Effect of homogenizing pressure and sterilizing condition on quality of canned high fat coconut milk

Journal of Food Engineering 73 (2006) 38–44 www.elsevier.com/locate/jfoodeng

Effect of homogenizing pressure and sterilizing condition on quality of canned high fat coconut milk

Naphaporn Chiewchan *

, Chanthima Phungamngoen, Suwit Siriwattanayothin

Department of Food Engineering, King Mongkut s University of Technology, Thonburi, Tungkru, Bangkok 10140, Thailand

Received 31 August 2004; accepted 6 January 2005

Available online 24 February

2005

Abstract

The effect of homogenizing pressure (15–27 MPa) and commercial sterilizing condition (109.3–121.1 C under pressure

of

5–15 psi) on the quality of canned high fat (30%) coconut milk was investigated. All heat-treated homogenized samples

exhibited

pseudoplastic behavior with flow behavior index (n) between 0.719 and 0.971. At similar sterilizing condition, a decrease in n

value

and an increase in consistency index (K) were observed for samples passing higher homogenizing pressures. A reduction in

apparent

viscosity was found for the homogenized samples undergoing higher sterilizing temperatures. For color determination, Hunter

L/b

values of homogenized coconut milk were greater than that for fresh sample and the values increased with increasing pressures.

The

reduction in L/b values was observed when the homogenized samples were subjected to heat treatment. Sterilizing at 121.1 C

for

60 min could provide an acceptable color comparing to fresh coconut milk while heating at lower temperature but for longer

time

permitted more browning reaction and resulted in an increase of b value. Overall, the results suggested that quality of canned

high

fat coconut milk in terms of rheological and optical properties was influenced by both homogenizing pressure and

sterilizing

condition.

2005 Elsevier Ltd. All rights reserved.

Keywords: Coconut milk; Color; Homogenizing pressure; Sterilizing temperature; Rheological properties

1. Introduction

Coconut milk is a milky white oil-in-water emulsion extracted from coconut flesh. It plays an important role in many traditional foods of Asian and Pacific regions. Separation of an emulsion into an aqueous phase and cream phase commonly occurs and leads to an unac- ceptably physical defect of either fresh or processed coconut milk. Canning has been found to be a suitable process for preservation of coconut milk. The process starts from extracting the milk from grated coconut meat with or without added water. The percentage of fat is adjusted before heating at pasteurization tem- perature. The milk is then added with a stabilizer or

* Corresponding author. Tel.: +66 2470 9243; fax: +66 2470 9240.

E-mail address: [email protected] (N. Chiewchan).

emulsifier and pass through the homogenizer. Finally, it was filled in can and sterilized in the retort. Previous research works have demonstrated that fat particle size, dispersion and temperature had significant effects on a stability of foods containing high fat content such as milk, yogurt and cheese (Wasan, Shaker, Jumah, & Jdayil, 2000; Xu, Nikolov, Gonsalves, & Borwankar, 1998). For typical canned coconut milk process, the addition of suitable emulsifiers and homog- enization for reducing fat globule size are required prior to heat treatment to retain the emulsion stability. Sringam (1986) reported that type and quality of emulsifier and homogenization affected the stability of coconut milk. Increasing homogenizing pressure from 1000 to 5000 psi resulted in increasing stability of coco- nut milk and two-stage homogenization at 1000 and 2000 psi resulted in greater stability of coconut

milk

0260-8774/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2005.01.003