Public Release: 

Penn State Scientist Heats Up Research On Package Humidity

Penn State

University Park, Pa. -- When it comes to improving the quality and shelf life of packaged fresh mushrooms, it's not the heat, it's the humidity, says a food scientist in Penn State's College of Agricultural Sciences.

The shelf life of the common button mushroom is limited to three to five days on a store shelf, says Dr. Ramaswamy Anantheswaran, associate professor of food science. Typically, mushrooms are packaged in containers covered by plastic film with air holes.

The researcher has recently completed research on two mushroom packaging methods. One project focused on modifying the oxygen concentration within individual wrapped packages, and the other sought ways to modify the humidity within single wrapped packages.

Anantheswaran's idea to control oxygen content within mushroom packages evolved from research on controlled atmosphere storage, in which precisely controlled gases are used to keep produce from ripening or spoiling.

"Controlled atmosphere storage has been in use since the 1930s," Anantheswaran says. "Obviously you cannot precisely control the atmosphere within a small package. But if we can maintain the atmosphere inside the package within a certain range of factors, we can improve the quality of mushrooms as well as other produce."

In the laboratory, Anantheswaran found that controlling oxygen within a package worked well. Unfortunately, the package had to be maintained at a relatively constant temperature, a factor that cannot be guaranteed on the mushrooms' trip from processor to market.

Undeterred by the havoc heat had brought to his modified atmosphere work, the Penn State scientist turned to humidity. "When mushrooms are harvested, more than 90 percent of their weight is water," he explains. "Mushrooms also don't have a skin like other types of produce, and give off much more water vapor."

This vapor can collect within the package and cause discoloration and growth of bacteria. Humidity within produce packaging is a common problem that can affect the appearance and safety of the food product. Anantheswaran says that excess water causes button mushrooms to brown or yellow in blotches that are unsightly to consumers. Excess humidity also fosters the growth of harmful microorganisms.

"Although mushroom packages are vented with air holes, it is difficult to remove moisture once it forms," Anantheswaran points out.

He is currently testing several commercially available moisture adsorbers to regulate moisture within food packaging. Adsorption occurs when thin layers of molecules adhere to the surface of solids or liquids, much like odors are adsorbed by baking soda.

"Modifying the humidity in mushroom packages is particularly challenging because mushrooms respire at a high rate when harvested and gradually level off," says Anantheswaran. "Also, the adsorbing agent cannot totally eliminate humidity, because the produce would then dry out."

Adsorbing agents such as salt crystals and sorbitol, a chemical adsorbent, were tested in different amounts. Anantheswaran and other researchers tested a variety of plastic films for water vapor permeability as well. "The aim of the research was to keep the moisture production of the mushrooms slightly higher than the combined rates of moisture absorption by the absorbing agent and moisture loss through the package film," Anantheswaran says.

According to Anantheswaran, the modified humidity packaging improved the maturity of the mushrooms, effectively increasing the shelf life for the product. Anantheswaran is currently looking into a package design that would incorporate moisture adsorbers into the structure of the package.

"This modified humidity packaging can be used with any type of produce," Anantheswaran says. "Why stop with mushrooms? Other types of produce emit varying amounts of moisture, and the amount of absorbing agent can be adapted to maintain the humidity within a range of values."


EDITORS: Dr. Ramaswamy Anantheswaran is at (814) 865-3004.

John Wall (814) 863-2719 office
Eston Martz (814) 863-3587 office

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