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'Tooth' tool tests apples

Machine lets WSU test more fruit for crispness, firmness


Capital Press

WENATCHEE, Wash. -- The Washington State University Apple Breeding Program plans to rely more on a new machine measuring apple firmness and crispness as it seeks to improve those qualities in new varieties.

The machine, called an MDT-1, was developed by Mohr and Associates of Richland, Wash., and will enable researchers to evaluate firmness and crispness in greater volumes of fruit faster than they can with trained, human taste-testers.

Researchers at the WSU Apple Breeding Program in Wenatchee, led by molecular biologist Kate Evans, found a significant correlation between the MDT-1's crispness measurements and crispness ratings by trained people, according to Evans' report in the December 2010 issue of HortTechnology.

"Think of the MDT-1's plunger as a mechanical tooth," said Brandt Mohr, Mohr's chief technologist.

The MDT-1 measures the energy released by the crunch of the apple as the plunger advances in a way that is repeatable and operator-independent, Mohr said.

"Fruit firmness alone is not adequate because a firm apple is not necessarily a crisp apple," he said.

The MDT-1 is a next-generation replacement of the hand-operated Magness-Taylor penetrometer the industry has relied on for decades to measure firmness. It is also manufactured by Mohr and Associates.

The company is planning to release a new MDT-2 in the second quarter of 2011. Like the MDT-1, the computerized penetrometer will be able to measure numerous quality parameters in high volumes of fruit and other agricultural commodities.

Features include automated reports, barcode scanner integration and custom fixtures for general materials testing.

Evans said she tested two MDT-1s in 2009 and 2010. She said she plans to continue using the instruments to evaluate a greater volume of fruit than she could otherwise.

"Human taste testing is the most informative. You can't get away from that, but it's labor-intensive and subjective," Evans said. "The MDT-1 is better than the standard penetrometer, but taste testing is the best ultimately. You have the mix of everything, not just firmness and crispness but the whole eating experience."

Trained people evaluate firmness, crispness, mealiness, juiciness, sweetness, acidity and astringency, a sort of bitterness, she said.

"People will always be best but you can't run 1,000 samples through people the same way you can through an MDT. It helps winnow things down," Evans said.

WSU began sensory taste testing of apple breeding selections in 2007 or 2008 and in February plans to release its first evaluations of five commercial varieties -- Fuji, Gala, Honeycrisp, Cripps Pink and Granny Smith, Evans said.


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