Postharvest Biology and Technology 43 (2007) 121–127 Increasing the rate of ripening of date palm fruit (Phoenix dactylifera L.) cv. Helali by preharvest and postharvest treatments Mohamed A. Awad ∗ College of Food and Agriculture, Department of Arid Land Agriculture, United Arab Emirates University, P.O. Box 17555, Al-Ain, UAE Received 27 April 2006; accepted 20 August 2006 Abstract ‘Helali’ is a late season date palm cultivar. At the mature (Bisir) stage, the fruit are astringent as a result of high contents of soluble tannins, and removal of tannins is necessary for the fruit to be edible. During the harvesting season, only 30–40% of the total fruit might normally ripen (Rutab stage) on the tree and the remaining fruit fail to ripen. This study showed that bunch bagging with different materials such as black or blue polyethylene bags, white ‘agrlsafe’ (polypropylene fleece) and paper bags during the growing season significantly increased the rate of fruit ripening and increased Rutab yield per bunch. In this respect, black and blue polyethylene bags were the most effective followed by ‘agrlsafe’ and paper bags. Preharvest ethrel application significantly increased Rutab fruit yield per bunch compared to the controls. There were no significant differences in Rutab yield per bunch between sprays or injection of ethrel into the bunch peduncle. Postharvest dipping of fruit at the Bisir stage in ethrel at 4.2 ml/l and abscisic acid at 1.0 mM significantly enhanced ripening, compared to the controls. However, ABG-3168 (an ethylene blocker) application at 3.33 g/l significantly inhibited ripening, suggesting a role for ethylene in the ripening process. Ethanol vapor significantly hastened ripening of Bisir fruit over 10 days at ambient conditions in desiccators. The response of immature fruit (according to fruit density and TSS) to ethanol vapor was much greater than mature ones. Also, immersion of fruit in water for 10 h significantly increased fruit ripening compared to the controls, but to a lesser extent. It is concluded that ‘Helali’ date ripening could be hastened by bunch bagging during growth, or by exposing the Bisir fruit to ethanol vapor following harvest. Neither treatment showed any negative impact on the overall quality characteristics of ripe fruit, suggesting that they may be practical tools for increasing the ripening rate of Bisir ‘Helali’ dates. © 2006 Elsevier B.V. All rights reserved. Keywords: Postharvest; Ripening; Bagging; Quality; Phoenix dactylifera L.; Date palm 1. Introduction Date palm is the most successful and important subsis- tence crop in most of the hot arid desert regions (Botes and Zaid, 1999). Generally, whole dates are harvested and mar- keted at three stages of development: mature firm (Bisir or Khalal), full ripe (Rutab) and dry (Tamr). The decision for harvesting at one or other stage depends on cultivar charac- teristics, especially soluble tannins levels, climatic conditions and market demand (Glasner et al., 1999). ‘Helali’ is one of late season date palm cultivars being extensively cultivated in the Gulf region. At the mature (Bisir) stage, the fruit are ∗ Permanent address: Faculty of Agriculture, Pomology Department, Man- soura University, El-Mansoura, Egypt. Tel.: +971 3 7133361; fax: +971 3 7632384. E-mail address: Mohamedawad@uaeu.ac.ae. astringent as a result of high contents of soluble tannins, and removal of tannins is necessary for the fruit to be edible. The fruit do not ripen evenly, even in the same bunch, and consequently several harvests (10–15) are required during the harvest season (early August to late November). How- ever, only 30–40% of the total fruit might normally ripen on tree and the remaining fruit fail to ripen, causing eco- nomic loss. Thus, hastening fruit ripening on or even off the tree is a critical process. Generally, the rate of fruit ripening is much higher during August and sharply declines during September, October and November. The remarkable decrease in temperatures occurring during this period might be con- nected with such ripening failure. Therefore, bunch bagging might increase accumulation of heat units around the fruit and hasten ripening. The rise in ethylene production accompanying the cli- macteric is a major regulatory event in the ripening of many 0925-5214/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.postharvbio.2006.08.006