The effect of temperature and shear upon technological properties of whey protein concentrate: Aggregation in a tubular heat exchanger Fernanda Kerche, Martijn Weterings, Michael Beyrer * Institute Life Technologies, University of Applied Sciences and Arts Western Switzerland, CH-1950 Sion, Switzerland article info Article history: Received 1 November 2015 Received in revised form 12 February 2016 Accepted 13 February 2016 Available online xxx abstract Microparticulation of whey proteins at low concentration (2%, w/v), was examined in a pilot plant tubular heat exchanger (THE). Turbulent flow in combination with moderate temperatures (85  C) was used in the heating section to prevent fouling, whereas the flow was varied from laminar to turbulent in the holding section of the THE. The logarithm of the formal rate of denaturation of b-lactoglobulin (b-Lg) k f was 5.4 to 2.5 depending on the temperature. Variation of flow velocity in the holding section had a negligible impact on denaturation degree of b-Lg and particle size of agglomerates. A high increase of elastic modulus, G 0 , of agglomerates was combined with only bisection of water holding capacity. Advanced modifications of particle structure and properties are supposed to be achievable by more freedom in control of flow character at a heating section of a THE for example through application of direct heat transfer principles. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Whey protein (WP) powders are widely used as ingredients to influence food quality, especially food texture, water holding ca- pacity or emulsion stability. Advanced separation technologies (such as cross flow filtration) enable fractionation, concentration and, in combination with heat treatment, functionalisation of whey components. b-Lactoglobulin (b-Lg) represents about 60% of whey proteins (Edwards & Jameson, 2014). Heat and, more specifically, the time- temperature history of WP concentrate or isolate has the potential to induce agglomeration and microparticulation of b-Lg (Spiegel, 1999; Tolkach & Kulozik, 2007), and is coupled to additional fac- tors of the physicochemical environment such as pH (Dissanayake, Ramchandran, Donkor, & Vasiljevic, 2013; Giroux, Houde, & Britten, 2010; Mehalebi, Nicolai, & Durand, 2008; Spiegel & Huss, 2002), calcium concentration (Erabit, Flick, & Alvarez, 2014; Erabit, Ndoye, Alvarez, & Flick, 2015; Giroux et al., 2010; Spiegel & Huss, 2002), ionic strength (Nicorescu et al., 2008a,b) and whey protein concentration (Dissanayake et al., 2013; Erabit et al., 2014; Mehalebi et al., 2008; Wolz & Kulozik, 2015). Most kinetic studies on microparticulation of whey proteins have been performed at the laboratory scale by indirectly heating a solution in a water bath (Croguennec, O'Kennedy, & Mehra, 2004; Tolkach & Kulozik, 2007) or Couette cell (Erabit et al., 2014; Simmons, Jayaraman, & Fryer, 2007; Steventon, Donald, & Gladen, 1994). A cylindrical, coaxial Couette cell generates a laminar flow in incompressible, viscous liquids and is used in this context to elucidate the impact in the shear rate upon agglomeration kinetics and tailoring of WP. Simmons et al. (2007) observed an increase of size of agglomerates due to a decrease of shear rate from 624 down to 111 s 1 and more specifically a local maximum at about 300 s 1 , when agglomeration was performed at 80  C for 20 min. Erabit et al. (2014) found a positive correlation of shear rate and particle size if agglomeration of b-Lg was carried out at a shear rate from 0 to 400 s 1 . The impact of higher shear on faster heat transfer and thus temperature evolution in the solution was corrected in this study by modelling the temperature in the gap of the Couette cell. Such observations are explained by an increase in collision rate at increasing shear rate, followed by a break-up of agglomerates at shear rates higher than the critical shear rate. However, a shear rate of about 300e400 s 1 might be advantageous in formation of ag- glomerates, but the concept has not yet been screened for heat exchanger geometries as applied in dairy industry. A specific challenge during microparticulation of WP in an in- dustrial operation unit is to prevent fouling during heating (Gu erin, Ronse, Bouvier, Debreyne, & Delaplace, 2007) and enhancing the heat transfer coefficient. Both objectives can be achieved by high shear rates and/or continuing mechanical cleaning of heat exchanger surfaces by blades. Spiegel (1999) reported on * Corresponding author. Tel.: þ41 276068654. E-mail address: michael.beyrer@hevs.ch (M. Beyrer). Contents lists available at ScienceDirect International Dairy Journal journal homepage: www.elsevier.com/locate/idairyj http://dx.doi.org/10.1016/j.idairyj.2016.02.032 0958-6946/© 2016 Elsevier Ltd. All rights reserved. International Dairy Journal xxx (2016) 1e7 Please cite this article in press as: Kerche, F., et al., The effect of temperature and shear upon technological properties of whey protein concentrate: Aggregation in a tubular heat exchanger, International Dairy Journal (2016), http://dx.doi.org/10.1016/j.idairyj.2016.02.032