Sensitivity of Dates to Acetic Acid and Ethrel in Relation to Soluble Tannins Content in the Astringent Fruits of Aum El- Ferakh at the Khalal Stage

In spite of the numerous-available clones and cultivars of date palm, few of them produce non-astringent dates at the khalal stage. The astringent fruit must convert to the rutab stage to be edible as fresh dates which means the conversion of soluble tannins to the insoluble form. Applications of the ethylenereleasing compound, namely, Ethrel, even at very high concentrations failed to induce rutab development in astringent fruit at the khalal stage. This research was conducted to investigate the involvement of soluble tannins in the sensitivity of tissue to ripening (rutab) enhancers such as Ethrel and acetic acid. This study was carried out during the two successive seasons 2004 and 2005 using Aum El-Ferakh cultivar as a model system that is very rich in soluble tannins at the khalal stage. After surface sterilizing the harvested fruits from the same trees, fruit at the full khalal were treated by dipping for 20 mins in one of the treatment solutions. The treatments included: acetic acid at three concentrations, 1, 3, and 5% (v/v) and Ethrel at 1000, 2000, and 3000 ppm, in addition to the control (dipping in water). Fruits were left on bench for 6 days at 22±2°C then assessed for rutab development, soluble tannins and other quality parameters. The data revealed that acetic acid at all used concentrations were able to induce rutab development while Ethrel concentrations failed to achieve that as was the case with the control fruits. J.Agric.&Env.Sci.Alex.Univ.,Egypt Vol.5 (2)2006 2 Meanwhile, the concentration of soluble tannins significantly decreased in both seasons especially with acetic acid at 3 and 5% while Ethrel-treated fruits at all concentrations had similar amount of soluble tannins to that found in the control. As a result of the conversion to the rutab stage by acetic acid treatments, there was a decline in fruit weight by the end of the experiment while fruit weight of Ethrel-treated fruits did not vary from that of the control. Other fruit quality parameters were also assessed such as weight loss, flesh weight, rag weight, TSS, acidity and vitamin C. This study provided experimental evidences that Ethrel treatment was sensitive to the presence of soluble tannins in fruit tissue while acetic acid was not. Acetic acid was also able to reduce soluble tannins and induce rutab