The University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) Indian River Research and Education Center’s (IRREC) Postharvest Technology lab, led by Mark Ritenour, is researching how to reduce decay in strawberries and blueberries and improve their quality during the postharvest process.

This project is a continuation of other research they have worked on that looked at essential oils and antimicrobial gases to help control decay and bacteria after harvesting.

Ritenour said the goal is to develop these gases and oils so they could be used commercially.

“We wanted to come up with a commercial way to treat strawberries and blueberries and also something we could leverage at different times of the season,” Ritenour said.

The ultimate goal of the lab’s project is to help more strawberries and blueberries have less decay when in clamshell containers and last longer in the refrigerator when consumers take them home.

When studying the effectiveness of essential oils, they found two, carvacrol and thymol, to be the most effective at reducing decay and bacteria.

However, both of these oils can cause odors, which could potentially limit their commercial appeal.

Ritenour’s lab found two antimicrobial gases that were effective with the fruit – chlorine dioxide and sulfur dioxide.

They found chlorine dioxide was able to reduce E. coli in strawberries and blueberries. He said they worked with an industry partner to develop sachet pads that release the gas directly into fruit packaging.

“You get a chlorine dioxide gas that’s slowly released, or different release timings, a faster release or slower release,” he said. “We just place a pad on top of each flat of strawberries or blueberries and then ship it away.”

Sulfur dioxide is typically used for grapes and is now able to be used for blueberries. He said strawberries are currently being evaluated to see if the gas would be effective. “They’re working on a label for strawberries, so we decided to start testing those, as well,” he continued.

Fruit quality is described as multi-dimensional and it includes visual quality, internal quality and retention and shelf life. When evaluating the fruit, the lab looks at the amount of decay and how much tissue damage the fruit had.

They also look at browning, sugar and acid levels, as well as firmness, which they particularly look for in blueberries.

“The main thing we’re looking at right now is decay and injury,” he said. “We also look at browning of the calyx or necrotic areas, because that tells us we’re getting too high of a concentration. We have not observed any changes in chemical composition, including sugars or acids.”

The biggest hurdle they’ve come across is variability. This includes differences between batches, growing locations, and weather conditions. It can also involve dominant decay organisms that appear depending on where and how the fruit was grown.

Some decay issues originate before fruit is harvested, meaning that postharvest treatments can only extend, not restore, fruit quality.

“Once the product is harvested, its maximum quality is already determined,” he said.

Ritenour said his lab is finding the treatments are working. They found that moderate concentrations of chlorine dioxide are just as effective as higher ones, which is beneficial for safety and cost.

“Now the challenge is working out the kinks and finding the best commercial way to apply it,” he said.

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