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Maximum maturity indices for different packinghouse conditions based on cultivar critical bruising thresholds and bruising potentials were developed for stone fruit cultivars. The critical bruising thresholds, based on fruit firmness, and the bruising probabilities varied among stone fruit cultivars. In general, plums tolerated more physical abuse than yellow-fl esh peach, nectarine, and white-flesh peach cultivars. Impact location on the fruit was an important factor in the determination of critical bruising thresholds. Potential sources of bruising damage during fruit packing were located using an accelerometer (IS-100). A survey of different packinghouses revealed that bruising potentials varied from 21 to 206 G. Bruising potential was reduced by adding padding material to the packinglines, minimizing height differences at transfer points, synchronizing timing between components, and reducing the operating speed. Bruising probabilities for the most-susceptible California-grown cultivars at different velocities and Gs have been developed. Development of a practical sampling protocol to determine fruit firmness during maturation was studied.
The use of ultraviolet fluorescence to identify freeze-damaged navel oranges (Citrus sinensis) was evaluated using fruit harvested following a natural freeze that occurred in California in Jan. 2007. Navel oranges were harvested after the freeze from 14 sites that were previously determined to have a slight to moderate amount of freeze damage. The fruit were evaluated for the presence of small yellow spots characteristic of freeze damage that fluoresce when viewed under a ultraviolet-A (365 nm) source and were then cut and rated using a method currently used by the California Department of Food and Agriculture (CDFA) to determine the presence of internal freeze damage. The percentage of freeze-damaged fruit in each lot as determined by the CDFA method ranged from 0% to 89%. The accuracy of classifying fruit as freeze damaged in each lot by peel fluorescence averaged 44%, with the fruit lots containing the greatest amount of freeze damage having the highest classification percentages. False-positives occurred at a lower rate than false-negatives among the lots. Although some fading was evident, the fluorescence persisted and was readily visible for at least 9 weeks after the freeze event. Removal of fruit with ultraviolet peel fluorescence was ineffective in reducing the percentage of damaged fruit within the examined lots. In the second part of the test, eighteen lots of potentially freeze-damaged fruit were obtained from a packing house, immediately evaluated for freeze damage using ultraviolet light, and then after 4 weeks of storage, were evaluated again using the CDFA method. Fruit that had a slight to moderate degree of freeze damage were tasted and evaluated for sensory characteristics. Both methods of freeze damage detection were poorly related to the sensory characteristics.