Carbohydrate Polymers 87 (2012) 1375–1382 Contents lists available at SciVerse ScienceDirect Carbohydrate Polymers jo u rn al hom epa ge: www.elsevier.com/locate/carbpol Glass transition temperatures of cassava starch–whey protein concentrate systems at low and intermediate water content Lorena García a,b , Aura Cova b , Aleida J. Sandoval b,∗ , Alejandro J. Müller a , Liomary M. Carrasquel c a Grupo de Polímeros USB, Dpto. de Ciencia de los Materiales, Universidad Simón Bolívar, Aptdo. 89000, Caracas 1080-A, Venezuela b Depto. de Tecnología de Procesos Biológicos y Bioquímicos, Universidad Simón Bolívar, Aptdo. 89000, Caracas 1080-A, Venezuela c Depto. de Biología Celular, Universidad Simón Bolívar, Aptdo. 89000, Caracas 1080-A, Venezuela a r t i c l e i n f o Article history: Received 25 June 2011 Received in revised form 31 August 2011 Accepted 9 September 2011 Available online 16 September 2011 Keywords: Glass transition Cassava starch Protein WPC a b s t r a c t Glass transition temperatures of cassava starch (CS)–whey protein concentrate (WPC) blends were deter- mined by means of differential scanning calorimetry (DSC) in a water content range of 8–20% (dry basis, d.b.). Water equilibration in the samples was carried out by storing them at room temperature (25 ◦ C) during four weeks. Physical aging and phase segregation were observed in some samples after this stor- age period depending on the water content. Both, first DSC heating scans and tan ı curves of CS–WPC blends with intermediate water content (10–18%), showed two endothermic thermal events. The first one appeared at around 60 ◦ C and was independent of water content. The second one was detected at higher temperatures and moved towards the low-temperature peak as the water content increased. The results can be explained by a phase segregation process that can take place when the samples are conditioned below their glass transition temperatures. The Gordon–Taylor equation described well the plasticizing effect of water on the blends. WPC was also found to decrease the glass transition temperature, at con- stant water content, an effect attributed to additional water produced during browning reactions in the blends. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction In tropical countries, cassava (Manihot esculenta) root consti- tutes the fourth most produced crop, after rice, wheat and corn. Although an annual average production of 522,000 ton has been reported in Venezuela (Anonymous, 2009a), post-harvest losses are elevated (around 30% of the national production). This fact has been related to the short shelf-life of this crop; between 24 and 48 h after harvesting (González & Pérez, 2003; Soares, Grossmann, Silva, Caliari, & Spinosa, 1999). Consequently, cassava starch has become a potential raw material in different processes (e.g., extrusion cook- ing) in such a way that finished products with higher shelf-life and added value can be obtained. During extrusion, quality of the final product is measured in terms of texture which is established dur- ing expansion at the die end and finished when the exiting cooling melt undergoes glass transition (Della Valle, Vergnes, Colonna, & Patria, 1997; Fan, Mitchell, & Blanshard, 1994; Moraru & Kokini, 2003). Hence, the role that the glass transition temperatures on texture establishment during extrusion processes is very impor- tant and more research on their values are required in order to ∗ Corresponding author. Tel.: +58 212 9063976; fax: +58 212 9063971. E-mail address: asandova@usb.ve (A.J. Sandoval). be able to control both, process and final texture, as suggested for breadmaking (Cuq, Abecassis, & Guilbert, 2003). Besides starchy source, during extrusion process, addition of other ingredients, such as proteins, lipids, water and minor compo- nents like salt, sugar, vitamins, among others, is required. Hence, it is important to gain information about interactions among them. The effect of sodium chloride on the calorimetric glass transi- tion temperature of cassava starch was addressed by Farahnaky, Farhat, Mitchell, and Hill (2009). These authors reported a depres- sion of glass transition temperature of low water cassava starch (water conditioned in an 11% relative humidity environment), from 166 to 135 ◦ C for samples with 0 and 6% of added salt, respec- tively. Madrigal, Sandoval, and Müller (2011) reported the effect of added corn oil on the glass transition of cassava starch. Accord- ing to these authors cassava starch was more plasticized by water when the added corn oil content was lower. They also reported a plasticizing effect of corn oil on cassava starch probably due to hydrophilic–hydrophobic interactions between these two compo- nents. It is well known that whey proteins, mainly composed of - lactoglobulin, -lactalbumin and bovine serum albumin protein fractions (Cayot & Lorient, 1997), have many applications in food industry. Apart from their nutritional efficacy, whey proteins are responsible for the hydration capacity, gelling, forming and emul- sifying properties in different foodstuffs. An increasing interest in 0144-8617/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.carbpol.2011.09.035