Anthocyanin degradation kinetics during thermal and high pressure treatments of raspberries Lise Verbeyst, Kim Van Crombruggen, Iesel Van der Plancken, Marc Hendrickx, Ann Van Loey ⇑ Laboratory of Food Technology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (M2S), Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, Box 2457, B-3001 Heverlee, Belgium article info Article history: Received 5 August 2010 Received in revised form 11 February 2011 Accepted 14 March 2011 Available online 21 March 2011 Keywords: Anthocyanins Raspberry Thermal processing High pressure processing Degradation kinetics abstract The effect of combined high temperature and high pressure on the degradation of the four main cyanidin- 3-glycosides in raspberries was investigated. Anthocyanin degradation accelerated with increasing tem- perature as well as with increasing pressure, revealing a synergistic effect of both process variables. Deg- radation rate constants were estimated using a first order kinetic model. Temperature and pressure dependence of the degradation rate constants were expressed as activation energies and activation vol- umes according to Arrhenius and Eyring equations, respectively. In search of statistical differences between the E a –k ref - and V a –k ref -parameters estimated simultaneously, 90% joint confidence regions were constructed. A combined Arrhenius–Eyring model was found suitable to describe the combined temper- ature–pressure dependence of the degradation rate constants. Cyanidin-3-glucorutinoside showed the slowest degradation in comparison to the other cyanidins. Cyanidin-3-rutinoside experienced the small- est effect of temperature and the strongest effect of pressure compared to the others. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction In order to meet growing consumer demands, food scientists explore new technologies and try to optimise existing ones. High pressure processing is an alternative preservation technique to thermal processing and has already proven its value in pasteurisa- tion processes. Applying high pressures (up to 600 MPa) at ambi- ent temperature results in microbiologically safe products which can be stored for a considerable time at 4 °C, whilst valuable food characteristics, such as flavour, colour, texture, nutrients are re- tained (Cheftel, 1995; Matser et al., 2004; Oey et al., 2008). Indus- trial applications include production of fruit juices, guacamole, etc. (Matser et al., 2004; Norton and Sun, 2008). High pressure sterili- sation is still a challenge. For inactivation of spores, high pressures in combination with high temperatures seem to be necessary (Black et al., 2007; Wilson et al., 2008). The impact of those high temperatures in combination with high pressures on the quality of the food product then becomes an issue. Nevertheless, a high pressure sterilisation process could be advantageous with regard to reducing process times and thus reducing process impact, be- cause pressure build-up starts at relatively moderate temperature and adiabatic compression is used to reach the desired process temperature fast (Matser et al., 2004). Research on the simultaneous effect of high temperatures and high pressures on nutritional and quality parameters of foods is thus indispensable. In this study, the issue of anthocyanins in rasp- berries is dealt with. Raspberries are good sources of anthocyanins and often used to prepare juices, jams, ice cream, etc. Anthocyanins are important pigments in fruit, vegetables and flowers, providing red, blue and purple colours. Their chemical structure comprises of a flavonoid skeleton, varying in hydroxyl- and/or methoxyl-sub- stituents, making up the anthocyanidin; glycosylation of the anthocyanidin forms the anthocyanin (Castaneda-Ovando et al., 2009; Clifford, 2000). Four anthocyanins predominate in the vari- ety of raspberries studied here (Rubus idaeus, cv. Sugana); they are all cyanidin-compounds with different sugar moieties at- tached: sophoroside, glucorutinoside, glucoside and rutinoside (de Ancos et al., 1999; Maatta-Riihinen et al., 2004). Furthermore, anthocyanins are known for their potent antioxidant power and their possible contribution to prevent chronic diseases such as can- cer and heart disease (Kong et al., 2003; Zafra-Stone et al., 2007). As anthocyanins are promising natural food colorants and health-promoting compounds, their unstable nature unfortunately constitutes an obstacle towards practical applications. Their stability can be affected by several factors such as pH, temperature, light, oxygen, enzymes (Castaneda-Ovando et al., 2009). Tempera- ture is known to have a deleterious effect on anthocyanins (e.g. Harbourne et al., 2008); the influence of pressure was only recently studied. A group of researchers found no direct effect of pressure treatments (200–800 MPa, for 15 min, at 18–22 °C) on 0260-8774/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2011.03.015 ⇑ Corresponding author. Tel.: +32 16321585; fax: +32 16321960. E-mail address: ann.vanloey@biw.kuleuven.be (A. Van Loey). Journal of Food Engineering 105 (2011) 513–521 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng