Measuring blueberry firmness and modelling quality changes for delays in cooling using the FirmTech II
Tetteh, Mark Kofi
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Blueberry firmness values (g/mm) measured by a FirmTech II depended on calyx orientation (up, down, or horizontal). A 3-D plot showed large changes in firmness resulting from different minimum and maximum settings. A recommended standard is to use only the first measurement with the calyx horizontal at 50-g minimum and 150 g maximum force. Applications of Hertz contact equations (ASAE standard S368.4) showed a need for including the 3/2th power on the deformation value in the FirmTech II output and the radius of the fruit. Firmness and mass changes for different cooling delays and at different temperatures were modeled. Predictive curves were generated and plotted against actual data. Plots of predicted versus observed values showed that the models generated predicted mass losses better than firmness losses of the blueberries. Immediate cooling was less critical at 21.... C and 27 °C than at 32 °C.