**5. Discussion**

#### **5.1 Variability of TP value and its implication**

In the fields of public health, nutrition, and nutritional epidemiology, reliable and accurate estimates of concentration of a nutrient in a food commodity is important for estimating the daily consumption (intake) for an individual within a population, as well as for setting the average, upper, and lower limits of that nutrient for official recommendations and guidelines. The TP content is neither (yet) considered as a nutrient nor as a single chemical compound that can be reduced to the level of an officially declared nutrient such as ascorbic acid and treated similarly. TP is rather an experimentally measured value representing a chemical measure for an inherently great numbers of diverse groups of secondary metabolites or phytochemicals, simple and polyphenols, with many biological functions vital for the survival of their producers (plants) and for their consumer. Although TP is not a single entity, but, theoretically (and hypothetically) speaking, it is similar, in a way, to the groups of foods (proteins, carbohydrates, and lipids) which are characterized by high diversity of its nature, structure, and consistency. For this, one may be allowed to deal with TP content in a similar way, taking into consideration that TP content, at present, is not among the macro- and micronutrients.

**113**

*Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content…*

Admittedly, large variation widely exists in biological measurements. In nutritional sciences, nutrient variability is a common place. A nutrient may vary in its numerical values for many reasons, and the magnitude of variation can be very large [92]. In the analysis of the already published values of the TP content date fruits for a large number of cultivars from different countries, regions, and continents, it can be concluded that the magnetite of variation in all edible stages, and in the Tamer stage in particular, is very high, in the order of hundreds, when extreme values and outliers are removed, and perhaps in thousands when these values are included.

This situation represents an unfavorable challenge for researchers, nutritionists, end users, and policy makers alike. To illustrate, a researcher may ask of the typical value of TP content of the date fruit in general or a typical value for a specific cultivar. In fact, in the literature, it is common to declare nutritional values of dates based on one or two cultivars with the assumption that these are true representative

Does such variability is due to natural variation, or should we take into consideration the uncertainty, or a combination of both? This remains unclear and needs to be answered. While variability is defined as the occurrence of multiple values for a quantity at different locations and refers to the inherent heterogeneity or diversity of data in an assessment, uncertainty refers either to the lack of knowledge of the value of some quantity (qualitative uncertainty) or the usage of non-precise measurement methods of (quantitative uncertainty) may come from the use [93]. The source of uncertainty can be of many types including random errors, sampling, and measurement errors. Variability can be characterized but cannot be reduced, whereas uncertainty can be reduced, which, if appropriately applied, can lead to

The variability of the values of the TP content for date fruits is evident by the various estimates of dispersion (see **Tables 4**–**6**). Causes of such dispersion are not known nor can be investigated unless the experimental conditions of the actual analysis can be traced back. In such situation, with little or no knowledge about of the data quality and the associated errors, one may speculate that data of the values of TP of dates do not merely reflect a natural variation, but element(s) of uncer-

Variation in antioxidants and antioxidant activity is not limited to variation due to cultivars, maturity stage, and geographical or agronomical conditions. Rather, antioxidant activity varies between dates within the same bunch and even within the same fruit. In the following section, some of causes of the antioxidant

Many studies examined the effect of maturity stage in the antioxidant consistency and activity [25, 35–38, 41, 54, 73, 74]. There is a general agreement that the highest antioxidant activity is found in Khalal stage and the lowest in Tamer stage. Sourial et al. [94] reported data of five cultivars exhibiting a sigmoidal decline of tannins. The remaining tannin content at Tamer stage represented 33–43% of that at Rutab and Khalal stages. The kinetics of degradation of total phenolic content during these three stages was also reported [42]. TP content declines to follow first-order reaction in the Tamer stage which represents between 25 and 40% of the Khalal stage. Generally, red cultivars at Khalal stage possess greater antioxidant

*DOI: http://dx.doi.org/10.5772/intechopen.83851*

of the vast majority of cultivars, i.e., [91].

increased confidence in the estimates [93].

**5.2 Sources of variability of antioxidant activity in dates**

*5.2.1 Variation of antioxidant properties due to maturity stage*

tainty cannot be excluded.

will be presented.

activity than yellow cultivars.

#### *Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content… DOI: http://dx.doi.org/10.5772/intechopen.83851*

Admittedly, large variation widely exists in biological measurements. In nutritional sciences, nutrient variability is a common place. A nutrient may vary in its numerical values for many reasons, and the magnitude of variation can be very large [92]. In the analysis of the already published values of the TP content date fruits for a large number of cultivars from different countries, regions, and continents, it can be concluded that the magnetite of variation in all edible stages, and in the Tamer stage in particular, is very high, in the order of hundreds, when extreme values and outliers are removed, and perhaps in thousands when these values are included.

This situation represents an unfavorable challenge for researchers, nutritionists, end users, and policy makers alike. To illustrate, a researcher may ask of the typical value of TP content of the date fruit in general or a typical value for a specific cultivar. In fact, in the literature, it is common to declare nutritional values of dates based on one or two cultivars with the assumption that these are true representative of the vast majority of cultivars, i.e., [91].

Does such variability is due to natural variation, or should we take into consideration the uncertainty, or a combination of both? This remains unclear and needs to be answered. While variability is defined as the occurrence of multiple values for a quantity at different locations and refers to the inherent heterogeneity or diversity of data in an assessment, uncertainty refers either to the lack of knowledge of the value of some quantity (qualitative uncertainty) or the usage of non-precise measurement methods of (quantitative uncertainty) may come from the use [93]. The source of uncertainty can be of many types including random errors, sampling, and measurement errors. Variability can be characterized but cannot be reduced, whereas uncertainty can be reduced, which, if appropriately applied, can lead to increased confidence in the estimates [93].

The variability of the values of the TP content for date fruits is evident by the various estimates of dispersion (see **Tables 4**–**6**). Causes of such dispersion are not known nor can be investigated unless the experimental conditions of the actual analysis can be traced back. In such situation, with little or no knowledge about of the data quality and the associated errors, one may speculate that data of the values of TP of dates do not merely reflect a natural variation, but element(s) of uncertainty cannot be excluded.

#### **5.2 Sources of variability of antioxidant activity in dates**

Variation in antioxidants and antioxidant activity is not limited to variation due to cultivars, maturity stage, and geographical or agronomical conditions. Rather, antioxidant activity varies between dates within the same bunch and even within the same fruit. In the following section, some of causes of the antioxidant will be presented.

#### *5.2.1 Variation of antioxidant properties due to maturity stage*

Many studies examined the effect of maturity stage in the antioxidant consistency and activity [25, 35–38, 41, 54, 73, 74]. There is a general agreement that the highest antioxidant activity is found in Khalal stage and the lowest in Tamer stage. Sourial et al. [94] reported data of five cultivars exhibiting a sigmoidal decline of tannins. The remaining tannin content at Tamer stage represented 33–43% of that at Rutab and Khalal stages. The kinetics of degradation of total phenolic content during these three stages was also reported [42]. TP content declines to follow first-order reaction in the Tamer stage which represents between 25 and 40% of the Khalal stage. Generally, red cultivars at Khalal stage possess greater antioxidant activity than yellow cultivars.

*Antioxidants*

regardless of the country.

among the listed four cultivars.

**5.1 Variability of TP value and its implication**

not among the macro- and micronutrients.

**5. Discussion**

**4.2 Variability of TP values of selected date cultivars from different countries**

**Table 5** presents estimates of variability and central tendency of TP content of selected date cultivars reported from different countries. Normally, in nutritional epidemiology, the variance represents the true variability of nutrient content. The variability of continuous type of results produced experimentally by some assays is evaluated by the CV rather than SD, since the CV is a standardization of the SD (CV = SD/mean \* 100). Using CV allows for direct comparison of estimates of variability regardless of the magnitude of the level of analyte under investigation. In many biological fields, a twofold difference in measurements of the same sample can be acceptable as the upper limit of variability. Furthermore, a CV of 40% can be tolerated in nutrient estimation for food labeling and nutrient intake calculation [90]. Since there is no reference value or a benchmark for the variability of TP content in dates to compare with, the above recommendation may be used to facilitate comparison. The variance and CV, as well as other estimates of dispersion, are very large. The largest variance was found for Ajwa, whereas Deglet Nour exhibited the lowest variance. The CV was even more pronounced as an evidence of the vast variability, with some cultivar possessing CV values of more than 100%. Estimates presented on **Table 5** demonstrate the extent of variability of the TP content values

**Table 6** presents similar statistics based on data obtained from studies originated from a single country for a particular date cultivar. This table illustrates the extent of variability of the TP content within a country. For example, TP values of Khalas cultivar from two countries (Saudi Arabia and Oman) showed large variation within cultivar and between the two countries, while the TP values of selected date cultivars taken from different studies carried out within that country are similar. Again, all estimates of variability are indicative of the large disparity of the published TP values. Notably, Ajwa cultivar of Saudi Arabia, which is grown almost exclusively in the holy city, Al-Madina Al-Munawara, possessed the largest CV (%)

In the fields of public health, nutrition, and nutritional epidemiology, reliable and accurate estimates of concentration of a nutrient in a food commodity is important for estimating the daily consumption (intake) for an individual within a population, as well as for setting the average, upper, and lower limits of that nutrient for official recommendations and guidelines. The TP content is neither (yet) considered as a nutrient nor as a single chemical compound that can be reduced to the level of an officially declared nutrient such as ascorbic acid and treated similarly. TP is rather an experimentally measured value representing a chemical measure for an inherently great numbers of diverse groups of secondary metabolites or phytochemicals, simple and polyphenols, with many biological functions vital for the survival of their producers (plants) and for their consumer. Although TP is not a single entity, but, theoretically (and hypothetically) speaking, it is similar, in a way, to the groups of foods (proteins, carbohydrates, and lipids) which are characterized by high diversity of its nature, structure, and consistency. For this, one may be allowed to deal with TP content in a similar way, taking into consideration that TP content, at present, is

**112**

#### *5.2.2 Variation of antioxidant properties within a single date fruit*

Date fruits harvested from the same bunch at the same time may possess different levels of antioxidants, though may be statistically insignificant (need further studies). Within the same bunch, dates are differentially exposed to sunlight. Sunlight affects biosynthesis of simple and polyphenolic compounds including flavonoids. In many fruits, biosynthesis of polyphenolic compounds is an adoptive process [95]. High light induces the expression of many early and late genes involved in biosynthesis of flavonoids. Dates located inside the bunch are the least to receive sunlight, compared to those at the peripheral. This is also valid with regard to different bunches within the same tree.

Within a single date fruit, the distribution of antioxidants in the tissues is not homogenous. Guo et al. [96] reported that the peel of unspecified date cultivar possessed 2.4 times higher antioxidant activity than the pulp, 16.69 compared to 6.98 mmol/100 g WW (FRAP assay), respectively. A recent study by Djouab et al. [97], using Tamer of the yellow Algerian cultivar Mesh Degla, showed that the level of TP in the whole flesh, peel, brown tissue, and white tissue was 206, 247.3, 185.2, and 66.63 mg GAE/100 g DM, respectively. In this study, the antioxidant activity followed the same trend. Generally, fruit peels possess higher antioxidant than the flesh [96]. Depending on date cultivar, peel may contribute between 50 and 70% of the antioxidant, despite constituting only 3–5% of the total edible weight. Due to their vital biological role as protectants, many potent polyphenolic antioxidants are essentially localized in the peel, particularly during Khalal stage, leading to higher antioxidant activity. Furthermore, the white tissue of the flesh, the most inner part, possesses the least antioxidant/activity as compared to other tissues. Within the brownish tissue, condensed tannins are, usually, stored in the stone cells.

#### *5.2.3 Variation of antioxidant activity due to diverse polyphenolic composition*

Antioxidant property in plant-based food is largely due to the natural polyphenolic antioxidants. Redox properties of these natural antioxidants make them function as reducing agents, free radical scavengers, hydrogen donors, chelators, and metal. The phenolic consistency of date fruits, including flavonoids, has been recently studied by many research groups [18, 22–24, 38, 62, 68–70, 74, 98–100].

Phenolic acids found in dates belong mainly to benzoic or cinnamic acid derivatives. However, the distribution of phenolic acids varies considerably among different date cultivars. El-Arem et al. [38] reported a significant difference in the phenolic compounds amounts between maturation stages for the majority of cultivars. These groups identified two newly described phenolics in dates (hydroxyphenylacetic and phenylacetic acids). A contrasting example of the dynamic nature (or fluctuation) of phenolic acids in date fruits is cinnamic acid (CNA) which was also reported by this group [38]. CNA was not detected in the three maturity stages (K, R, T) of cultivars Gondi and Rotb Ahmar; however, it significantly increased during maturation of cultivar Gosbi and detected in comparable amount in R and T stages but not in K in the cultivar Khalt Dhahbi.

Farag et al. [24] recently identified 44 metabolites in 18 Saudi cultivars, of which 20 were flavonoids and 4 were hydroxycinnamates but also noted that several of previously reported predominant phenolic acids were not found in their study. While free phenolic acids are present in Rutab stage in most cultivars, albeit at lower concentration, the semidry cultivar Sukkari had no detectable free and glycosylated phenolic acids at Rutab stage and contained only esterified phenolics. Moreover, the fate of a particular phenolic acid or flavonoid differs between date cultivars (**Figure 4**). Among six different cultivars, Kursinszki et al. [98] reported that rhamnosyl

**115**

tannins, over the other.

*Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content…*

hexosyl methyl luteolin was a major constituent in all of them, albeit at different levels, whereas hexosyl methyl luteolin sulfate was a major constituents in only three cultivars Khenaizi, Khalas, and Lulu. Among these cultivars, Lulu was characterized by being relatively low in flavonoid content. The Al-Medina dates were distinct by the presence of rhamnosyl hexosyl luteolin. A very recent detailed study by Abu-Reidah et al. [101] has identified 52 phenolic compounds in five various parts of the date palm tree including the edible portion (skin and pulp). The distribution (and the quantification) of phenolic compounds in the edible proton of the date fruit is of particular interest on this review. The combined number of peaks identified in pulp and skin was 22, of which 17 were found in pulp and 16 in skin, with 12 peaks being shared (~55%). Interestingly, the edible proton of dates was lacking of ferulic acid derivatives despite its known abundant in both, the skin and pulp. To the contrary, luteolin was only found in the skin, while its derivatives may be found, unequally, in both tissues. The methyl glycoside derivatives, which is consistent with specialization and func-

*Distribution of free ( ), esterified ( ), and glycosylated ( ) phenolic acids in five date fruits at two* 

*maturation stages Rutab (fresh) and sun-dried Tamer. Data extracted from Khojah [53].*

tionality of the plant part, were also lacking from the edible portion.

*5.2.4 Variation of antioxidants due to pollination, bagging, and thinning*

Date palm tree is a dioecious monocotyledonous, and fertilization occurs either naturally or is carried out artificially. Pollens obtained from one cultivar can fertilize another cultivar. However, pollination has significant impacts in the physical and chemical properties of the resultant dates. It affects, among other things, the fruit set, size, time of ripening, seeds, eating quality, as well as the chemical constituency of the date including antioxidants, an effect known in plant science as metaxenia. Maryam [72] reported that pollen patents had the potential to significantly influence total phenolics in dates. Using eight male pollen patents to fertilize two different cultivars, the TP of Hallawi cultivar increased from 190 mg GAE/100 g in the control to 491 mg GAE/100 g and from 212 to 480 mg GAE/100 g in Khadhrawi cultivar. Similar effect was also found with ascorbic acid. Farag et al. [102] found that one of two pollinator types significantly increased the content of anthocyanin and ascorbic acid, but not

The practice of fruit thinning, either by reducing the number of fruits per bunch

or the number of bunches per tree, leads to significant quality enhancement in dates. Several methods of thinning are available for date palm trees. This practice was found to reduce the tannins content in some date cultivars [103]. Bunch bagging of the same cultivar with perforated blue polyethylene increased ascorbic acid level, decreased the total soluble tannins concentrations and peroxidase activity,

and had no significant effect on total phenolic content [104].

*DOI: http://dx.doi.org/10.5772/intechopen.83851*

**Figure 4.**

*Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content… DOI: http://dx.doi.org/10.5772/intechopen.83851*

#### **Figure 4.**

*Antioxidants*

*5.2.2 Variation of antioxidant properties within a single date fruit*

regard to different bunches within the same tree.

Date fruits harvested from the same bunch at the same time may possess different levels of antioxidants, though may be statistically insignificant (need further studies). Within the same bunch, dates are differentially exposed to sunlight. Sunlight affects biosynthesis of simple and polyphenolic compounds including flavonoids. In many fruits, biosynthesis of polyphenolic compounds is an adoptive process [95]. High light induces the expression of many early and late genes involved in biosynthesis of flavonoids. Dates located inside the bunch are the least to receive sunlight, compared to those at the peripheral. This is also valid with

Within a single date fruit, the distribution of antioxidants in the tissues is not homogenous. Guo et al. [96] reported that the peel of unspecified date cultivar possessed 2.4 times higher antioxidant activity than the pulp, 16.69 compared to 6.98 mmol/100 g WW (FRAP assay), respectively. A recent study by Djouab et al. [97], using Tamer of the yellow Algerian cultivar Mesh Degla, showed that the level of TP in the whole flesh, peel, brown tissue, and white tissue was 206, 247.3, 185.2, and 66.63 mg GAE/100 g DM, respectively. In this study, the antioxidant activity followed the same trend. Generally, fruit peels possess higher antioxidant than the flesh [96]. Depending on date cultivar, peel may contribute between 50 and 70% of the antioxidant, despite constituting only 3–5% of the total edible weight. Due to their vital biological role as protectants, many potent polyphenolic antioxidants are essentially localized in the peel, particularly during Khalal stage, leading to higher antioxidant activity. Furthermore, the white tissue of the flesh, the most inner part, possesses the least antioxidant/activity as compared to other tissues. Within the brownish tissue, condensed tannins are, usually, stored in the stone cells.

*5.2.3 Variation of antioxidant activity due to diverse polyphenolic composition*

Antioxidant property in plant-based food is largely due to the natural polyphenolic antioxidants. Redox properties of these natural antioxidants make them function as reducing agents, free radical scavengers, hydrogen donors, chelators, and metal. The phenolic consistency of date fruits, including flavonoids, has been recently studied by many research groups [18, 22–24, 38, 62, 68–70, 74, 98–100]. Phenolic acids found in dates belong mainly to benzoic or cinnamic acid deriva-

tives. However, the distribution of phenolic acids varies considerably among different date cultivars. El-Arem et al. [38] reported a significant difference in the phenolic compounds amounts between maturation stages for the majority of cultivars. These groups identified two newly described phenolics in dates (hydroxyphenylacetic and phenylacetic acids). A contrasting example of the dynamic nature (or fluctuation) of phenolic acids in date fruits is cinnamic acid (CNA) which was also reported by this group [38]. CNA was not detected in the three maturity stages (K, R, T) of cultivars Gondi and Rotb Ahmar; however, it significantly increased during maturation of cultivar Gosbi and detected in comparable amount in R and T

Farag et al. [24] recently identified 44 metabolites in 18 Saudi cultivars, of which 20 were flavonoids and 4 were hydroxycinnamates but also noted that several of previously reported predominant phenolic acids were not found in their study. While free phenolic acids are present in Rutab stage in most cultivars, albeit at lower concentration, the semidry cultivar Sukkari had no detectable free and glycosylated phenolic acids at Rutab stage and contained only esterified phenolics. Moreover, the fate of a particular phenolic acid or flavonoid differs between date cultivars (**Figure 4**). Among six different cultivars, Kursinszki et al. [98] reported that rhamnosyl

stages but not in K in the cultivar Khalt Dhahbi.

**114**

*Distribution of free ( ), esterified ( ), and glycosylated ( ) phenolic acids in five date fruits at two maturation stages Rutab (fresh) and sun-dried Tamer. Data extracted from Khojah [53].*

hexosyl methyl luteolin was a major constituent in all of them, albeit at different levels, whereas hexosyl methyl luteolin sulfate was a major constituents in only three cultivars Khenaizi, Khalas, and Lulu. Among these cultivars, Lulu was characterized by being relatively low in flavonoid content. The Al-Medina dates were distinct by the presence of rhamnosyl hexosyl luteolin. A very recent detailed study by Abu-Reidah et al. [101] has identified 52 phenolic compounds in five various parts of the date palm tree including the edible portion (skin and pulp). The distribution (and the quantification) of phenolic compounds in the edible proton of the date fruit is of particular interest on this review. The combined number of peaks identified in pulp and skin was 22, of which 17 were found in pulp and 16 in skin, with 12 peaks being shared (~55%). Interestingly, the edible proton of dates was lacking of ferulic acid derivatives despite its known abundant in both, the skin and pulp. To the contrary, luteolin was only found in the skin, while its derivatives may be found, unequally, in both tissues. The methyl glycoside derivatives, which is consistent with specialization and functionality of the plant part, were also lacking from the edible portion.

#### *5.2.4 Variation of antioxidants due to pollination, bagging, and thinning*

Date palm tree is a dioecious monocotyledonous, and fertilization occurs either naturally or is carried out artificially. Pollens obtained from one cultivar can fertilize another cultivar. However, pollination has significant impacts in the physical and chemical properties of the resultant dates. It affects, among other things, the fruit set, size, time of ripening, seeds, eating quality, as well as the chemical constituency of the date including antioxidants, an effect known in plant science as metaxenia. Maryam [72] reported that pollen patents had the potential to significantly influence total phenolics in dates. Using eight male pollen patents to fertilize two different cultivars, the TP of Hallawi cultivar increased from 190 mg GAE/100 g in the control to 491 mg GAE/100 g and from 212 to 480 mg GAE/100 g in Khadhrawi cultivar. Similar effect was also found with ascorbic acid. Farag et al. [102] found that one of two pollinator types significantly increased the content of anthocyanin and ascorbic acid, but not tannins, over the other.

The practice of fruit thinning, either by reducing the number of fruits per bunch or the number of bunches per tree, leads to significant quality enhancement in dates. Several methods of thinning are available for date palm trees. This practice was found to reduce the tannins content in some date cultivars [103]. Bunch bagging of the same cultivar with perforated blue polyethylene increased ascorbic acid level, decreased the total soluble tannins concentrations and peroxidase activity, and had no significant effect on total phenolic content [104].

#### *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 further investigation.

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 water-irrigated dates.

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

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 = 0.96), 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 (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 showed a weak correlation (R<sup>2</sup> = 0.0341) [27]. These findings not only indicate that phenolic content plays as the major antioxidant in date fruits but also as a cause of the apparent variability of the date antioxidant activity.

#### **6. Limitations of this work**

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

**117**

**Author details**

Abdulameer Allaith

provided the original work is properly cited.

\*Address all correspondence to: biolaith@gmail.com

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

Formerly at College of Science, University of Bahrain, Kingdom of Bahrain

*Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content…*

potential source of variability of date antioxidants can also be examined.

activities. Potential and appropriate statistical tools to investigate the issue are within and between subject analysis of variability and multivariate analysis. Uncertainty as a

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.

The author wishes to thank Mrs. Batool Abdul Wahab, Department of Biology, College of Science, University of Bahrain, for her tremendous efforts during the preparation of this chapter, doing literature searching and collecting and making

*DOI: http://dx.doi.org/10.5772/intechopen.83851*

**7. Conclusion**

**Acknowledgements**

them available.

*Antioxidants in Date Fruits and the Extent of the Variability of the Total Phenolic Content… DOI: http://dx.doi.org/10.5772/intechopen.83851*

activities. Potential and appropriate statistical tools to investigate the issue are within and between subject analysis of variability and multivariate analysis. Uncertainty as a potential source of variability of date antioxidants can also be examined.
