OREGON STATE UNIVERSITY

Edible coatings slow rot, increase shelf life in pre-washed fresh blueberries

10/05/2010

CORVALLIS, Ore. – Researchers at Oregon State University have developed new techniques for handling fresh blueberries – including a method of pre-washing them for market and applying an edible coating – that may extend the shelf life of this popular Oregon crop and open up new markets for its sale.

 Edible coatings are being used by scientists in OSU’s College of Agricultural Science to extend quality and prolong storage of two varieties of blueberry, Duke and Elliott. The coatings can also slow decay and water-loss after the fruit is washed.

In two years of trials, fresh blueberries were first washed with chlorinated water then dipped in one of five different edible coatings before being placed in storage containers. The berries were evaluated for quality after 15 days. Results from the study suggest that this technique could be used to develop ready-to-eat blueberries with no reduction in shelf life.

Findings will be published in the journal Postharvest Biology and Technology, which is in press.

Fresh untreated, unwashed blueberries have a typical shelf life of one to eight weeks depending on several factors, including variety, ripeness at harvest, method of harvest, presence of disease, and storage conditions. Washing the fruit prior to packing and storing can increase the rate at which the fruit deteriorates, said Yanyun Zhao, a professor in OSU’s Department of Food Science and Technology.

“The use of edible coatings can increase the market value of the fruit by allowing the establishment of pre-washed, ready-to-eat fresh fruit as a convenience for consumers,” said Zhao, one of the researchers on the project.

The coatings used in the study were: Semperfresh, acid-soluble chitosan, water-soluble chitosan, calcium caseinate and sodium alginate. Semperfresh is a sucrose ester; chitosan is a derivative of chitin – a natural substance often found in the exoskeletons of insects and crustaceans, and alginate is a polysaccharide commonly found in the cell walls of brown algae.

 In other berries, the use of edible coatings has been found to partially control internal gas exchanges within the fruit, delaying fruit post-harvest respiration and to serve as a barrier to water vapor, effectively slowing moisture loss and dehydration.

“Use of appropriate coatings and application methods delays fruit dehydration or wrinkling in washed berries,” said Bernadine Strik, a co-author on the study and a professor in OSU’s Department of Horticulture. “This opens up a whole new possible market sector for pre-washed blueberry fruit.  Considering the health benefits of blueberries, this is a positive step for consumers and the industry.”

There are more than 300 blueberry growers in Oregon, and production regularly tops more than 40 million pounds, about 30 to 50 percent of which are sold and consumed as fresh berries. Acreage devoted to the crop has increased four-fold in the last decade, according to the Oregon Agricultural Statistics Service, with farm sales totaling more than $37 million last year.