Non-destructive detection of pits in dried plums

An economical, non-destructive device was constructed to detect pits in dried plums (prunes). The device compresses the product between a roller and a force transducer, which detects the higher force generated when a pit is present. Two methods of classifying fruit were developed, one based on the maximum magnitude of the compression force and the other on analysis of the frequency spectra of the force transducer signal during compression. The accuracy of the former was 98.6% for pitted fruit and 69.4% for fruit with pits, versus 99.1% and 75.3% for the latter. The frequency spectra classification method was more accurate, but more complex and costly to implement. The requirement to restrict the compression of the fruit to be non-destructive precludes the possibility to detect small pit fragments using this method. However, the low cost of materials for the device make it a potential method to supplement other technology currently in use to reduce the pit count in the final product.