Comparison of standard 11-mm penetrometer plungers against 8-mm plungers to establish the optimum harvest maturity of late season nectarines using flesh firmness as indices

摘要

The primary aim of this study was to establish if 8-mm diameter penetrometer plungers can provide a versatile alternative to standard 11 -mm plungers, to accurately measure the flesh firmness of nectarines intended for sea export, as well as to identify changes to improve existing maturity standards where appropriate. Testing was done over two seasons on Alpine, Summer Fire, August Red and September Bright nectarines, while Regal Pearl, Sunburst, Summer Sweet and Top Pearl were evaluated over one season. The early season cultivars - Alpine and Sunburst - were included as references. Each population of nectarines was harvested at three maturities, approximately one week apart, commencing one week before the start of the commercial optimum maturity window. Harvest maturity was determined with a focus on comparing efficacy of flesh firmness measured, using penetrometers fitted with standard 11 -mm diameter plungers against 8-mm plungers. The quality of fruit sampled at each harvest was evaluated afterfour weeks at -0.5°C, followed by a shelf life of 5 days at 10°C. This study emphasised the importance of flesh firmness as maturity indices for nectarines. The 11-mm and 8-mm plungers both indicated separation of maturities acrossharvest dates. The benefit of the 8-mm plunger was that it was suitable for use on firmer nectarines that typically crack with the thicker plunger. This can be of great value for some new late-season nectarine cultivars, where it seems that harvest may need to commence with the maximum standards higher than the 11.3 kg flesh firmness traditionally measured with the 11 -mm plunger. Use of the 8-mm plunger is also likely to simplify the quality control process since it's widely used by international clients. A division factor of 1.8 can be used to convert existing standards from 11-mm to 8-mm. Maturity standard changes are suggested for Summer Fire and August Red, namely: flesh firmness between 8.0 and 4.5 kg with an 8-mm plunger (13.6 to 8.0 kg with an11 -mm plunger), irrespective of total soluble solids levels. This implies an earlier optimum harvest window. Standards for Alpine and September Bright remain unchanged. Additional testing to verify the optimum harvest maturity windows is recommended forRegal Pearl, Sunburst, Summersweet and Top Pearl, as well as all other new cultivars. Based on this research, Hortgro has recommended to the Department of Forestry and Fisheries, that a Regulation change be made to specify that the 8-mm plunger be usedto determine the flesh firmness at harvest for certain nectarine cultivars. Consequently there is an industry wide dispensation to use the 8-mm plunger on the cultivars listed in Table 1. All the existing riders remain applicable.