Fouling behavior of coconut milk at pasteurization temperatures Phavanee Narataruksa a, * , Waraporn Pichitvittayakarn b , Peter J. Heggs c , Suvit Tia d a Department of Chemical Engineering, Faculty of Engineering, King Mongkut’s University of Technology North Bangkok, 1518 Pibulsongkram Road, Bangsue, Bangkok 10800, Thailand b The Joint Graduate School of Energy and Environment, King Mongkut’s University of Technology Thonburi,126 Prachautid Road, Bandmod, Tungkru, Bangkok 10140, Thailand c School of Chemical Engineering and Analytical Science, The University of Manchester, Manchester M60 1QD, United Kingdom d Department of Chemical Engineering, Faculty of Engineering, King Mongkut’s University of Technology Thonburi, 126 Prachautid Road, Bandmod, Tungkru, Bangkok 10140, Thailand article info Article history: Received 11 August 2008 Accepted 26 February 2010 Available online 11 March 2010 Keywords: Fouling Coconut milk Pasteurization abstract Fouling by coconut milk at different heating temperatures (50e54.5  C, 60e64.5  C, and 70e74.5  C) and at three volumetric flows (2,4 and 6 LPM) in a test section equipped with four flat plates was studied. Measurement of the overall heat transfer coefficient (U) and the compositions of deposit mass were completed in order to obtain fouling factors (R f ) and an empirical model for the rate of increase of Biot number (ΔBi/Δt) as a function of the temperature (T) and the flow (F). The results illustrated that the fouling factor increased, when the temperature fell due to a combination of chemical reaction fouling from proteins and precipitation fouling from fat. The fouling factor also increased, when the flow was lowered due to a slow rate of deposit removal introduced by small shear force. Combination of the two effects revealed that the effect of flow was less significant at higher temperatures. All results can be confirmed by an analysis of fouling compositions. At high temperature conditions, more denaturation of proteins resulted in less ability to entrap fat globules onto heating surface. The heat resistance was found decreasing with increasing temperature. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Coconut milk is the word used to present the liquid obtained by mechanical force of coconut meat normally with added water. This kind of milk is an important ingredient in many Asian and Pacific food dishes. To be preserved, coconut milk in canned and dehy- drated forms is well known in the world market. However, for domestic consumption, pasteurized coconut milk in soft plastic bags has more freshness and is more convenient for cooking. The short-term preservation process starts with the extraction of the milk from coconut meat with added water. The percentage of fat is adjusted depending upon local requirement, which can be between 15 and 40%. In the pasteurization process, the milk is heated to pasteurization temperature of between 72 and 75  C for 20 min [1]. The pasteurized coconut milk has a shelf-life of not more than 5 days at 4  C [2]. The heating process normally takes place in a system of indirect plate heat exchangers, which consists of pre- heating, heating, and cooling sections. Since the coconut milk is a complex biological fluid, typically composed of fat, protein, carbohydrates, and minerals as a white oil-in-water emulsion, some components can lose their rheological properties and/or denature to form deposits on the heating surfaces. The deposit formation on the heat exchanger surfaces in this case is called coconut milk fouling. Unlike fouling from dairy products, the rate of deposit build up is more rapid. Characteristic of the deposit formation is also unique. Without the information on the rate of fouling affected by process variables, the plant efficiency is rapidly decreased with time and, therefore costs are drastically increased. Previous research investigations have concentrated mainly on fouling from dairy products. Burton [3] reported that the cow milk fouling deposit is a Type A for the pasteurization process and is a white and voluminous deposit made up of protein (50e60%), minerals (30e35%) and fat (4e8%). The type A deposit starts to form when the temperature reaches about 70  C. Gotham [4] stated that at this temperature, most of the protein is denatured b-lactoglob- ulin at or near the heating surface leading to deposit formation due to chemical reaction fouling. The deposit can be found for run times greater than 1 h. The type A deposit consists of a protein-rich outer layer and a mineral-rich inner layer near the heat exchanger surface [5e8]. However, Burton [9] suggested that fat was found to act as an insignificant factor in the deposit formation in the indirect heating systems of cow milk. The rate of food fouling is usually a strong function of process variables, it is important to understand the effects of variations in the system parameters on the rate of fouling. The characteristic of fluid is the first factor. Skudder, Brooker, Bonsey & Alvarez-Guerrero * Corresponding author. Tel.: þ66 2 913 2500x8230; fax: þ66 2 587 0024. E-mail address: phn@kmutnb.ac.th (P. Narataruksa). Contents lists available at ScienceDirect Applied Thermal Engineering journal homepage: www.elsevier.com/locate/apthermeng 1359-4311/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.applthermaleng.2010.02.028 Applied Thermal Engineering 30 (2010) 1387e1395