A new approach to controlling Listeria in postharvest fruit and vegetable production

The recent update to Regulation (EC) No 2073/2005 on microbiological criteria for foodstuffs reinforces the need to demonstrate that ready-to-eat (RTE) foods maintain their microbiological safety throughout their commercial shelf life. This new regulatory framework poses a challenge for the fruit and vegetable sector, particularly for products consumed without prior heat treatment. In minimally processed fruits and vegetables, such as washed salads, cut vegetables, fresh-cut fruit, and packaged ready-to-eat products, microbiological safety is a key element of postharvest technology. In this context, the control of Listeria monocytogenes cannot rely solely on end-product testing but must instead be addressed through a preventive and integrated strategy encompassing the entire processing chain. This strategy should consider factors such as the microbiological quality of raw materials, wash water management, hygienic design of equipment and facilities, cleaning and disinfection procedures, separation of clean and dirty processing areas, environmental monitoring, and strict maintenance of the cold chain.

A pathogen adapted to processing environments

L. monocytogenes is one of the major hazards associated with ready-to-eat foods due to three characteristics that make it particularly difficult to control: its remarkable ability to adapt to environmental conditions, its capacity to persist for long periods within processing facilities, and its potential to grow at low temperatures. Unlike many other foodborne pathogens, Listeria can multiply even at temperatures close to 0°C. Therefore, although refrigeration is essential for preserving the quality and safety of fresh produce, it alone cannot guarantee control of the microorganism.

Within fruit and vegetable processing lines, the highest-risk areas are typically drains, conveyor belts, cutting equipment, sorting tables, and other wet or hard-to-clean locations. Crevices, joints, and poorly designed surfaces may become persistent niches where the microorganism finds favorable conditions for survival. Furthermore, Listeria can persist even in facilities with high sanitation standards because of its ability to form biofilms—microbial communities attached to surfaces and protected by an extracellular matrix that reduces the effectiveness of disinfectants. Biofilms often develop in hidden or difficult-to-access areas, limiting the efficiency of cleaning operations. As a result, certain sites within the facility may act as reservoirs from which the bacteria are intermittently released, leading to recurring episodes of recontamination.

What changes under the new European regulation?

The main change introduced by Regulation (EU) 2024/2895, which will enter into force on 1 July 2026, is conceptual: it is no longer sufficient to demonstrate that a product is safe at the time of manufacture. Food business operators must now be able to demonstrate that the product will remain safe throughout its entire commercial shelf life.

In practice, this means that operators must provide scientific evidence and technical documentation demonstrating that L. monocytogenes will not exceed the limit of 100 CFU/g at any point during the product's shelf life. If this justification cannot be provided to the competent authority, the stricter criterion of "absence of L. monocytogenes in 25 g" will automatically apply before the food leaves the manufacturer's direct control.

This regulatory change reinforces the need to adopt preventive strategies, as failure to comply with microbiological criteria may result in product recalls, notifications to competent authorities, financial losses, and significant damage to consumer confidence and brand reputation.

For the fruit and vegetable sector, the new regulation requires evaluating each product individually, since not all food matrices behave in the same way with respect to Listeria growth. Factors such as product type, packaging conditions, storage temperature, and assigned shelf life may significantly influence the behavior of the microorganism. In this context, environmental monitoring and shelf-life studies, including challenge tests, become essential.

Controlling the environment to protect the product: the importance of environmental monitoring

Adapting to the new regulatory framework requires implementing a dedicated environmental monitoring program for L. monocytogenes, aimed at identifying where the microorganism may occur, where it can persist, and how it may be transferred to the product.

Such a program should define the areas and surfaces to be sampled, including both food-contact surfaces and adjacent or difficult-to-access areas. It should also establish sampling frequencies according to risk level, determine appropriate sampling times—before, during, and after processing operations, both while the production line is operating and after cleaning and disinfection—and include clear criteria for interpreting results and implementing corrective actions when necessary.

The monitoring program should also rely on suitable detection methods with sufficient sensitivity and turnaround times compatible with plant decision-making. Improvements in analytical techniques, including rapid methods, confirmatory tests, and strain typing when appropriate, can help distinguish between sporadic contamination events and persistent strains, providing a better understanding of the microorganism's behavior within the processing environment.

Shelf-life studies and challenge tests: demonstrating safety until the end

Shelf-life studies and challenge tests are among the cornerstones of the new regulatory framework. For fresh produce, shelf life should no longer be determined solely on the basis of visual, sensory, or commercial criteria but should instead be supported by microbiological evidence demonstrating that L. monocytogenes will remain below regulatory limits throughout the product's marketed shelf life.

These studies determine whether the assigned shelf life is compatible with microbiological safety under realistic manufacturing, distribution, and consumption conditions. They also help identify factors that may promote Listeria growth, validate the effectiveness of preservation strategies, and assess the impact of changes in processing, packaging, or storage conditions.

In other words, shelf-life studies and challenge tests enable evidence-based decision-making, allowing manufacturers to establish realistic shelf lives while reducing the risk of product recalls and food safety incidents.

Generating this scientific evidence often requires collaboration with research centers, universities, technology-based companies, and accredited laboratories capable of designing and conducting shelf-life studies and challenge tests according to protocols recognized by the European Food Safety Authority (EFSA).

From regulatory compliance to innovation: new preservation strategies

Preventing L. monocytogenes in ready-to-eat foods requires a multifactorial approach. No single intervention can guarantee control of the microorganism; success depends on combining multiple preservation hurdles tailored to the characteristics of each food matrix. This concept, known as hurdle technology, simultaneously targets different factors influencing microbial growth, including storage temperature, pH, water activity, initial microbial load, packaging conditions, and the accompanying microbiota.

Among the available strategies are optimization of washing treatments, improvements in processing environment sanitation systems, and the development of new preservation solutions based on natural ingredients and additives. In addition, the incorporation of advanced technologies such as cold fogging is strengthening environmental control of the pathogen through approaches aligned with clean-label trends.

In recent years, research into plant extracts and their bioactive compounds, bioprotective cultures, and other biopreservatives has opened new opportunities to enhance microbiological safety without compromising sensory quality or consumer acceptance. Public-private R&D&I initiatives are accelerating the identification and implementation of innovative preservation strategies for fourth- and fifth-range foods.

One example is the European InnoSol4Med project (PRI-20220002), co-funded by the Centre for the Development of Industrial Technology (CDTI) under the PRIMA Initiative, involving the Spanish National Research Council (CSIC), the biotechnology company DOMCA, specialized in preservation solutions for the food industry, and other international partners. The project explores the potential of plant extracts and bioactive compounds from the Mediterranean diet to develop sustainable preservation strategies capable of controlling Listeria, extending shelf life, and reducing dependence on conventional preservatives in ready-to-eat foods. Its main research areas include optimizing critical processing stages, combining different technological hurdles, and validating clean-label preservation strategies.

Similarly, DOMCA, together with the Universities of Jaén and Granada, is participating in the CENTINELA project, funded by Andalucía TRADE, which focuses on developing biopreservatives to improve the microbiological safety of ready-to-eat foods. Although the project's initial application extends beyond the fruit and vegetable sector, the knowledge and solutions generated are highly transferable, contributing to the development of innovative preservation strategies for minimally processed fresh produce.

Adapting to the new regulatory framework represents an opportunity to drive innovation and accelerate the adoption of more effective, sustainable preservation solutions aligned with consumer expectations. The combination and validation of these strategies not only demonstrate microbiological safety throughout the product's shelf life but also optimize processes, reduce the risk of food safety incidents, and strengthen the competitiveness of the fruit and vegetable sector.

The authors of this article are Alberto Baños¹, Abdelkader Boutine², Andrea Navarro², and Ana Falcón-Piñeiro².

¹ Spanish National Research Council (CSIC). Estación Experimental del Zaidín (EEZ-CSIC)

² Department of Microbiology and Biotechnology, DOMCA SAU, Granada, Spain.

More information at Domca.