Using the Streif Index as a final harvest window for controlled-atmosphere storage of apples

A final harvest window (FHW), expressed as Streif Index coefficients [firmness/(percentage soluble solids concentration x starch index)], was developed for identifying maximum fruit quality for strains of 'McIntosh', 'Cortland', and 'Jonagold' apples (Malus x domestica Borkh.) following 8 months of controlled-atmosphere (CA) storage. The Streif Index was calculated during nine preharvest (twice per meek) intervals and four weekly harvests over three seasons. The relationship between Streif Index (dependent variable) and day of year (independent variable) of the preharvest and harvest samples was then derived by negative first-order linear regression equations that had parameter estimate (b(1)) probability values less than or equal to 0.0001 for all of the strains. Apples from the four harvest periods were stored in standard CA storage for 8 months and then subjected to a 7-day shelf-life test at 0 degrees C followed by 5 days at 20 degrees C. Poststorage quality data were categorized and combined to produce an overall fruit quality rating scale. For each strain, the final harvest (i.e., day of year) was identified as that which directly preceded at least a 10% drop in the poststorage fruit quality rating compared with the first harvest rating. The FHW, expressed as Streif Index coefficients via the regression of Streif Index (Y) on day of year (X), was then calculated as the 3-year final harvest mean with the upper and lower window limits being determined by the standard deviation of the mean. The lower to upper FHW boundaries ranged from 4.18 to 5.34, 4.12 to 5.46, 4.51 to 5.68, 5.23 to 599, and 1.38 to 2.34 for Redmax, Marshall and Summerland 'McIntosh', Redcort 'Cortland' and Wilmuta 'Jonagold', respectively. The practical utility of the Streif Index method lies in the ease with which apple fruit maturity at harvest can be evaluated for its suitability for long-term CA storage.