Postharvest washes tackle residue, quality issues

Food safety remains top-of-mind for all involved in the produce industry. One of the ways to minimize risks associated with microbial pathogens is for vegetables and fruits that have noticeable soil or organic matter residues on their surface to be meticulously washed before sale or processing.

Chlorine is a very common disinfectant that can be added to transport flumes or to produce cooling or wash water. Liquid sodium hypochlorite is typically used, with the pH of the water maintained between 6.5 and 7.5 to optimize effectiveness.

Keith Warriner, professor in the Department of Food Science at Canada’s University of Guelph said the role of the postharvest wash has changed over the last two years.

“We have gone away from assuming that pathogens are removed from produce by washing. What the aim is now is to minimize cross-contamination,” he said. “To this end, work is being performed to identify the level of free sanitizer required to be in the wash to reduce cross-contamination (i.e. pathogen inactivation). Most work has been performed with hypochlorite, given it is the main sanitizer used in wash tanks.”

The problem with this method is that chlorine becomes sequestered by organic material. Therefore, it becomes a bit like trying to hit a moving target in terms of maintaining chlorine as it is constantly being neutralized.

Water with additives, such as chlorine or a number of new products, is a key component in reducing food safety risks, supporting product quality and eliminating food waste.
Water with additives, such as chlorine or a number of new products, is a key component in reducing food safety risks, supporting product quality and eliminating food waste.

“Our solution to the problem is to use wastewater treatments to maintain organic content of water to preserve the chlorine concentration,” Warriner said. “Another approach is to use water-free decontamination methods based on UV peroxide or ozone gas.

Erika Staton, business development analyst at SmartWash Solutions, Salinas, California, said fresh, ready-to-eat salads and vegetables must be washed to remove dirt and debris from field and harvest activities, as well as fines (very small particles) and latexes released during the cutting and preparation process.

“This is required to preserve freshness and deliver fresh, wholesome products to the consumer. However, the water used to wash the produce must be maintained to the highest hygiene levels at all times,” she said. “Waterborne cross- contamination can be one of the most significant influences on the size of an outbreak. Water can be the primary vector for the spread of microorganisms, causing entire production runs or lots to become contaminated and likely increasing the scope of an outbreak.”

However, if the wash process is properly managed and the right mitigations are in place, then a processor can prevent cross-contamination and reduce the presence of microbes during the postharvest wash.

Warriner said that postharvest washes must be done to remove soils from produce and enable transport of fruit or vegetables through the process (i.e. flume water).

“Previously, it was thought to remove pathogens and pesticides, although the washing process more likely spreads contamination across batches of produce,” he said. “There is the thought that postharvest washing actually increases food safety risks through spreading contamination pathogens and pesticides. My thoughts are that washing reduces pathogens and pesticides, so (it) does contribute to reducing the risk, although (it is) by no means a magic bullet.”

Effect on food safety

Produce is typically washed in one or more stages with rinses either in between or at the end of the washing. The produce is tumbled in the wash water, helping to remove debris from the field and ensure complete submersion of the produce. As the produce passes through the wash system, it is exposed to one or more hurdles including antimicrobials and wash aids that prevent the survival of the microbial contamination in the water.

“Since there is not a traditional kill step with fresh- cut produce, and quality is to be maintained, the wash step must do no harm,” Staton said. “In the presence of harmful bacteria, water is a well-established vector for their movement from leaf to leaf. However, control of the wash water chemistry is key to ensuring that this will not happen. Poorly controlled wash water can lead to cross-contamination, taking a small problem and making it much larger.”

Does it help with food waste?

According to Phil Tocco, a food safety educator with Michigan State University Extension, washing fruits and vegetables straight from the field in a properly equipped dunk tank or hydrocooler can be of great benefit, not only improving its safety to the consumer but extending the shelf life of the produce.

Many facilities expose themselves to production losses when the postharvest wash is not managed effectively. For example, if a product is washed below the facility’s critical control point, that product should be disposed of.

“Studies have shown that once cross-contamination has occurred in wash systems, it is almost impossible to correct, which is why it is extremely important to properly wash the product the first time, both for food safety and operational costs,” he said. “Additionally, proper wash techniques may extend the shelf life of produce by removing harmful mildews and molds, making the product more appealing to the consumer for a longer period of time.”

Bill Diederich, senior executive vice president of agribusiness for BiOWiSH Fruit and Vegetable Wash, notes that if you look at the issue on a global basis, the answer is different in each region, but a global answer to the importance of postharvest washing concerns fruit security issues as populations continue to grow and farming acres continue to shrink.

Postharvest washing is important, he notes, to increase shelf-life, resolve latex issues, improve fruit quality, improve and conserve water, reduce chemical products and electricity usage and provide a savings in man-hours used for cleaning.

“We as fruit producers are doing all we can to continue to increase the amount of fruit production on a per-area basis, but projections put us well short of where we need to be for future fruit demand,” he said. “When you look at what’s happening in Africa and other places and the amount of food waste due to food transportation, it’s because of a lack of refrigeration. Washing dramatically reduces fruit spoilage.”

Warriner notes that by washing, the spoilage microbes should be removed.

“However, it is more likely that washing intact produce results in condensation on the surface of produce and hence spoils more quickly,” he said. “Rather than washing, it is temperature and modified atmosphere that are responsible to extending the shelf life – hence reduced food waste.”

Of note

The biggest buzz in the industry right now is the new Food Safety Modernization Act (FSMA) regulations, and how to ensure compliance with the new requirements.

“FSMA is very focused on ensuring that potential hazards are identified and systems are instilled to control them,” Staton said. “This includes monitoring, control and documentation, disinfectant controls and real-time wash water data.”

— Keith Loria, contributing writer

Be sure to check out our other specialty agriculture brands

Organic Grower