Effect of repeated heating and cooling cycles on the pasting properties of starch Hayfa Salman, Les Copeland * Faculty of Agriculture, Food and Natural Resources, University of Sydney, NSW 2006, Australia article info Article history: Received 30 March 2009 Received in revised form 8 September 2009 Accepted 12 October 2009 Keywords: Starch Rapid Visco Analyser Pasting properties Starch–lipid complexes abstract The properties of starch and starch–lipid pastes have been explored using a novel extended Rapid Visco Analyser (RVA) profile, in which the heating and cooling cycles are repeated five times. Starches from four wheat varieties with amylose content ranging from 23 to 27%, and waxy starches of wheat, rice and maize were tested, alone and in mixtures with lauric acid and monopalmitin (glyceryl-1-monopalmitin). Gels of all of the starches formed and melted reproducibly during repeated heating and cooling in the RVA. The addition of lauric acid to the waxy starches had no effect on the multiple RVA profile. Monopalmitin caused an increase in viscosity during the heating stage of the second to the fifth cycles with the waxy starches, which was attributed to the presence of monopalmitin aggregates. Changes in the multiple cycle viscosity traces observed when monopalmitin or lauric acid was added to the amylose- containing starches were complex. It was concluded that RVA paste viscosities were determined by starch–lipid interactions, as well as by free lipid in the starch mixtures. The water solubility of the lipid and association of proteins with starch granules influence these interactions. Ó 2009 Elsevier Ltd. All rights reserved. 1. Introduction Starch is a macro-constituent of many foods and a major source of energy in the human diet. It is also an important industrial material, with about 60 million tonnes extracted annually world wide from cereal, tuber and root crops for food, pharmaceutical and non-edible uses. Starch varies greatly in form and functional properties between and within plant species, and being able to predict functionality for a wide range of end uses from knowledge of the structure remains a significant challenge in food science and nutrition. Most starch consumed by humans has undergone some form of processing, usually involving heating in water with shear, and then cooling. During gelatinization with heat treatment, native starch granules swell and lose their crystallinity and structural organization before collapsing to release the constituent amylose and amylopectin molecules into the aqueous medium. On cooling, the dispersed starch molecules form a gel, which retrogrades gradually into a new semi-crystalline order that differs greatly from native granules (Copeland et al., 2009). Retrogradation of starch is an important determinant of the water absorption and retention properties and digestibility of starch-rich processed foods. The functionality of starch is also modified by interactions with lipids. For example, complexation with lipids reduces the solubility of starch in water, alters the rheological properties of pastes, retards retrogradation and reduces the susceptibility to enzymic hydrolysis. The viscoelastic behavior of starch pastes is often monitored in a Rapid Visco Analyser (RVA), which is a heating and cooling viscometer that measures the resistance of a sample to controlled shear (Crosbie and Ross, 2007). The RVA is an empirical instrument which provides a convenient way to compare the effect of additives on the viscoelastic properties of starch pastes (Deffenbaugh and Walker, 1989; Ravi et al. 1999; Tang and Copeland, 2007). Most commonly, a simple heat-hold-cool RVA profile is used to provide comparative information on starch parameters that are useful to food processors. The present study explores the properties of starch and starch–lipid pastes using a novel extended RVA profile, in which the heating and cooling cycles are repeated five times. Starches from four wheat varieties with amylose content ranging from 23 to 27%, and waxy starches of wheat, rice and maize were tested, alone and in mixtures with the water soluble C 12 fatty acid lauric acid, and monopalmitin (glyceryl-1-monopalmitin) a common ingredient in bakery products. 2. Experimental 2.1. Materials Grains from wheat (Triticum aestivum L.) varieties Sunco, Sun- soft, SM1118 and SM1028 were obtained from the Value Added Wheat CRC Ltd. (North Ryde, NSW, Australia). Sunsoft is a soft * Corresponding author. Tel.: þ61 2 9036 7047; fax: þ61 2 9351 2945. E-mail address: l.copeland@usyd.edu.au (L. Copeland). Contents lists available at ScienceDirect Journal of Cereal Science journal homepage: www.elsevier.com/locate/jcs 0733-5210/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jcs.2009.10.004 Journal of Cereal Science 51 (2010) 105–109