An Increase in Bacterial and Fungal Contamination of Stored Fruit and Vegetables in Supermarkets – Is Light the Real Culprit?

Fruits and vegetables have a strong link to serious food borne disease outbreaks. The Escherichia coli outbreak linked to spinach in 2006, the norovirus gastrointestinal outbreak linked to frozen raspberries in 2005 and 2007, Salmonellosis and E. coli outbreak linked to lettuce in 2005 are worth the mention (Adams et al, 1989).

Though the soil is not a direct source of human pathogens that afflict fruits and vegetables, it is a rich indirect source of contamination mostly from human feces. This may occur by leaching of fecal contaminated water from a septic tank or by percolation of contaminated water from river and lakes in the soil in the vicinity (De Rover, 1998).

Thus, fruits and vegetables in the supermarkets invariably carry dormant human bacterial and fungal pathogens either on their surface or deep within their tissue that go active at every available opportunity.

In such a scenario, exposure to ultraviolet light is a technique employed widely for the disinfection of fruits and vegetables either prior to display or with an additional ultraviolet lamp feature installed in the display racks.

Ultraviolet radiation works by damaging the DNA of these microorganisms forming cytotoxic compounds such as cyclobutane pyrimidine dimers (CPDs).

Recent research evidence has shown that this DNA damage caused by high UV-C irradiation (280 nm) is reversed on subsequent exposure to light that gives out polychromatic emissions and lower wavelength UV (230-240 nm). The non-specific food display fluorescent lamp is a classic example of light producing polychromatic emissions.

This phenomenon is called photo reversal, where, the damaged DNA of the pathogens gets repaired on exposure to polychromatic emissions in multiple wavelengths (Poepping et al, 2014).

Further, there are numerous other problems associated with ultraviolet radiation exposure, especially, the formation of disinfection byproducts (DBPs) such as nitrites from nitrates in the vegetables and fruits (Kalisvaart, 2001).

Apart from the formation of nitrites from nitrates by ultraviolet photolysis, additional nitrites are also formed from the photo activated bacteria that, on consumption, deter and damage the oxygen metabolism in human beings (Sharpless and Linden, 2001; Butler and Feelisch, 2008).

Thus, a non-specific offensive display light can, reduce the shelf life of vegetables and fruits by photo oxidation, affect the quality of beneficial bioactive compounds, bring about changes in temperature within a display rack causing temperature heterogeneity by radiation and rejuvenate the dormant or damaged bacterial and fungal cells, thereby, increasing food spoilage by contamination.

Hence, intelligent lighting is the best way to food display. Recent research has elucidated the effect of selective lighting with specific fluorescent and light-emitting diode (LED green light) on the extended shelf life, visual quality and bioactive compounds in broccoli florets.

The study has shown that selective and specific light treatment could extend the shelf life by protecting the chlorophyll contents in broccoli florets, increasing the total phenols and glucosinolates and improving the radical scavenging activity (Jin et al, 2015).

Promolux offers an assortment of food display fluorescents and LEDs that are specific and selective for vegetable and fruit display, assuring an extended shelf life.


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