Synergistic effect of sonication and high osmotic pressure enhances membrane damage and viability loss of Salmonella in orange juice E. Wong a , F. Vaillant-Barka b, ⁎, E. Chaves-Olarte c a Centro Nacional de Ciencia y Tecnología de Alimentos, Universidad de Costa Rica, San José, Costa Rica b UMR QUALISUD, Centre International de Recherche Agronomique pour le Développement (CIRAD), Avenue Agropolis, TA50/PS4, 34398 Montpellier Cedex 5, France c Centro de Investigación en Enfermedades Tropicales, Facultad de Microbiología, Universidad de Costa Rica, San José, Costa Rica abstract article info Article history: Received 9 June 2010 Accepted 29 July 2010 Keywords: Ultrasound Concentration Osmosonication Membrane damage Food safety Fruit juice The efficacy of using sonication (50 ± 0.2 W, 20 kHz), combined with subsequent concentration and storage at high osmotic pressure, has been evaluated to reduce levels of Salmonella bacteria in different solutions (PBS, sucrose and orange juice) at varying concentrations. To visualize the impact on cell membranes, we used a staining protocol (propidium iodide [PI] and 4′,6′-diamidino-2-phenylindole [DAPI]). Sonication alone did not cause significant membrane damage. Storage alone, for 48 h and at high osmotic pressure (10.9 MPa), affected membrane permeability in 20% of cells. However, sonication, combined with storage, considerably increased loss of membrane integrity, resulting in a significant logarithmic reduction of microorganisms. When the combination was applied to contaminated orange juice, a 5 log 10 cfu ml -1 reduction of Salmonella spp. was obtained. “Osmosonication”—the synergistic combination of sonication and subsequent storage at high osmotic pressure—is an innovative alternative for the non-thermal decontamination of liquid foods. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Of all fruits, orange is the most processed by the beverage industry worldwide (Tiwari, Muthukumarappan, O'Donnel & Cullen, 2008), with more than 50% of juices in international commerce corresponding to citrus fruits (Varnam & Sutherland, 1999). Probably because of the reduced time spent in preparing food in modern households, the consumption of fresh citrus in recent years has decreased while the consumption of processed juice has increased (Ros-Chumillas, Belissario, Iguaz, & López, 2007). Meanwhile, con- sumers still seek a healthy life style and demand ever more natural products that are minimally processed. Unfortunately, as the consumption of minimally processed fruit juice increased so has the number of outbreaks of foodborne illnesses (CDC, 2000). Minimally processed orange juice has frequently been identified as the source of pathogenic bacteria in several of these outbreaks, most related to Salmonella species (Birkhead, Morse, & Levine, 1993; CDC, 1999; Cook & Dobbs, 1998; Duncan, Doull, Millar, & Bancroft, 1946; Eisenstein, Aach, Jacobson, & Goldman, 1963; Krause, Terzagian, & Hammond, 2001; Singh, Kulshreshtha, & Kapoor, 1996; Tabershaw, Schmelzer, & Bruyn, 1967). The fruit juice industry therefore faces the challenge of develop- ing and using alternative minimal processes that guarantee food safety and food quality and freshness. These quality aspects are crucial for orange juice mainly consumed for its contribution to the daily intake of essential vitamins that must be preserved during processing (Meléndez-Martínez, Escudero-Gilete, Vicario, & Her- edia, 2010; Penicaud, Peyron, Bohuon, Gontard, & Guillard, 2010). Consequently, agro-industries are increasingly interested in inno- vative non-thermal processing alternatives. The main requirement for such alternatives is that they reduce the pathogen load in food to a minimum of 5 log 10 , as recommended by the U.S. Food and Drug Administration (FDA, 2001). One potential alternative—sonication—is an emerging technolo- gy that has already been used in combination with other processing steps to reduce microbial loads in food products (Levandowsky, 1981; Piyasena, Mohareb, & McKellar, 2003). Combined with heat (thermosonication), pressure (manosonication) or both (thermo- manosonication), sonication acts synergistically to reduce the time, temperature and pressure required in processing (Lee, Zhou, Feng, & Martin, 2009; Pagan, Manas, Alvarez, & Condon, 1999; Walkling- Ribeiro, Noci, Cronin, Lyng, & Morgan, 2009; Wu, Gamage, Vilkhu, Simons, & Mawson, 2008). Sonication appears to weaken microbial membranes through cavitation induced by ultrasonic shock waves (Butz & Tauscher, 2002), thereby making microorganisms more vulnerable to external stresses (Levandowsky, 1981; Pagan, Manas, Raso, & Condon, 1999; Piyasena et al., 2003; Ulusoy, Colak, & Hampikyan, 2007). Food Research International 45 (2012) 1072–1079 ⁎ Corresponding author. Tel.: +33 4 67 61 55 19; fax: +33 4 67 61 55 15. E-mail addresses: eric.wong@ucr.ac.cr (E. Wong), fabrice.vaillant@cirad.fr (F. Vaillant-Barka), esteban.chaves@ucr.ac.cr (E. Chaves-Olarte). 0963-9969/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.foodres.2010.07.037 Contents lists available at ScienceDirect Food Research International journal homepage: www.elsevier.com/locate/foodres