food and bioproducts processing 9 3 ( 2 0 1 5 ) 166–175 Contents lists available at ScienceDirect Food and Bioproducts Processing j ourna l h omepage: www.elsevier.com/locate/fbp Cleaning studies of coconut milk foulants formed during heat treatment process P. Saikhwan ∗ , S. Thongchan, N. Jumwan, P. Thungsiabyuan, J. Sakdanuphap, S. Boonsom, P. Kraitong, P. Danwanichakul Department of Chemical Engineering, Faculty of Engineering, Thammasat University, 99 Paholyothin Road, Klongluang, Pathumthani 12121, Thailand a b s t r a c t To elucidate cleaning of coconut milk foulants, swelling and dissolution of model coconut milk foulants found in batch and continuous heat treatment processes were investigated. The model coconut milk foulants were immersed in aqueous sodium hydroxide (NaOH) solutions at pH range of 7–12. Both model deposits showed little swelling at pH less than 10; increasing pH beyond 10 resulted in a rise of extent of swelling. Proteins and fats in the deposits were removed by NaOH solution. Although some components in the deposits could not be removed by soaking the deposit in NaOH, swollen deposits were less cohesive. Strength of swollen deposits was measured using fluid dynamic gauging (FDG) technique and it was found that the strength decreased with increasing pH of NaOH solution (shear stresses reduced from ∼5 to ∼3.5 Pa). Hence, using NaOH solution at appropriate pHs could improve the cleaning efficiency of coconut milk foulants. However, the strength of the deposit formed from a continuous heat treatment process, which was stronger than that obtained from a batch process, could not be measured using FDG (normal stress ∼800 Pa, shear stress ∼30 Pa). This suggests that other cleaning agents or cleaning conditions should be adopted in cleaning of the deposit formed during continuous heat treatment. © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. Keywords: Cleaning; Coconut milk; Fluid dynamic gauging (FDG); Fouling, Swelling 1. Introduction Coconut milk is an oil-in-water emulsion obtained from aque- ous extract of coconut meat. Moisture and fat are major components in coconut milk and the reported composition (in wt%) are: moisture, 54.1; fat, 32.2; protein, 4.4 and car- bohydrate, 8.3 (Popper et al., 1966). Coconut milk is used in traditional Asian dishes and is available worldwide in vari- ous forms. In order to preserve coconut milk, heat treatment is required. For instance, pasteurization involves heating the milk to temperature of 72 ◦ C for 20 min (Seow and Gwee, 1997) whereas ultra-high temperature (UHT) treatment of coconut milk requires heating the milk at 121 ◦ C for 20 min (Arumughan et al., 1993). Deposits form on heating surfaces during heat treat- ments of food products and daily cleaning is generally usual (Changani et al., 1997). Cleaning or removal of deposit lay- ers from equipment surfaces is observed in two modes: (i) ∗ Corresponding author. Tel.: +66 0 898914807. E-mail address: psaikhwan@engr.tu.ac.th (P. Saikhwan). Received 20 April 2013; Received in revised form 16 December 2013; Accepted 24 December 2013 Available online 4 January 2014 cohesive breakdown where rupture is at deposit–deposit bonds and (ii) adhesive breakdown where rupture is at deposit–substrate bonds resulting in a clean substrate. Sim- ilar to other processes, equipment fouled with coconut milk deposits is usually cleaned by a combination of chemical and mechanical methods. First, the deposit is softened by the action of cleaning solution, and then is removed by a mechan- ical action such as scouring and pigging. Alkali solutions are common in cleaning of food soils as they are known to break down proteins (Lelieveld et al., 2003) and saponify triglycerides found in fat into water soluble fatty acid salts (Plett, 1985; Fryer and Asteriadou, 2009). In addition to alkali solution, large amount of surfactant content and elevated temperature are used in cleaning of triglycerides (Jurado-Alameda et al., 2012; Cunault et al., 2013). Other cleaning agents used in cleaning of fatty food soils are enzymes and ozone (Jurado-Alameda et al., 2012). Cleaning of coconut milk deposits is also done by alkali solution. Nevertheless, the cleaning is poorly understood and 0960-3085/$ – see front matter © 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.fbp.2013.12.011