Postharvest Biology and Technology 53 (2009) 72–76 Contents lists available at ScienceDirect Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio Influence of water and ABA supply on the ripening pattern of avocado (Persea americana Mill.) fruit and the prediction of water content using Near Infrared Spectroscopy Robert J. Blakey ∗ , John P. Bower, Isa Bertling Horticultural Science, Department of Agricultural Plant Sciences, School of Agricultural Science and Agribusiness, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa article info Article history: Received 5 January 2009 Accepted 12 March 2009 Keywords: Avocado ABA Water Infusion NIR Non-destructive measurement abstract Avocado fruit are highly variable, and even those graded for similar size and appearance do not behave in the same manner after harvest. This is particularly problematical for those involved in sales to the “ready-ripe” market. These operations are faced with a high variation in the rate of ripening within a consignment, causing logistical difficulties. Fruit water content (or its complement dry matter) has a major impact on-line ripening and has hence been used as the maturity marker in the South African avocado industry. Presently, fruit water content is destructively measured using a representative sample as an indicator of when to post-harvest. In order to investigate if fruit water content and/or abscisic acid triggers fruit ripening, water or ABA was infused into commercially mature, but non-ripe avocado fruit. The fruit ripening, mass, CO 2 and ethylene production patterns were determined over the ripening period. By infusing water through the pedicle, the variation in days to ripening was decreased without any effect on the number of days to ripening. ABA infusion hastened ripening but did not affect the variation in days to ripening. It is therefore suggested that the fruit water content at harvest forms the baseline condition from which the trigger for ripening is determined, while post-harvest water loss and ABA modulate and stimulate ripening, respectively. Furthermore, an equation was developed using Near Infrared Spectroscopy (NIRS) to measure mesocarp water content (R 2 = 0.92, SE = 1.8% MC). It is postulated that on line sorting of fruit using NIRS, based on time to ripen, would result in consignments of fruit with less ripening variation, thereby solving the industry’s logistical problem of fruit which have a wide spread of ripening being packed into one carton. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The avocado (Persea americana Mill.) is an unusual fruit, in that ripening, which is associated with, but not dependent on, softening and colour change, which does not normally occur on the tree but only after harvest (Bogin and Wallance, 1965). The decision to har- vest must therefore be made independent of visible measurements and is currently based on either the oil content of the fruit (Young and Lee, 1978), the dry matter content or the water content as in South Africa (Hofman et al., 2002; Clark et al., 2003). Dry matter and water content are complementary, i.e. summing to 100%. Variable ripening in consignments of avocados is creating a sub- stantial logistical problem, especially when fruit are ripened in pre-packaging facilities (Bower et al., 2007). While some of the causes of the variation in the rate of ripening amongst fruit of simi- ∗ Corresponding author. Tel.: +27 33 260 6108; fax: +27 33 260 5073. E-mail address: robblakey@gmail.com (R.J. Blakey). lar size and origin are known, these factors do not fully explain this variation. The protracted flowering period, which occurs in most avocado production areas (Salazar-García et al., 1998), and sun- exposure, can delay ripening by approximately 1.5d (Woolf et al., 1999). This results in a high variation in physiological age of fruit from a single tree. An even greater variation can hence be expected within one orchard, and when fruit from a variety of orchards are shipped in one consignment to overseas markets. The rate of post-harvest ripening is deemed to be related to fruit maturity, as fruit picked at the beginning of the picking sea- son take longer to ripen than fruit picked at the end of the season (Zauberman and Schiffman-Nadel, 1972; Adato and Gazit, 1974). Acceptable norms for the water content or dry matter have been calculated from large numbers of fruit, but individual fruit variabil- ity calls into question the accuracy and usefulness of these norms, particularly as the diagnostic methods are destructive, and can thus only be applied to small samples of consignments. In order to solve the problem of variability in ripening within the avocado trade, it is necessary to ascertain whether measuring fruit water content at 0925-5214/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2009.03.004