An irrigation method developed by food scientist Robert Beelman has resulted in mushrooms that are safer, fresher, and more nutritious

Some Penn State food research is aimed at enhancing an agricultural product's freshness or processing characteristics. Food scientist Robert Beelman studies cultivation and postharvest practices that can lead to better mushrooms in the supermarket. For instance, he and plant pathologists at Penn State have developed an irrigation method that uses calcium chloride to improve fresh and canned mushrooms. "We found that mushrooms irrigated with water containing calcium chloride are whiter, have fewer potentially harmful bacteria, and have up to twice the shelf life of mushrooms irrigated with tap water," says Beelman.

Calcium chloride is an inexpensive additive often used in canning fruits and vegetables because it keeps them firm. Beelman found that when added to irrigation water in amounts as small as 0.3 percent, the substance can reduce bacteria populations at harvest by up to 50 percent. "Water on the surface of mushroom caps can promote bacterial growth," he explains. "Calcium chloride may cause surface moisture to dry faster, improving color and inhibiting the growth of pathogens and bacterial blotch, which causes dark spots to develop on the cap. This helps growers by reducing the number of mushrooms that are downgraded and sold to canners at a much lower price. The process also increases the calcium content in the mushrooms, which has potential health benefits for consumers."

Irrigating with calcium chloride also can benefit mushroom processors. "When mushrooms are cooked or canned, they tend to shrink by up to 40 percent of their size and weight," says Beelman. "Treating mushrooms with calcium chloride can reduce shrinkage by 1 to 2 percent. That may not sound like much, but every 1 percent reduction in shrinkage is worth at least $1 million to the mushroom canning industry."

Beelman also studies postharvest handling and packaging technology that may improve mushroom quality. "Before fresh mushrooms are packaged, they are washed, and the excess moisture can promote bacterial growth and spoilage," Beelman says. "Sulfites often are used to retard spoilage, but some people are allergic to them. We're investigating novel approaches to eliminate the need for sulfites. In addition, we're looking at modified-atmosphere packaging. Mushrooms keep better if they are stored in an atmosphere of low oxygen, high carbon dioxide, and optimum humidity. If humidity is too low, you get browning and shriveling; if it's too high, you get microbial growth. One of my food science colleagues has developed a practical method for maintaining ideal conditions in conventional packaging, which promises to keep mushrooms safer and fresher longer."