**7. Conclusion**

*Antioxidants*

further investigation.

water-irrigated dates.

showed a weak correlation (R<sup>2</sup>

**6. Limitations of this work**

the apparent variability of the date antioxidant activity.

*5.2.5 Variation of antioxidant priorities due to abiotic stress*

In a study of the effect of sewage water irrigation of date palm tree in the antioxidant constituency of three Saudi date cultivars, Abdulaal et al. [105] reported higher levels of TP; TF; increased antioxidant activity using ABTS, DPPH, and the formation of phosphor-molybdenum complex test; as well as higher activities of peroxidase, polyphenol oxidase, and glutathione-S-transferase in dates irrigated with sewage water as compared to irrigation with municipal water. The increased level of these parameters was accompanied with higher accumulation of heavy metals (Cr, Cu, Fe, Mn, Pb, and Zn) in the sewage water-irrigated dates. The three studied cultivars showed differential responses regarding TP and TF. TP level in Agwa and Safawi increased by 28–30% over the control, while in Anbr cultivar it increased by only 8%. Furthermore, the extent of increase in TF in the three cultivars was somewhat similar (Agwa, 41%; Anbr, 50%; and Safawi, 50%). These results are suggestive of different response mechanisms and need

Al-Busaidi et al. [106] recently reported that while the levels of Fe, Zn, and Ni were relatively higher in the treated sewage water irrigated than the groundwater irrigated, whereas the levels of Cu, Cd, Pb, and B were significantly higher in date fruits irrigated with groundwater than sewage water irrigated. These contradicting findings may be partially attributed to the level of treatment of sewage water used, i.e., secondary or tertiary treatment. In our own findings (unpublished) with locally grown several date cultivars, no significant difference was found in the accumulation of several heavy metals between groundwater and secondary-treated sewage

*5.2.6 Association of antioxidant consistency and antioxidant activity in date fruits*

Khenazy (0.89), Helali (0.85), Lonet-Mesaed (0.64), but was not significantly correlated in Mejdool (0.46). In contrast, Medjool exhibited high correlation

In vitro methods commonly used to estimate antioxidant activity include ABTS, DPPH, FRAP, and ORAC. Like many other plant-based foods, a clear relationship between the antioxidant content and antioxidant activity exists in date fruits, though its extent varies widely. For example, the DPPH method, widely used to estimate the radical scavenging activity of antioxidants was found [54] to be highly correlated to TP content in four Saudi cultivars, namely, Barhee (R2

 = 0.91) between DPPH and total soluble tannin concentration. The correlation of DPPH and phenols, tannins, and flavonoid content of 12 products made from two Spanish date cultivars was also high, 0.765, 0.747, and 0.822, respectively [76]. On the other hand, plotting the IC50 (amount in μg/ml which gives 50% inhibition of DPPH quenching) of 18 cultivars from Saudi Arabia against their total phenolics

phenolic content plays as the major antioxidant in date fruits but also as a cause of

Due to many constrains, this chapter addresses only one aspect of the variability of antioxidants in dates, namely, the TP content. The purpose of this chapter is to shed light and to expose the problem in the hope that other opportunities will be available to address the issue more comprehensively. The issue can be treated in depth with the inclusion of published values of other antioxidants as well as antioxidant

= 0.0341) [27]. These findings not only indicate that

= 0.96),

**116**

(R2

Variability of levels of phytochemicals (plant-based) is a common phenomenon. However, the magnitude of such variability is influence by natural and artificial causes. Examination of values of the TP content in dates published over the last two decades reveals wide disparity that needs to be seriously addressed. This large variability creates a challenge that makes it difficult to deal with the validity and reliability of published values and may hinder or reduce its practical usefulness. Overcoming this problem and related issues requires collaboration between many groups from different countries. With many research teams interested in the date palm and its fruit (dates), this is possible and achievable and requires someone who takes the initiative.
