Monitoring Viscosity and Total Solids Content of Milk Protein Concentrate Using an Inline Acoustic Flowmeter at Laboratory Scale.

Archana Bista,Colm P O’Donnell,John T Tobin,Norah O’Shea

doi:10.3390/foods9091310

Abstract

Control of milk concentrate viscosity and total solids (TS) content prior to spray drying can improve dairy ingredient manufacture. However, the availability of hygienic and appropriately pressure rated process viscometers for inline monitoring of viscosity is limited. An acoustic flowmeter (FLOWave) is an inline process analytical technology (PAT) tool that measures changes in acoustic signals in response to changes in liquid properties (i.e., acoustic transmission (AT), acoustic impedance (AI), temperature and volume flowrate). In this study, an acoustic flowmeter is evaluated as an inline PAT tool for monitoring viscosity of milk protein concentrate (MPC85), protein and TS content of (MPC85), and standardised MPC (sMPC). Laboratory scale experiments were carried out at 45 °C for five different concentrations (4–21%) of MPC85 and sMPC. Results showed that AT decreased with an increase in MPC85 viscosity (e.g., AT was 98.79 ± 0.04% and 86.65 ± 0.17% for 4% and 21% TS content, respectively). Non-linear regression was carried out to develop a relationship between AT and offline viscosity (R2 (coefficient of determination) value = 0.97 and standard error of prediction = 1.86 mPa·s). AI was observed to increase at higher protein and TS content which was dependent on protein to total solid ratio (P_TSR). Multiple linear regression was carried out to develop the relationship between AI, protein content, TS content and P_TSR. Results demonstrated that AI could be used to monitor the protein and TS content of milk protein concentrate (R2 > 0.96). Overall this study demonstrated the potential of an inline acoustic flowmeter for monitoring process viscosity, protein and TS during dairy concentrate processing.

Highlights

The milk protein concentrate (MPC) powder manufacturing process involves a combination of various processes, such as membrane separation techniques, through which non-protein constituents are extensively removed from skim milk followed by evaporation and spray drying [1]
Overall this study demonstrated the potential of an inline acoustic flowmeter for monitoring process viscosity, protein and total solids (TS) during dairy concentrate processing
Non-linear regression was performed on the experimental data to develop prediction equations, and statistical evaluation of equations were carried out using the coefficient of determination (R2 ), standard error of prediction (SEP), error sum of squares (SSE), root mean square error (RMSE), Bayesian information criterion (BIC) and Akaike information criterion (AIC) to predict the relationship between apparent viscosity and acoustic transmission (AT) [25]

Summary

Introduction

The milk protein concentrate (MPC) powder manufacturing process involves a combination of various processes, such as membrane separation techniques, through which non-protein constituents (e.g., lactose and minerals) are extensively removed from skim milk followed by evaporation and spray drying [1]. MPC powder is used in a wide range of food applications, i.e., dairy beverages [2], cheese [3] and high protein nutritional bars [4]. The rate-limiting effect of viscosity associated with a high protein content of liquid MPC, reduces the evaporative capacity to ~30% total solids (TS) for MPC70, compared to skim milk concentrate (SMC) which can be concentrated to >50% TS prior to spray drying [5]. Many laboratory viscometers currently available have limitations, i.e., measurements are time-consuming, not suitable for rapid real-time monitoring of concentrate viscosity and may not. Some limitations of conventional viscometers can be overcome by inline viscosity measurements that monitors concentrate viscosity in real-time for improved process control [10]. O’Sullivan et al [16] calculated inline viscosity during the reconstitution of milk powders (skim milk powder and milk protein isolate) using the

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