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- Materials and methods
Aims: To evaluate the efficacy of sanitizing green coconuts (Cocos nucifera L.) through the treatment applied by juice industries using sodium hypochlorite and peracetic acid.
Methods and Results: The surface of the fruits was inoculated with a mixture of five Listeria monocytogenes strains. The treatments consisted in immersing the fruits for 2 min at room temperature in sodium hypochlorite solution containing 200 mg l−1 residual chlorine at pH 6·5, and 80 mg l−1 solution of peracetic acid or sterile water. Bacterial populations were quantified by culturing on trypticase soy agar supplemented with yeast extract and Oxford selective culture medium; however, recovery was higher on the nonselective medium. Immersion in water produced a reduction in the L. monocytogenes population of 1·7 log10 CFU per fruit, while immersion in sodium hypochlorite and peracetic acid solutions resulted in population reductions of 2·7 and 4·7 log10 CFU per fruit respectively.
Conclusions: The treatments studied are efficient to green coconuts.
Significance and Impact of the Study: Sanitation of green coconut is one of the most important control measures to prevent the contamination of coconut water. This article provides information that shows the adequacy of sanitizing treatments applied by the juice industries.
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- Materials and methods
Coconut water is a refreshing beverage much appreciated in tropical countries, especially in coastal areas. On the international market, coconut water has an all-natural appeal, in addition to a wide array of alleged functional benefits (Hollingsworth 2000). In Brazil, processed coconut water have been commercialized with the McDonald’s brand on the box (Kohler 2008). However, the sensory characteristics of fresh coconut water are considered much superior to the overall flavour profile of the processed beverage (Frassetti et al. 2003; Abreu et al. 2005).
Traditionally, coconut water is consumed directly from the fruit after sectioning out a centre hole to access the juice. However, because of difficulties to transport and cut the fruit open, unprocessed coconut water is often extracted, refrigerated and conveniently filled into retail containers. However, during this process, the juice is contaminated because of the direct contact with the epidermis of the coconuts and equipment surfaces (Walter et al. 2009).
The chemical composition of coconut water, with its high levels of sugars and mineral salts (Jayalekshmy et al. 1986), pH value above 4·5 and water activity close to 1·0, provides favourable conditions for microbial growth. Escherichia coli and Salmonella have been detected in cold-stored in natura (that is, fresh, unprocessed) coconut water (Melo et al. 2003), in addition to Staphylococcus aureus populations of up to 8·0 × 104 CFU ml−1 (Hoffmann et al. 2002) and Bacillus cereus counts of 1·6 × 105 CFU ml−1 (Leite et al. 2000). Fortes et al. (2006) analysed 20 samples of unprocessed coconut water in plastic bottles and found that none met the minimum microbiological requirements set forth in Brazilian legislation. Our previous work showed the development of Listeria monocytogenes in coconut water stored at 4, 10 and 35°C (Walter et al. 2009).
Listeria monocytogenes is a psychrotrophic and ubiquitous pathogen (Fenlon 1999; Gandhi and Chikindas 2007). This pathogen presents a high mortality rate among some high risk groups, including the newborn, the aged and people with compromised immune systems (Slutsker and Schuchat 1999). These people and pregnant women choose to consume coconut water because of its natural isotonic appeal and other claimed therapeutic properties. Despite no Listeriosis outbreaks associated with the consumption of coconut water have been found, vegetables have been recognized to harbour L. monocytogenes (Fröder et al. 2007; Little et al. 2007; Chen et al. 2009) or have been associated with listeriosis outbreaks (Schlech et al. 1983; Varma et al. 2007). The risk for coconut contamination by L. monocytogenes is increased because of the agricultural practices. During harvest the fruits are placed directly on the soil, the natural habitat of L. monocytogenes. In addition, during fresh coconut water processing, there is no lethal step between extraction and packaging that assures beverage microbial safety. Furthermore, L. monocytogenes has the ability to survive for longer periods under adverse environmental conditions when compared to nonsporeforming pathogenic bacteria relevant to public health (Fenlon 1999; Gandhi and Chikindas 2007), in addition to being more chlorine resistant than Salmonella and E. coli O157:H7 (Burnett and Beuchat 2000).
Chlorinated compounds, particularly hypochlorites, are widely used in microbial control and have along history of application in the food processing industry (Wei et al. 1985). In addition to their economic benefits, hypochlorites are effective in inactivating micro-organisms suspended in water and on nonporous surfaces (Brackett 1987). However, on the surface of fruits and green leafy vegetables, their efficacy is rather limited (Burnett and Beuchat 2000). Other negative side effects are associated with the formation of potentially toxic compounds that contaminate the environment (Wei et al. 1985; Richardson 2003). Peracetic acid appears as an alternative to chlorinated compounds because of its higher efficiency and lower pollution potential, in spite of its higher costs.
The objective of this study was to evaluate the efficacy of sodium hypochlorite and peracetic acid in eliminating L. monocytogenes artificially inoculated onto the surface of green coconuts.