Edible coatings help manage fruit dehydration, respiration.

Hardy kiwifruit are quickly gaining popularity due to their flavor and high nutritional value. The fruit usually are not picked vine-ripe, but green-ripe for easy shipment. It's possible to use edible coatings to control the fruit's dehydration and respiration during postharvest storage, thus extending the product's shelf life.

There has been little research on how aroma evolves in hardy kiwifruit during the postharvest storage period. So, scientists at Oregon State University developed a rapid headspace solid-phase microextraction-gas chromatography (SPME-GC) technique that enabled them to quantify volatile compounds in hardy kiwifruit and investigate the effect of edible coatings on those compounds. Their research indicates that positive aroma compounds can develop during storage, and that edible coatings may not change the postharvest physiology of hardy kiwifruit.

The researchers coated under-ripened hardy kiwifruit (~9 brix) with Semperfresh, a commercial edible coating material. Both the control and coated samples were stored at 2 C and 88% relative humidity, without light, for up to 10 weeks. Samples were taken after weeks 5, 6, 7, 8, 9 and 10 and were transferred to a freezer at -23 C until they were analyzed.

The scientists blended four kiwifruit under liquid nitrogen. An 8-g portion of the powder was mixed with an internal standard solution, sodium chloride, calcium chloride and water. The researchers used headspace SPME-GC to analyze the volatiles. This approach can be used reliably to analyze volatile compounds in hardy kiwifruit with a correlation coefficiency of greater than 0.99 for most compounds. During storage, the content of esters, terpinene-4-ol and terpineol increased, while levels of aldehydes, myrcene and terpinolene decreased. Both the coated and the control samples followed the same trend.

The kiwifruit is from the cultivar group of the woody vine Actinidia deliciosa and hybrids between this and other species in the genus Actinidia. The fruit gets its name from a marketing strategy, when it was named after the kiwi, the national bird of New Zealand, where the fruit was first commercially popularized in the late 1950s.

Further information. Michael Qian, Department of Food Science and Technology, 244A Wiegand Hall, Oregon State University, Corvallis, OR 97331; phone: 541-737-9114; fax: 541-737-1877; email: michael.qian@oregonstate.edu.