Changes in quality attributes throughout storage of strawberry juice processed by high-intensity pulsed electric fields or heat treatments Ingrid Aguilo ´-Aguayo, Gemma Oms-Oliu, Robert Soliva-Fortuny, Olga Martı ´n-Belloso * Department of Food Technology, UTPV-CeRTA, University of Lleida, Rovira Roure 191, 25198 Lleida, Spain article info Article history: Received 30 June 2008 Received in revised form 24 November 2008 Accepted 27 November 2008 Keywords: High-intensity pulsed electric fields Strawberry juice Color Viscosity abstract The effects of high-intensity pulsed electric field (HIPEF) processing (35 kV/cm for 1700 ms applying 4-ms pulses at 100 Hz in bipolar mode) on color, viscosity and PME and PG activities in strawberry juice were studied and compared to those of heat treatments (90  C for 60 s or 30 s) through 63 days of storage. L * and viscosity values of the HIPEF-processed juices were higher than those found in the thermally treated. In addition, HIPEF-treated juice exhibited lower 5-(hydroxymethyl)-2-furfural (HMF) concentration and browning index than heat-treated juices throughout storage. On the other hand, HIPEF-treated juice maintained low residual pectin methylesterase (PME) activity (13.1%) for 63 days, whereas in the case of the thermally treated, 22.2 and 48.8% was retained after 60 s and 30 s, respectively. Strawberry juice treated by HIPEF achieved lower residual polygalacturonase (PG) activity (73.3%) than those of heat-processed at 90  C for 60 s (76.2%) or 30 s (96.8%). Thus, HIPEF could be a feasible alternative to thermal processing to minimize browning and viscosity loss in strawberry juice during storage. Ó 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. 1. Introduction Consumers are currently demanding fresh, healthy and flavourful ready-to-eat foods with enhanced shelf life (Hayes, Smith, & Morris, 1998). Thermal processing is the most common method for extending the shelf life of juices, by inactivating microorganisms and enzymes. Nevertheless, concomitant losses in terms of flavor, color, sensory and nutritional qualities occur when foods are heat treated (Goodman, Fawcett, & Barringer, 2002). The attractive red color of strawberry juice is a commercially valued property that is highly degraded due to heat processing (Rodrigo, Van Loey, & Hendrickx, 2007). The negative effects of thermal treatments include non-enzymatic browning, which mainly cause changes in color and formation of undesirable prod- ucts such as 5-(hydroxymethyl)-2-furfural (HMF) (Ibarz, Paga ´n, & Garza, 1999). The formation of HMF is triggered by temperature and time and thus, it is used to evaluate overprocessing in thermal pasteurization (Lee & Nagy, 1988). Viscosity is an important quality attribute limiting the consumer acceptability of fruit juices that can be determined by factors such as the cultivar of fruits or the maturity of the fruit at the moment of processing (Tiziani & Vodovotz, 2005). The decrease in viscosity can be catalyzed by the action of enzymes such as pectin methyl- esterase (PME) and polygalacturonase (PG) (Crelier, Robert, Claude, & Juillerat, 2001). The degradation of pectin substances by both enzymes results in a reduction of the ability of a juice to hold its solid portion in suspension throughout storage (BeMiller, 1986; Chou & Kokini, 1987). High-intensity pulsed electric field (HIPEF) is a nonthermal food-processing technology which uses short bursts of electricity (microseconds to milliseconds), providing fresh-like and safe foods and reducing quality losses that can be triggered after thermal processing (Dunn, 2001; Morris, Brody, & Wicker, 2007). HIPEF has been demonstrated to be an alternative pasteurization method, even though its effects on enzymes and other parameters can vary depending on the product to be processed. Efficiency of HIPEF treatments to inactivate enzymes commonly present in fruit juices has been compared with that of heat treatments (Min, Jin, & Zhang, 2003; Rivas, Rodrigo, Martı ´nez, Barbosa-Ca ´ novas, & Rodrigo, 2006). In contrast, extending the shelf life of juices by HIPEF-processing, while keeping natural or appealing color and viscosity is still being a major challenge. Elez-Martı ´nez, Soliva-Fortuny, and Martı ´n-Bel- loso (2006) reported that HIPEF treatments best maintained the color of orange juice for 56 days of storage compared with thermal processing. In addition, Aguilo ´-Aguayo, Soliva-Fortuny, and Martı ´n- Belloso (2008) observed that HIPEF resulted in higher tomato juice PME and PG inactivation than heat treatment. Moreover, they reported an increase in the viscosity of the HIPEF-processed juice. The scarce literature available about HIPEF-treated strawberry juice is only referred to its microbiological commercial shelf life (Mosqueda-Melgar, Raybaudi-Massilia, & Martı ´n-Belloso, 2008). Therefore, the purpose of this study was to evaluate the effects of * Corresponding author. Tel.: þ34 973 702 593; fax: þ34 973 702 596. E-mail address: omartin@tecal.udl.es (O. Martı ´n-Belloso). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt 0023-6438/$34.00 Ó 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2008.11.008 LWT - Food Science and Technology 42 (2009) 813–818