C: Food Chemistry Effect of Thermal Processing on the Degradation, Isomerization, and Bioaccessibility of Lycopene in Tomato Pulp Ines Colle, Lien Lemmens, Sandy Van Buggenhout, Ann Van Loey, and Marc Hendrickx Abstract: Thermal processing affects the nutritional value of food products. The nutritional value is not only determined by the content but also by the bioaccessibility of nutrients. The present study was performed to gain detailed insight into the influence of thermal processing on the degradation, isomerization, and bioaccessibility of lycopene isomers in tomato pulp, without adding any other ingredient. The bioaccessibility, which is defined as the fraction of the nutrient that can be released from the food matrix, was measured using an in vitro method. The results demonstrated the rather high thermal stability of lycopene. Although a treatment at 140 ◦ C induced isomerization, the contribution of cis-lycopene to the total lycopene content remained small. Results also confirmed that thermal processing as such can improve the in vitro bioaccessibility of lycopene in tomato pulp, but the improvement was only significant upon treatments at temperatures of 130 and 140 ◦ C. At such intense process conditions, one should be aware of the negative effect on other quality and nutrient parameters. Possibilities of thermal processing as such to improve the nutritional value of tomato pulp (without the addition of other ingredients) thus looks rather limited. Keywords: degradation and isomerization, in vitro bioaccessibility, lycopene, thermal processing, tomato pulp Introduction The nutritional value of food products has become one of the top priorities for the food industry. Consumers’ demand for healthy convenience food products is still growing. In past decades, lycopene has attracted attention because of its potential beneficial role for human health. Different epidemiological studies suggested an inverse relationship between diets rich in lycopene and the risk of chronic diseases (Rao and Agarwal 1999; Bramley 2000) including different types of cancers (Giovannucci 1999) and car- diovascular diseases (Willcox and others 2003). Lycopene is a symmetrical, acyclic carotenoid with 13 double bonds of which 11 are conjugated. Because of its characteristic structure, lycopene is an effective antioxidant (Di Mascio and oth- ers 1989; Conn and others 1991). In principle, each double bond of the lycopene polyene chain can exist in 2 configurations, giving rise to 1056 possible isomers (Zechmeister 1962). However, only a limited number of cis-isomers occur in nature. These cis-isomers might be of particular interest because they show higher antiox- idant capacity than all-trans-lycopene (B ¨ ohm and others 2002). Furthermore, the anticarcinogenic effects of lycopene have also been associated with nonoxidative mechanisms (Zhang and others 1991; 1992; Matsushima-Nishiwaki and others 1995; Kobayashi and others 1996; Fuhrman and others 1997; Krutovskikh and others 1997). Since humans are unable to synthesize lycopene de novo, suffi- cient uptake from the diet is necessary to benefit from its health MS 20100153 Submitted 2/11/2010, Accepted 8/18/2010. Authors are with Lab. of Food Technology and Leuven Food Science and Nutrition Research Centre (LFoRCe), Dept. of Microbial and Molecular Systems (M 2 S), Katholieke Univ. Leuven, Belgium. Direct inquiries to author Hendrickx (E-mail: Marc.Hendrickx@ biw.kuleuven.be). promoting effects. The main sources of lycopene in the west- ern diet are tomatoes and tomato-based products. Among tomato products, juice, ketchup, soup, and sauces are the major contribu- tors in the diet (Bramley 2000). One of the typical unit operations during their production is thermal treatment. On the one hand, it is well known that as a consequence of thermal processing nutrients might be lost. Previous studies demonstrated that lycopene is rather thermally stable in tomato-based food systems during mild ther- mal treatments (Khachik and others 1992; Nguyen and Schwartz 1998; Thompson and others 2000; Nguyen and others 2001), while more intense thermal treatments can cause lycopene degra- dation reactions (Sharma and Le Maguer 1996; Takeoka and others 2001; Graziani and others 2003; Shi and others 2003; Mayeaux and others 2006). In addition, several studies have investigated isomerization of all-trans-lycopene during food processing. How- ever, controversy still exists (Xianquan and others 2005). Nguyen and Schwartz (1998), Nguyen and others (2001), and Seybold and others (2004) only found limited lycopene isomerization dur- ing thermal processing of tomato products. However, the results of Dewanto and others (2002) and Shi and others (2003) clearly indi- cated the formation of cis-lycopene during the thermal treatment of tomato puree. On the other hand, it has been suggested that processing of tomatoes increases the bioavailability of lycopene (Stahl and Sies 1992; G¨ artner and others 1997; Porrini and others 1998; van het Hof and others 2000). However, no systematic data are available on the lycopene bioavailability in tomato as a func- tion of processing time and temperature. Since the fraction of an ingested nutrient that can be used by the human body is of major importance, it is a real challenge to identify processing conditions resulting in maximal overall nutrient bioavailability (a balance be- tween lycopene losses and improved bioavailability). In tomatoes, lycopene occurs as carotenoid–protein complexes or membrane bound semicrystalline structures derived from plastids (Shi and Le C  2010 Institute of Food Technologists R  doi: 10.1111/j.1750-3841.2010.01862.x Vol. 75, Nr. 9, 2010  Journal of Food Science C753 Further reproduction without permission is prohibited