Non-destructive harvest measurement can predict rate of softening of fast- and slow-melting peaches

Peaches are harvested selectively based on size and color, both peel background color and extent of blush. The background color of the fruit changes from green to yellow as chlorophyll disappears, and in many cultivars with red coloration this is hard to determine. A portable instrument that measures I_AD (the index of absorbance difference between 670 and 720 nm) was used for monitoring the progression of ripening in two peach cultivars. I_AD was measured at harvest in 'Oded' (an early season, fast melting flesh peach) and 'September Snow' (a late season, slow melting flesh peach). After harvest the fruits were divided into comparable lots and held at 20°C. The I_AD and firmness were measured daily on a different lot. Two analytical methods were applied to the data. In the first, firmness decrease during shelf life was analyzed by nonlinear regression, using the I_AD measured at harvest to determine the maturity of the fruit, and to estimate the biological shift factor (BSF) which is related to the biological age of fruit. In the second, a prediction equation for firmness was developed as a function of initial I_AD, giving a table of the probability of a fruit to be less than 20 N on each day of shelf life. In both these methods the measurement of I_AD at harvest could be used to separate fruit into different groups according to their rate of softening, and, therefore, potential shelf life.