Received 14 May 2014
Received in revised form 4 July 2014
Accepted 11 July 2014
Available online 19 July 2014
Keywords: order to study thermo-mechanical process conditions that allow obtaining whey protein aggregates with tion and break the aggregates (Shewan and Stokes, 2013). This gives
WP particles with specific structural and sensorial properties which are strongly influenced by their structure and size distribution.
These latter depend on physicochemical and thermo-mechanical process conditions as shown in recent studies (Erabit et al., 2013, 2014; Ndoye et al., 2013) and in previous works (Simmons et al., aggregation of widely de unfolding ion. At a temperature and neutral pH, the b-lg is mainly on the f non-covalent dimers (Pessen et al., 1985). For temperature 40 C, the dimers dissociate to monomers. The first step aggregation reaction, which is the best described in literature (Mulvihill and Donovan, 1987; Dannenberg and Kessler, 1988;
Iametti et al., 1996; Hoffmann and van Mil, 1997; Tolkach and
Kulozik, 2007), lead to the reversible loss of the native state by unfolding of the monomers. This step of unfolding occurs at temperature above 60 C and expose thiol groups and hydrophobic areas. The second step is properly the aggregation and takes place ⇑ Corresponding author. Tel.: +33 1 40966161; fax: +33 1 40966075.
E-mail address: email@example.com (F.T. Ndoye).
Journal of Food Engineering 144 (2015) 66–76
Contents lists availab
Journal of Food ls(Foegeding et al., 2002; Shewan and Stokes, 2013). Themicroparticulation is a thermo-mechanical process based on heat treatments (heating, holding at a given temperature and cooling) to denature and aggregate WPs and shear operations to interrupt the aggregaThe mechanism of the thermally-induced b-lactoglobulin (b-lg), the major WP, has been in literature. It is a two steps reaction: reversible monomers followed by irreversible aggregathttp://dx.doi.org/10.1016/j.jfoodeng.2014.07.006 0260-8774/ 2014 Elsevier Ltd. All rights reserved.scribed of the mbient orm of above of theFunctional ingredients derived from whey protein (WP) are widely used in food industry for several specific applications including sensorial and textural improvement (e.g. for healthier food formulations such as reduced fat products), satiety control, encapsulation and controlled delivery of bioactive compounds.
The desired functionalities often guide the type of process (enzymatic, physicochemical or thermo-mechanical) to implement trolled process and reproducible functionality of the heat induced
WPaggregates, it is essential to understand the influence of the thermal process operating conditions on the WP aggregation kinetics.
Besides experimental characterization, modeling can help gain a better control of the WP aggregation process and the functional properties of the aggregates suspension such as the residual native fraction, the aggregate size distribution (ASD) and the viscosity, through a deeper knowledge of the mechanism of WP aggregation.Population Balance Model
Whey protein b-Lactoglobulin
Aggregation 1. Introductionspecific functionalities. The modelling approach aims to describe physico-chemical phenomena (unfolding, collisions and aggregation) occurring during aggregation process and to predict the functional properties of the aggregates suspension after thermo-mechanical treatment. The model is based on
Population Balance Equations and integrates different specific mechanisms of b-lg aggregation through several parameters. These parameters are identified using experimental thermo-mechanical treatments (67–95 C for different holding times) on 6% b-lg solution with CaCl2 added (from 5.1 to 7.1 mM). For this system, the model is able to predict the residual native fraction, the aggregate size distribution and the viscosity of the aggregates suspension. The role of moderate shear in aggregate formation is well represented by the model. The model also describes successfully the effect of variations of the physicochemical environment as it is illustrated with the influence of calcium on the probability of aggregation for large particles. 2014 Elsevier Ltd. All rights reserved. 2007; De Wit, 2009; Nicolai et al., 2011). In order to ensure a con-Article history: A new modelling approach of the thermally-induced aggregation of b-lactoglobulin was developed inA Population Balance Model integrating s of the b-lactoglobulin thermally-induced
Nicolas Erabit a,b,c,d, Fatou Toutie Ndoye a,⇑, Graciela a IRSTEA Refrigeration Process Engineering Research Unit, Antony, France bAgroParisTech, UMR1145 Ingénierie Procédés Aliments, Massy, France c INRA, UMR1145 – Ingénierie Procédés Aliments, Massy, France d Le Cnam, UMR1145 – Ingénierie Procédés Aliments, Paris, France a r t i c l e i n f o a b s t r a c t journal homepage: www.eme specificities ggregation varez a, Denis Flick b,c,d le at ScienceDirect
Engineering evier .com/locate / j foodeng d EnNomenclature
Latin symbols a0 radius of monomers (m) ai radius of aggregates in size class i (m) aj radius of aggregates in size class j (m) ca unfolding constant (K)
Cmon concentration of monomers (g L1)
Cnat concentration of native monomers (g L1)
Cunf concentration of unfolded monomers (g L1)
Cvol cumulative volume size distribution (–)
Df fractal dimension (–)
D[3,2]Glob Sauter mean diameter calculated from simulated results considering monomers and aggregates (m)
D[3,2]LG Sauter mean diameter considering only aggregates in the detection range of the laser granulometer:
P0.1 lm (m) h proportional factor (–)
I total number of size classes (–) k constant of Boltzmann (m2 kg s2 K1) kij total aggregation kernel implying size classes i and j (m3 s1) kperi,ij perikinetic aggregation kernel implying size classes i and j (m3 s1) kortho,ij orthokinetic aggregation kernel implying size classes i and j (m3 s1)
N total number of experimental points
N. Erabit et al. / Journal of Fooat temperature ranging from 70 C to 140 C. It consists on an irreversible phase which involves the formation of disulphide bonds between unfolded monomers resulting in polymers and aggregates. For modeling issue, the aggregation process has been described as a global reaction from native to aggregated state (Dannenberg and Kessler, 1988; Anema and McKenna, 1996) with a temperature dependent kinetic (Arrhenius equation). Two ranges of temperature are generally distinguished depending on which step is limiting, introducing the existence of a transition temperature around 90 C. Kinetic parameters (activation energy and