Effect of whey protein concentration on the fouling and cleaning of a heat transfer surface Adel Fickak, Ali Al-Raisi, Xiao Dong Chen ⇑ Biotechnology and Food Engineering Group, Department of Chemical Engineering, Monash University, Clayton Campus, Victoria 3800, Melbourne, Australia article info Article history: Received 11 March 2010 Received in revised form 4 November 2010 Accepted 10 November 2010 Available online 28 December 2010 Keywords: Cleaning-in-place (CIP) Fouling Heat induced gels Dissolution Dairy processing abstract In the studies of fouling and cleaning of heat exchange surfaces in dairy plants, whey protein deposits and heat induced whey protein gels (HIWPG) are considered as suitable model material to simulate the pro- teinaceous based type ‘‘A’’ milk fouling. Protein concentration of the fouling solution may significantly influence the formation of milk deposits on heat exchange surfaces, hence affecting the cleaning effi- ciency. In this study, a laboratory produced heat induced whey protein gels (HIWPG) and a pilot plant heat exchanger fouling/cleaning were used to investigate the effect of protein concentration on formation and cleaning of dairy fouling. Here, HIWPGs made from different protein concentrations were formed in capsules and then dissolved in aqueous sodium hydroxide (0.5 wt%). The dissolution rate calculation based on the UV spectrophotometer analysis. In the pilot-scale plant study, whey protein fouling deposits were formed by recirculating whey protein solutions with different concentrations through the heat exchange section in different runs, respectively. The deposit layers were then removed by recirculating aqueous sodium hydroxide (0.5 wt%) and the cleaning efficiency was monitored in the form of the recov- ery of heat transfer coefficient while both fluid electric conductivity and turbidity were monitored as indications of cleaning completion. It was found that increasing the protein concentration of the HIWPG significantly increased the gel hardness and the dissolution time. In addition, increasing the protein con- centration significantly increased both, the amount of the fouling on the pilot-scale plant and the time required to clean the fouling deposit. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction During the thermal processing of dairy products, deposit layers are often formed on the process surface of the heat exchangers. The cleaning, or removal, of such deposits is crucial for quality and safety issues. Cleaning using chemicals is costly, both economically and environmentally (Toyoda et al., 1994). The fouling and clean- ing of proteinaceous deposits have received considerable attention due to their importance in the dairy industries (Visser, 1997). In the last decades, the understanding of the fouling and cleaning processes in dairy plants has been considerably improved (Fryer et al., 1996a; Wilson et al., 1999, 2002; Chen et al., 2004). The ma- jor components in dairy fouling deposits are the heat-sensitive whey proteins (Visser, 1997). In fact aggregated whey protein mol- ecules dominate the basic structure of the fouling deposits. Be- cause of this and also the complex nature of milk deposits, many researchers (Belmar-Beiny et al., 1993; Schreier et al., 1994; Del- place and Leutiet, 1995; Fryer et al., 1996b; Davies et al., 1997; Gillham et al., 1999; Chen et al., 2000, 2001; Xin et al., 2002a,b), found heat induced whey protein gels (HIWPG) to be a reliable model system for investigating milk fouling and cleaning. Heat induced whey protein gel (HIWPG) also contain a small quantity of minerals and have been found to have the same nature of type ‘A’ milk deposits described by Lyster (1965) and Burton (1968), where proteins represent more than 60 wt% of the deposit mass. The formation of the HIWPG deposits results from the aggre- gation of whey proteins upon heating. At the time a HIWPG is formed, only a fraction of the whey proteins has aggregated (Ver- heul and Roef, 1998a,b). The magnitude of this fraction, as well as the gel point, depends on many factors such as the gelation pH, temperature and protein concentration (Mulvihill et al., 1990; Langton and Hermansson, 1992; Renard and Lefebvre, 1992; Verheul and Roef, 1998a). HIWPG with high protein concen- tration tend to form faster due to the increasing rate of aggregation and the decreasing coagulation time (Sharma and Hill, 1993). A Study by Mleko (1999) has found that increasing the protein con- centration will increase the firmness and the aggregate size of WPC gels, accelerating the gelation process. Furthermore, a study by Puyol et al. (2001) found that WPI gels with high protein concen- tration tend to form at lower temperature. 0260-8774/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2010.11.004 ⇑ Corresponding author. Tel.: +61 3 99059344; fax: +61 3 99055686. E-mail address: dong.chen@eng.monash.edu.au (X.D. Chen). Journal of Food Engineering 104 (2011) 323–331 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng