Food firmness predicted from combined acoustic and optical data

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  • Published: Oct 30, 2014
  • Author: Steve Down
  • Channels: UV/Vis Spectroscopy / Infrared Spectroscopy / Raman / Atomic / Base Peak / X-ray Spectrometry / Chemometrics & Informatics / MRI Spectroscopy / Proteomics / NMR Knowledge Base

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The firmness of fruit is a key factor in its appeal to consumers who check it out by squeezing but, for producers and suppliers, a more scientific approach is preferred. A longstanding method, the Magness-Taylor procedure, involves the insertion of an instrument into the pulp to measure the resistance but, apart from damaging the fruit, the results are dependent on the force applied by the operator and the part of the fruit that is tested.

More recently, non-destructive methods based on acoustic measurements or infrared spectroscopy have been put forward but they tend to provide variable results. Now a Spanish team claim to have improved the predictability of fruit ripeness by combining acoustic and visible/near-IR data, as they discussed in Journal of the Science of Food and Agriculture.

Using peaches in a proof-of-principle study, the researchers employed a commercial acoustic firmness sensor and measured the visible/NIR spectra, which showed one main peak at 680 nm due to chlorophyll. The acoustic data gave poor correlations with the Magness-Taylor method while the spectroscopic data performed better.

However, a model combining both sets of data performed the best of all using just three parameters: the acoustic signal and the optical signals from 675 and 698 nm. Its simplicity and accuracy mean that firmness can be determined in a non-destructive manner using inexpensive optical devices.

There is no reason to doubt that the technique could be applied to other types of fruit and vegetables and the introduction of an automated system would greatly enhance quality control programs of food producers.


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