A study released by the Center for Food Safety at the University of Arkansas’ Department of Food Science documents that multiple hurdles continue to exist in ensuring reusable plastic containers (RPCs) are clean and lack microbial contamination above safe levels.

The Center for Food Safety conducted a series of four new studies to test sanitizers outlined by the RPC industry. To test sterilization, this study exceeded concentrations by 1,000 times and doubled exposure times deemed safe for consumable food contact by the Environmental Protection Agency (EPA). Results showed that RPCs were still unable to achieve recommended levels for sanitization.

This research is unique in that the study tests RPCs previously used in the distribution stream, according to Dr. Steven Ricke, director of theCenter for Food Safety.

“While we know biofilms cannot be removed with commercial and industrial methods, we wanted to see how many cells of the most common, Salmonella, actually could be removed, if any, by using and exceeding industry and regulatory agency methods, testing four variances such as chemicals and exposure times,” adds Ricke.

After sanitization, the number of Salmonella cells remaining on the individual coupons consistently exceeded the 1,000 organism limit expected on clean RPC surfaces. None of the microbially contaminated RPC coupons treated with the EPA maximum allowable food-contact sanitizer concentrations resulted in residual counts less than 1,000.

In fact, the residual number of Salmonella organism counts ranged from 2,700 to 5.1 million after sanitization, according to the study.

In pre-lab sterilization testing, Ricke also reports the researchers experienced great difficulty removing any remnants of microorganisms on the RPCs. Only RPC coupons that underwent sanitization and disinfection with 70% ethanol after autoclaving in pre-testing were able to pass acceptable levels. Autoclaving, Ricke notes, is only used in laboratories, and the pressurized, steam sterilization vessel is not typically found in commercial settings, nor are disinfectants used with consumable food products.

“While the RPC industry touted 99.5% removal after sanitization, which may sound impressive, the 0.5% actually holds a lot of cells that can cause a lot of trouble,” says Ricke. “It depends on how many cells are there in the first place. Only one cell left behind can multiply, transfer, spoil product or ultimately, make someone sick.”

After inoculation and sanitation at maximum allowable EPA food contact levels, three studies of RPCs taken from the distribution stream recorded only a 2- to 3.48-log reduction out of the 5-log required. Scientists use log reductions, rather than percentages, to represent the actual number of living cells after sanitization. The surviving cells after a log reduction have the potential to transfer to products or surfaces.

To sanitize the RPCs, researchers tested sodium hypochlorite and peracetic acid, both which have been approved for food contact surface sanitization at up to 200 parts per million by the EPA and the U.S. Food Safety and Inspection Service (FSIS), specifying a 5-log reduction in the number of disease-causing microorganisms within 30 seconds of exposure.

“Recent marketing literature from RPC manufacturers notes biofilms are present in the washing process, and that’s a real concern for a safe food supply. Scientists know soap is just soap when fighting harmful bacteria, and using big words or scary sounding chemicals doesn’t change that,” says Ricke. “Retailers, when making packaging decisions with suppliers, need to understand that multi-use packaging can be a potential source for contamination from either coming in contact with tainted food product and returning to the distribution stream, or contaminating new product from packaging, which contains live cells that cannot be removed from cleaning processes.”

SEM technology used by researchers also shows that the process of cleaning multi-use RPCs resulted in compromising surface structures and caused cracks and crevices from repeated and aggressive cleaning of the RPCs that were tested and taken from the distribution stream.

Ricke likened the RPCs appearance in testing to “lunar landscapes” and says biofilms can hide and cause additional hurdles for sanitizers to reach.

“Any promises to remove pathogens or microorganisms from reusable products carrying food items are not based on data,” adds Ricke. “The only guarantee that’s valid from a scientific standpoint is these cells cannot be removed using commercial methods or materials, which is why in the lab during testing, we had to autoclave the RPC coupons taken from the distribution stream to void any microorganisms.”

To eliminate contamination risk, Ricke recommends shippers and retailers choose single-use packaging. While some retailers demand growers and packers use RPCs, others prefer corrugated. Ricke, along with several other food safety experts, encourage retailers to follow the science and avoid risks identified in recent research involving RPCs.