According to Apple and Pear Australia, the national industry body, Australia’s apple and pear industry produces more fruit for fresh produce consumption than any other fruit industry in Australia and is worth over $580 million annually to the national economy.

As such an important crop and one that is mostly eaten fresh or minimally processed, post-harvest food safety is of critical importance. In this article we reference a recent study entitled: “Food Safety Interventions to Control Listeria Monocytogenes in the Fresh Apple Packing Industry.”

The article covers multiple de-contamination technologies that have all been proven to be effective against Listeria. We have focused this article on Electrolyzed oxidizing water which is the scientific name for eWater Sanitiser.

Overview

After harvest, fresh apples are usually transported to a packing facility, where they are placed in a dump tank, washed, sorted, labeled, and packaged before being shipped for retail sales.

Removal of bacteria from the surface of the apple is difficult due to its morphology. The irregular shape of apples and the presence of micro-structures on the apple peel surface provide ideal conditions for bacterial attachment. Bacteria harboured in these micro-structures may be protected from cleaning interventions.

Food Safety Risk

In 2014, the caramel apple listeriosis outbreak affected 35 people in 12 states across the United States, showing the potential risk of insufficient food safety practices in the apple packing process (CDC, 2015). More recently, in December 2017, a producer of sliced apples recalled fresh apple products due to possible Listeria contamination after a supplier detected Listeria monocytogenes in apple samples during random testing by the FDA.

L. monocytogenes is commonly present in the agricultural environment and fresh produce can be contaminated during growth and harvest.

However, the major sources of bacterial contamination of fresh produce were found in the postharvest operations rather than field conditions (Johnston et al., 2005). L. monocytogenes has the ability to persist in the apple packing facility environment and can result in cross contamination of the fruit, especially during wet processing.

Typical De-contamination Methods

Microbial decontamination methods used in the fresh produce industry can be divided into three main groups:

1. Chemical: including, chlorine, ClO2, PAA, ozone, EOW, H2O2, and essential oils (EOs);

2. Physical: including radiation, ultrasound, and cold plasma (CP); and

3. Biological: including bacteriocins and bacteriophages.

Chemical methods are most commonly used in the decontamination of fresh produce. Significant research has been done to investigate their antimicrobial properties and the mechanism behind their action. Chemical methods are effective and more economically efficient compared to physical and biological methods (Meireles, Giaouris, & Simoes, 2016).

The drawbacks of using chemical disinfectants and sanitizers are potential harmful effects on human health and the environment due to formation of secondary components (chlorine), corrosive effects on the equipment (ozone and PAA) and formation of off-flavours and off-odours.

eWater (EOW) has an effective method

EOW has been reported to be an efficient antimicrobial agent for most food borne pathogens. Most publications associate the antimicrobial potential of EOW with high oxidation reductive potential (ORP) and the presence of biocidal components such O2,Cl2, HOCl, OCl−, and HCl.

In this study, it was found that the concentration of EOW with a lower chlorine concentration had an equivalent antimicrobial activity against L. monocytogenes as a typical chlorine solution containing four times as much free chlorine (180 ppm Cl−). Similar findings were presented by Machado et al. (2016) who reported that slightly acidic EW with a lower concentration of chlorine (30 ppm) was as effective as higher concentrations of the traditional chlorine from NaOCl (80 ppm) in reducing microbial loads on fresh cut vegetables.

Laboratory tests have shown that slightly acidic chlorine EW was also more effective in removing biofilm and preventing biofilm regrowth.

Both studies on slightly acidic EW emphasized numerous advantages of the system such as –

• noncorrosive character

• rapid generation time

• low cost

• lack of Cl2 off-gassing

• lack of residues on produce due to a low concentration of chlorine

Additionally, an EOW system is cost-effective and safe for workers. After the initial investment related to equipment, pro-duction of EOW requires only water and salt (sodium chloride).

In this research paper the author notes that for apple packing operations, EOW could potentially be used for water treatment in dump tanks and flumes to reduce microbial loads and prevent cross contamination. Submersion of produce bins constantly introduces new organic matter into water in dump tanks and flumes. High ORP values of EOW can help maintain the water quality and prevent sudden drops of ORP values under recommended values.

Research Conclusion

Attacking bacteria by using several different mechanisms through hurdle technology may help to improve the apple de-contamination efficiency. Significant research is still needed for the development of effective strategies of reducing microbial loads on fresh apples.

Critical aspects that should be considered include morphological characteristic of apples, conditions and scale of the packing process, and influence of the interventions on apple eating quality.

To review the full research paper - refer to this link