Balsamic vinegar from Modena: An easy and effective approach to reduce Listeria monocytogenes from lettuce

Highlights

• Comparing with water, all solutions were capable of reducing the pathogen counts.

• Balsamic vinegar showed the best antilisterial activity from the solutions tested.

• Listeria inhibition followed a linear reduction with balsamic vinegar concentration.

• Balsamic vinegar antilisterial activity can be linked to phenol compounds and pH.

Abstract

The microbiological safety of fresh produce is a significant concern of consumers and industry. After applying at an inoculated level (6–7 log CFU/mL) of Listeria monocytogenes on Iceberg lettuce, the antilisterial properties of balsamic vinegar from Modena, white wine vinegar and acetic acid solutions were investigated.

Different proportions of the vinegars, acetic acid (58.7 g/L), and deionized water were evaluated to determine the role of those solutions at the stage of washing Iceberg lettuce to remove L. monocytogenes. The maximum observed log reduction of L. monocytogenes was 2.15 ± 0.04 for balsamic vinegar (50% (v/v)), 1.18 ± 0.06 for white wine vinegar ((50% (v/v)) and 1.13 ± 0.06 for acetic acid ((50% (v/v)). Washing with water only reduces 0.05 ± 0.04 log CFU/mL of L. monocytogenes numbers.

Listeria reductions observed for balsamic vinegar are similar or higher than those of chlorine-based sanitizers evaluated in other studies with lettuce. In the case of balsamic vinegar solutions, Listeria inhibition followed a linear reduction according to the model: Log (N/N₀) = −4.09 × balsamic vinegar proportion % (v/v) − 0.13; R² = 0.95. Balsamic vinegar washings may be a promising method for reducing other foodborne pathogens present in produce or other foods, at home and retail environments.

Introduction

The incidence of foodborne infections caused by bacterial pathogens continues to be a problem in industrialized nations and developing countries (Chang and Fang, 2007, Ramos et al., 2013). Bacteria most frequently linked to food outbreaks are Salmonella spp., Escherichia coli, Listeria monocytogenes and Shigella spp. (Rico et al., 2007, Senorans et al., 2003, Warriner, 2005).

Gastrointestinal disease caused by L. monocytogenes is rare compared to other agents of foodborne illness, but invasive listeriosis can be very severe and has a high fatality rate (Little et al., 2007, Miller et al., 2009a, Nastou et al., 2012). This pathogen is considered ubiquitous in nature environment and produce is likely to be contaminated (Sant'Ana, Igarashi, Landgraf, Destro, & Franco, 2012).

Several studies have reported that the occurrence of L. monocytogenes in ready-to-eat vegetables in several parts of the world may be as high as 25% (Cordano and Jacquet, 2009, Crepet et al., 2007, Sant'Ana et al., 2012). This is of special concern because this kind of food is likely to be consumed raw, relying only on cold storage to maintain their safety, but Listeria has the ability to survive and multiply at refrigeration temperatures (Luber et al., 2011, Miller et al., 2011).

Vegetable consumption has grown over the last two decades, especially lettuce that on average is eaten by a third of the population once a week (Doménech, Botella, Ferrús, & Escriche, 2013). Raw vegetables have been identified as a vehicle of transmission of foodborne outbreaks and play an important role in listeriosis epidemiology. Improper temperature control, poor cleanliness and inappropriate refrigerator management have been identified as critical factors in foodborne listeriosis (Luber et al., 2011, Ramos et al., 2013, Sant'Ana et al., 2012).

Proper food handling at home can maintain the hazard at a safe level and even reduce it. Thus, it is important to develop strategies to control L. monocytogenes in the home environment (Doménech et al., 2013, Shen et al., 2009).

Retail environments also play a role in the contamination of foods and/or amplification of L. monocytogenes, however linking a specific retail environment to an outbreak of infection is difficult to prove (Varma et al., 2007). Interventions directed at home and retail environments may be an important way to reduce sporadic disease, which represents the greatest burden of L. monocytogenes infection (Varma et al., 2007).

In the home or restaurant, fewer options are available for effective washing of vegetables than in a modern processing plant. There are various chemical compounds available in these environments that can be useful for sanitizing fresh produce, particularly vinegar which contains acetic acid (Shen et al., 2009, Yang et al., 2009).

Vinegar and vinegar-based solutions are commonly used as dressings for salads and appetizers and have been studied with favourable results for their efficacy in removing pathogens from fresh fruits and vegetables (Chang and Fang, 2007, Sengun and Karapinar, 2004, Shen et al., 2009, Vijayakumar and Wolf-Hall, 2002). In addition, consumers are increasingly avoiding consumption of foods treated with preservatives of chemical origin and so vinegar solutions can be an appealing natural alternative (Sengun & Karapinar, 2004).

The purpose of this study was to determine the antimicrobial activity of vinegar solutions on L. monocytogenes inoculated onto lettuce. With this aim in mind, inactivation of this microorganism with different washing solutions was determined.