Effects of ozone exposure on the xerophilic fungus, Eurotium amstelodami IS-SAB-01, isolated from naan bread ☆ Sanjay Antony-Babu ⁎, Ian Singleton Institute for Research on Environment and Sustainability, School of Biology, Devonshire Building, Newcastle University, NE1 7RU, England, United Kingdom abstract article info Article history: Received 19 April 2010 Received in revised form 7 September 2010 Accepted 23 September 2010 Keywords: Naan bread Eurotium Ozone Oxidative stress Sucrose Spores Ascospores Cleistothecia Xerophilic moulds cause contamination and spoilage of low moisture foods. This study examined the effect of ozone fumigation on growth of a Eurotium species isolated from naan bread. Two ozone treatments were used — a low-level long-term exposure (0.4 μmol/mol for 21 days) and high-level short-term exposure (300 μmol/mol for 5 to 120 min). For the low level exposure the combination of different media sucrose concentrations (0, 5, 10 and 20% w/v) with ozone treatment was also assessed. The growth of the isolate was found to be sensitive to low-level ozone fumigation depending on the media sucrose concentration and duration of the exposure. Low-level ozone exposure significantly (p b 0.05) reduced the number of asexual spores formed in media with no added sucrose, an effect not observed in media with higher sucrose levels. Electron microscope observations of colonies indicated that ozone exposed cultures produced lower numbers of cleistothecia. High-level ozone exposure for short durations reduced spore viability although 100% reduction in viability was achieved only after 120 min exposure. This work demonstrates that ozone may be used to reduce spore production in Eurotium but that the ozone effect can be mediated by sucrose levels in the growth medium. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Xerophilic moulds are common food spoilage organisms of low moisture food such as bakery products (Abellana et al., 1999; Hocking and Pitt, 1980; Samson, 1989; Vega et al., 1998), dried fruit (Pitt and Christian, 1968) and grain flours (Beuchat and Hwang, 1996). Eurotium, a well known xerophilic fungal genus, can account for 1 to 5% loss of bakery products along with Aspergillus and Penicillium depending on the season, type of product and method of processing (Malkki and Rauha, 1978). Xerophilic organisms are well known to be tolerant to several external stresses such as desiccation (Vaamonde and Fernández, 1993), salt/sugar concentrations, pH (Guynot et al., 2002), osmotic pressure (Christensen et al., 1965; Garg and Yadav, 2007) and heat (Splittstoesser et al., 1989). Therefore preventing spoilage caused by these organisms poses a major challenge in the food industry. Increased awareness of the harmful effects caused by use of pesticides in food has led to interests in cleaner residue free technologies (Eom, 1994; Schafer and Kegley, 2002; Wilson and Otsuki, 2004). Ozone is well known as a strong oxidising agent and can cause elevation of reactive oxygen species in living cells leading to oxidative stress in the cells. This effect has been harnessed for preservation of food, especially fresh produce (Barth et al., 1995; Liew and Prange, 1994; Tzortzakis et al., 2008). Recent work has been carried out to explore the efficiency of ozone treatment in preserva- tion of low moisture foods (Al-Ahmadi et al., 2009; Najafi and Khodaparast, 2009). Nevertheless very little is known on the direct effect of ozone fumigation on fungal survival and development (Antony-Babu and Singleton, 2009; Tzortzakis et al., 2008) and to our knowledge no work has examined the effect of ozone exposure on xerophilic fungi. The work presented in this paper aimed to explore the effects of ozone on Eurotium amstelodami IS-SAB-01 isolated from naan bread. The potential use of ozone fumigation in food storage facilities was assessed using a low-level long term (21 days) exposure study on media containing different sucrose levels, whereas the ability of ozone to kill the fungus was examined using high level ozone exposure for short periods (0 to 120 min). 2. Materials and methods 2.1. Source of isolate The fungal isolate used in this study was obtained from mouldy naan breads (after the normal shelf-life period). The surface of naan bread was scraped using a sterile inoculation loop and the fungal propagules transferred onto the surface of Rose-Bengal agar (Fluka, UK) plate. This isolation media was used initially to isolate a wide variety of spoilage moulds. The plates were incubated at 28 °C for 21 days. An isolate which was morphologically identified as Eurotium sp. was used in this study. International Journal of Food Microbiology 144 (2011) 331–336 ☆ GenBank accession number related to the paper: GU808560. ⁎ Corresponding author. Tel.: +44 191 246 4855; fax: +44 191 222 5228. E-mail address: Sanjay.Antony@nancy.inra.fr (S. Antony-Babu). 0168-1605/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ijfoodmicro.2010.09.019 Contents lists available at ScienceDirect International Journal of Food Microbiology journal homepage: www.elsevier.com/locate/ijfoodmicro