particulate form through atomising the feed into the hot gas within a drying chamber. An inefficient spray drying operation of dairy products may lead to non-compliant product quality (e.g., stickiness, wall deposition and caking), nutritional losses due to Maillard reaction and substantial economic losses. Therefore, improvement of product quality and minimising the potential problems during the spray drying process are the major concerns of dairy powder manufacturers. Optimisation of spray drying processes for dairy powders can involve a high level of trial and error. In addition, optimisation of the spray drying process through empirical tests are usually expensive, time-consuming and sometimes unreliable. Therefore, there has been an appeal for a shift from empirical efforts toward rational design of spray-dried dairy powders based on a better understanding of the interplays between the process parameters of the spray drying process and dairy powders quality.
Quality by Design (QbD) represents a systematic approach to building quality into process development and manufacturing practices from the outset. QbD is a new paradigm in the food industry, inspired by the Process Analytical Technology (PAT) concept introduced originally for the pharmaceutical industry in 2004 by the Food and Drug Administration (FDA, 2004; Munir et al., 2015). The hypothesis behind this paradigm shift is that the quality of the food products can and should be incorporated into process design and not by post-production quality measurements. Process optimization can be implemented by the use of a combination of QbD tools such as Design of Experiments (DoE) and Response Surface Methodology (RSM). DoE is a structured and systematic approach for determination of critical quality attributes that could affect the process or product in order to ensure their reliability and robustness. Likewise, RSM is applied to describe correlations between independent variables (input) and response variables (output), enabling improved understanding of the influence of different excipients and their interactions, as well as improved prediction of optimized process conditions leading to the desired profile. The knowledge of the interplay between process parameters and quality attributes will enable rational process design to achieve the desired outcome.
The physical properties of dairy powders are governed by the size, distribution and shape of the individual particles making up the powder (Dodds, 2013). The shape, structure, and properties of the particles are heavily influenced by the spray drying operational conditions. Evaluating and tuning of drying parameters based on a more reliable accurate process maps is helpful in dealing with several critical issues in powder handling and product quality due to the undesired changes in particle properties. This study is aimed at optimising the spray drying process parameters for production of skim milk powder using the DoE and RSM as QbD tools. The influence of the spray drying process parameters including inlet air temperature, feed flow rate and the total solid content of feed on outlet air temperature, yield, particle size, moisture content and bulk density were investigated. Spray drying experiments are performed using a laboratory-scale spray dryer fitted with an ultrasonic nozzle (Büchi 290, Switzerland). The spray-dried skim milk powders are characterized by Laser Diffraction Particle Size Analyzer, Scanning Electron Microscopy (SEM) and Thermogravimetric Analysis (TGA). In order to determine the optimum level of spray dryer system parameters leading to the best response, graphical and numerical optimisation procedures are carried out. The experimental design matrix, data analysis, and optimisation procedure are performed using Minitab Statistical Software (Version 17). This study shows the applicability of QbD approach for the enhanced production of spray-dried dairy powders. Use of DoE and RSM results in reduced process variability, higher percentage yields, less treatment time with minimum costs.
Dodds, J., (2013). 13 - Techniques to analyse particle size of food powders A2 - Bhandari, Bhesh, in: Bansal, N., Zhang, M., Schuck, P. (Eds.), Handbook of Food Powders. Woodhead Publishing, pp. 309-338.
FDA, United States Food and Drug Administration, (2004). Guidance for industry: PAT - A framework for innovative pharmaceutical development, manufacturing and quality assurance. Rockville, USA: U.S. Department of Health and Human Services.
Munir, M.T., Yu, W., Young, B.R., Wilson, D.I., I2C, (2015). The current status of process analytical technologies in the dairy industry. Trends in Food Science & Technology 43(2), 205-218.