DEVELOPMENT AND VALIDATION OF THE MASS LOSS SEGREGATION SYSTEM FOR APPLES

There is a high level of variability in development of shrivel and levels of weight loss between apples (Malus domestica Borkh.) from different growers in storage. This variability derives from large variation in skin water vapour permeance (mol.s.m.Pa) within populations of fruit. Relationships found between shrivel, weight loss, and water vapour permeance for grower batches were used to develop a prediction system for the New Zealand Pipfruit industry that enables the identification of batches of fruit at risk of developing shrivel in storage. The mass loss segregation system measures water vapour permeance on random samples of fruit from batches of fruit from growers. Predictions of the risk of shrivel developing in batches of fruit during storage were made on 289 and 116 batches of ‘Braeburn’ and ‘Pacific Rose’ apples grown in the Hastings region. The mass loss segregation system was validated in 2002 using 500 fruit samples from 49 and 35 batches of ‘Braeburn’ and ‘Pacific Rose’ apples taken at harvest, respectively, and stored under commercial conditions for 6 months. Fruit were removed in September 2002 and incidence of shrivel was assessed. The models predicted the groupings of shrivel risk at 55 and 69% accuracy, for ‘Braeburn’ and ‘Pacific Rose’ apples. These prediction accuracies are about 40% better than the accuracy expected by random selection at 39 and 49%, respectively. The models predicted 70% and 88% of the batches with high levels of shrivel for ‘Braeburn’ and ‘Pacific Rose’ apples, respectively. The successful identification of at-risk batches of fruit will allow the industry to employ appropriate management strategies to minimise weight loss and the development of shrivel in storage. INTRODUCTION Excessive weight loss in pipfruit leads to shrivel, a condition characterised by a wrinkled skin appearance (Hatfield and Knee, 1988). Anecdotal information from the industry indicates that there is considerable variability in the incidence and severity of shrivel development and levels of weight loss among individual apples within a packaging system (Maguire, 1998). High levels of shrivel can impose significant costs on both the grower and the exporter. Fruit with a high incidence of shrivel will either be discounted to ensure sale, or repacked. If the level of shrivel is severe the fruit will be disposed of as they are unmarketable. All of these scenarios result in lost revenue, added costs, or both. Therefore, predicting fruit with high risk of shrivel offers a significant cost advantage to the industry. During the 1999/2000 season data was collected over 2000 batches of fruit (fruit harvested a the same time from a known area in an orchard) inspected between harvest and 140 days storage show that nearly 20 % of batches inspected had 2 % or greater incidence of shrivel. Some samples had 22 % of fruit showing signs of shrivel, Proc. Int. Conf. Quality in Chains Eds. Tijskens & Vollebregt Acta Hort. 604, ISHS 2003 256 confirming there is considerable variability in the incidence and severity of shrivel development among batches of fruit from different growers. Weight loss during storage is generated from two processes: carbon loss from respiration and water loss. Maguire et al. (1999a) found that in commercial storage (0.5C and approximately 85 % relative humidity) variability in both weight loss and shrivel are largely determined by differences in the rate of water loss from fruit in storage. The rate of water loss ( rH O ' 2 ; mol.s) from fruit can be described using the steady state solution of Fick's first law of diffusion (Nobel, 1991):