**3. Antioxidant in dates**

#### **3.1 The issue of large variability of total phenolic content**

Over the past two decades, several studies on antioxidant properties of date fruits have been published. These studies have contributed to increase our knowledge and understanding of these properties and the importance of dates as a food and its medical, therapeutical, and health virtues. However, the foresight of these studies finds great variations of levels and values of studied parameters of antioxidant of these results, which confuses the researcher/reader, leading to some skepticism and casting doubt.

To illustrate the magnitude of the problem and the importance of attempting to overcome this wide disparity, I will review here what Hammouda et al. [17] recently noted while comparing their findings with results of a previous published. Hammouda et al. [18] estimated the TP of two date cultivars from three geographical origins using an HPLC methodology and reported an average of 154 mg/whole fruit (or 126.3 mg/edible part of the fruit, average weight of a fruit was 10.2 g). When they compared their findings with values reported on the widely cited study of Al-Farsi and Lee [6], which reported that TP ranged between 194 and 240 mg/100 g of fruit, corresponding to ~19–24 mg per fruit, they concluded that (a quote): "We consider that our estimation better reflects the real concentration of total polyphenols in dates as phloroglucinolysis−HPLC is the only quantification method that takes into account the nonextractable PCs which represent the major part of polyphenols in dates and which are not quantified when a colorimetric assay is performed on a methanol extract."

Many researchers have faced a similar situation and may have reached similar conclusions, as evidenced by many comparative studies. Recently, Mishra et al. [19] reviewed and analyzed the abnormalities associated with reporting the antioxidant activity using DPPH methods. Whether one agrees or disagrees with the above statement made by [18] is not the issue here. The issue is that whether the huge disparity of experimentally obtained and numerically reported values of antioxidants and antioxidant activity on date fruits really reflect the phenomena of natural variability or a manifestation of otherwise.

**105**

**3.3 Data cleaning**

**3.4 Statistical analysis**

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

many assays used to estimate antioxidant activity (ABTS, DPPH, FRAP, etc.). Estimation of TP is usually performed using the well-established Folin– Ciocalteu (FC) colorimetric method or one of its variants with gallic acid (GA) being widely used as a standard for calibration [19]. Results are usually expressed as mg GAE/g or 100 g. The FC method is based on electron transfer reactions between the phenolic antioxidant(s) and the FC reagent. It is not specific for TP determination and is prone to interfering compounds presented in the sample leading to biased estimation. Reducing sugars which are present in high concentration in dates and ascorbic acid, which is present in substantial level at some developmental stages, are examples of these interfering compounds [20]. Most of the published

studies reporting TP in dates did not adequately address this issue.

Data used in this analytical review are of secondary type. They include the total phenolic (TP) content of 243 cultivars from 18 countries, covering the three potentially edible maturity stages, Khalal, Rutab, and Tamer (**Figure 1**). The selection of these datasets was based solely on relatedness and availability at the time of the preparation of this review. Values of TP were either copied and pasted from the published sources or extracted from graphs by using the online site WebPlotDigitizer [21]. A partial list of selected studies with some parameters of antioxidants and antioxidant activity is given in **Table 2**. **Table 3** lists countries of the recruited studies. Most published values of TF were reported as sampled (i.e., the fresh or dry weight of the edible portion of the date fruits). To make them comparable and meaningful, these weight values were recalculated and presented on a dry matter (DM) basis. When given, moisture content was used to calculate the moisture fraction, hence the DM. In the absence of moisture content, the following general moisture contents were used: Khalal (66%), Rutab (43%), and Tamer (22%). When oven-dried or lyophilized samples were indicated, the moisture content used value was 15%. Samples of date syrup and wasted dates were also included since they usually possess similar TP content.

The name of the same date cultivar in different countries may have different spellings. An example of this is the cultivar Barhi which has the following synonymous: Berhi = Burhi = Barhee = Barhy; Deglet Nour = Deglet Noor;

Sokary = Sukkari = Sukari; and Sofry = Sufry = Suffry. It was very essential for the

Outliers were statistically detected and removed from analysis. Removing of statistically detected outliers, at this stage of analysis, was based on convenience, simplifying the analysis, to examine their effects on estimates. Their analysis requires a more rigorous methodology, and perhaps these extreme values may represent a reality.

Excel (Microsoft) and SPSS (IBM, version 23) were used for statistical analysis

analysis to designate a single spelling for the same cultivar.

which included estimates of central tendency and variability.

In the following section, the total phenolic (TP) content reported in the literatures by many groups will be statistically analyzed. Selection of the TP content to illustrate the extent of variability and diversity of the antioxidant in dates is largely based on its commonality and convenience. The majority of the published studies dealing with antioxidants and antioxidant activity of dates (other plant based produces as well) reports TP as the prime parameter. Furthermore, TP content is highly correlated with

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

**3.2 Sources and preparation of dataset**

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

In the following section, the total phenolic (TP) content reported in the literatures by many groups will be statistically analyzed. Selection of the TP content to illustrate the extent of variability and diversity of the antioxidant in dates is largely based on its commonality and convenience. The majority of the published studies dealing with antioxidants and antioxidant activity of dates (other plant based produces as well) reports TP as the prime parameter. Furthermore, TP content is highly correlated with many assays used to estimate antioxidant activity (ABTS, DPPH, FRAP, etc.).

Estimation of TP is usually performed using the well-established Folin– Ciocalteu (FC) colorimetric method or one of its variants with gallic acid (GA) being widely used as a standard for calibration [19]. Results are usually expressed as mg GAE/g or 100 g. The FC method is based on electron transfer reactions between the phenolic antioxidant(s) and the FC reagent. It is not specific for TP determination and is prone to interfering compounds presented in the sample leading to biased estimation. Reducing sugars which are present in high concentration in dates and ascorbic acid, which is present in substantial level at some developmental stages, are examples of these interfering compounds [20]. Most of the published studies reporting TP in dates did not adequately address this issue.

#### **3.2 Sources and preparation of dataset**

Data used in this analytical review are of secondary type. They include the total phenolic (TP) content of 243 cultivars from 18 countries, covering the three potentially edible maturity stages, Khalal, Rutab, and Tamer (**Figure 1**). The selection of these datasets was based solely on relatedness and availability at the time of the preparation of this review. Values of TP were either copied and pasted from the published sources or extracted from graphs by using the online site WebPlotDigitizer [21]. A partial list of selected studies with some parameters of antioxidants and antioxidant activity is given in **Table 2**. **Table 3** lists countries of the recruited studies.

Most published values of TF were reported as sampled (i.e., the fresh or dry weight of the edible portion of the date fruits). To make them comparable and meaningful, these weight values were recalculated and presented on a dry matter (DM) basis. When given, moisture content was used to calculate the moisture fraction, hence the DM. In the absence of moisture content, the following general moisture contents were used: Khalal (66%), Rutab (43%), and Tamer (22%). When oven-dried or lyophilized samples were indicated, the moisture content used value was 15%. Samples of date syrup and wasted dates were also included since they usually possess similar TP content.

#### **3.3 Data cleaning**

*Antioxidants*

**2.2 The date palm fruit**

**3. Antioxidant in dates**

cism and casting doubt.

methanol extract."

variability or a manifestation of otherwise.

**3.1 The issue of large variability of total phenolic content**

Over the past two decades, several studies on antioxidant properties of date fruits have been published. These studies have contributed to increase our knowledge and understanding of these properties and the importance of dates as a food and its medical, therapeutical, and health virtues. However, the foresight of these studies finds great variations of levels and values of studied parameters of antioxidant of these results, which confuses the researcher/reader, leading to some skepti-

To illustrate the magnitude of the problem and the importance of attempting to overcome this wide disparity, I will review here what Hammouda et al. [17] recently noted while comparing their findings with results of a previous published. Hammouda et al. [18] estimated the TP of two date cultivars from three geographical origins using an HPLC methodology and reported an average of 154 mg/whole fruit (or 126.3 mg/edible part of the fruit, average weight of a fruit was 10.2 g). When they compared their findings with values reported on the widely cited study of Al-Farsi and Lee [6], which reported that TP ranged between 194 and 240 mg/100 g of fruit, corresponding to ~19–24 mg per fruit, they concluded that (a quote): "We consider that our estimation better reflects the real concentration of total polyphenols in dates as phloroglucinolysis−HPLC is the only quantification method that takes into account the nonextractable PCs which represent the major part of polyphenols in dates and which are not quantified when a colorimetric assay is performed on a

Many researchers have faced a similar situation and may have reached similar conclusions, as evidenced by many comparative studies. Recently, Mishra et al. [19] reviewed and analyzed the abnormalities associated with reporting the antioxidant activity using DPPH methods. Whether one agrees or disagrees with the above statement made by [18] is not the issue here. The issue is that whether the huge disparity of experimentally obtained and numerically reported values of antioxidants and antioxidant activity on date fruits really reflect the phenomena of natural

The date palm fruit, the date, is a berry or drupe consisting of a single inedible seed (pit) surrounded by a fibrous, parchment-like endocarp, a fleshy mesocarp, and the fruit skin (pericarp) [13, 15]. Usually, the fruit is oblong, though great variation exists in shape, size, color, as well as in quality and texture. Weight of dates ranges between 4 and 36 g; length, 2–7.5 cm; diameter, 1.3–4 cm; and volume, 5–19 cm. The edible part of the date represents 85–92% of the total fruit weight. The development of the date passes through five distinct morphological stages, widely known by their Arabic names: Hababouk (Habanbo), Kimri, Khalal (Besser), Rutab, and Tamer (**Figure 1**, **Table 1**). At full size, Khalal, the color of dates is either yellow or red, with different shading and hues, with the yellow-colored dates representing the majority (> 80%). Date maturation starts 10–15 weeks after pollination and takes place over an extended period lasting for about 6–8 months. This process requires developmental competence and high heat. Dates of some cultivars can be eaten starting from the Khalal stage; others can only be eaten during or after attaining some degree of ripening. Antioxidant properties of dates are directly and indirectly influenced by the physiological aspects and developmental stages (**Table 1**).

**104**

The name of the same date cultivar in different countries may have different spellings. An example of this is the cultivar Barhi which has the following synonymous: Berhi = Burhi = Barhee = Barhy; Deglet Nour = Deglet Noor; Sokary = Sukkari = Sukari; and Sofry = Sufry = Suffry. It was very essential for the analysis to designate a single spelling for the same cultivar.

Outliers were statistically detected and removed from analysis. Removing of statistically detected outliers, at this stage of analysis, was based on convenience, simplifying the analysis, to examine their effects on estimates. Their analysis requires a more rigorous methodology, and perhaps these extreme values may represent a reality.

#### **3.4 Statistical analysis**

Excel (Microsoft) and SPSS (IBM, version 23) were used for statistical analysis which included estimates of central tendency and variability.


**107**

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

**Parameter Stg. Mean** 

TF (mg/100 g DW) T 0.066 (0.094,

DPPH (IC50: ug/ml) T 17.43 (6.71,

TP (mg GAE/100 g DW) T 466.26 (66.54,

TF (mg RE/100 g DW) T 124.12 (53.06,

CT (mg CE/100 g DW) T 75.25 (11.86,

FRAP (umol TE/100 g DW) T 640.96 (157.8,

DPPH (IC50: mg/ml) T 3.94 (1.31,

ABTS (umol TE/100 g DW) T 621. 54 (124.8,

TP (mg GAE/100 g FW) T 246.67 (80.45,

TP (mg GAE/100 g DM) T 172.5 (56.84,

TP (mg GAE/100 g DW) T 216.22 (45.78,

TP (mg GAE/100 g DW) K 459.92 (62.89,

DPPH (IC50: mg/ml) K 0.59 (0.13,

TP (mg GAE/100 g FW) K 482.27 (93.14,

TF (mg CE/100 g DW) K 232.0 (53.91,

CT (mg CE/100 g DW) K 189.82 (68.66,

TP (mg GAE/100 g DW) T 2.68 (0.86,

**(SD, range)**

1.5–4.5)

0.01–0.38)

7.5–33)

331.9–537.1)

68.9–208.53)

57.6–92.1)

406.6–860.9)

2.1–6.2)

383.9–846.9)

134–343)

81–235)

141.9–297.0)

349–571.3)

0.47–0.86) R 1.06 (0.32, 0.75–0.98) T 1.86 (0.55, 1.4–2.9)

303.17–602.28)

109.79–307.59) R 144.49 (45.30, 79.6–231.0) T 94.81 (24.77, 52.8–140.5)

86.0–276.8) R 121.1 (46.57, 65.3–198.2) T 81.13 (22.24, 40.1–110.5)

R 362.93 (49.57, 278.8–435.4) T 269.96 (60.17, 182.2–375.5)

R 211.076 (55.08, 102.8–265.3) T 120.48 (47.46, 50.2–184.1)

**References**

[30]

[31]

[32]

[33]

[34]

[35]

[36] [37]

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

**(no. cultivar)**

2014 (13)

Bouhlali et al., 2017 (8)

**Country Author** 

Morocco Taouda et al.,

Oman Al-Farsi et al.,

Pakistan Nazeem et al.,

Tunisia El-Arem et al.,

2012, (4) El-Arem et al., 2013 (5)

2005 (3)

Singh et al., 2013 (6)

2011 (21)

Haider et al., 2013 (10)


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

*Antioxidants*

**Country Author** 

Algeria Benmeddour

Egypt Farag et al.,

Iran Biglari et al.,

KSA Farag et al.,

**(no. cultivar)**

et al., 2013 (10)

Mansouri et al., 2005 (7)

2014 (21)

2008 (8)

Mortazavi et al., 2015 (9)

2016 (18)

Hamad et al., 2015 (12)

Al-Turki et al., 2010 (5)

Hatem et al., 2018 (4)

TP (mg GAE/ 100 g DW)

**Parameter Stg. Mean** 

TP (mg GAE/100 g DW) T 493.15 (294.90;

TF T(mg QE/100 g DW) T 102.7 (94.45,

CT (mg CE/100 g DW) T 243.75 (139.62,

TP (mg GAE/100 g FW) T 4.70 (1.996,

TP (mg GAE/100 g DW) R 21.61 (45.27,

TF (mg CE/100 g DW) R 12.57 (26.18,

FRAP (umol/100 g DW) R 65.46 (121.79,

TEAC (umol TE/100 g DW) R 97.99 (152.43,

TP (mg GAE/100 g FW) K 126.04 (61.58,

TP (mg GAE/100 g DW) T 439.39 (559.37,

TP (mg GAE/100 g DW) T 17.52 (3.62,

TF (mg CE/100 g DW) T 2.12 (0.51,

TP (mg GAE/100 g FW) T 418.12 (55.18,

TP (mg GAE/100 g FW) K 4.92 (1.00,

DPPH (IC50: mg/ml) K 4.62 (0.36,

(Low) T 273.57 (40.53,

(Med) T 449.57 (115.42,

(High) T 1332.83

(Overall) T 638.48 (473.12,

**(SD, range)**

226–954)

15.2–299)

82.8–525.1)

2.5–8.4)

233–349)

437–622)

(271.06, 1100–1898)

233–1898)

2.4–141.4)

1.6–81.2)

11.6–387.3)

22.8–500.3)

57.8–262.8)

93–255)

10.5–22.1)

1.2–2.8)

315.68–508.01)

3.26–5.94)

4.1–5.1)

R 6.95 (2.63, 2.49–9.23)

T 6.15 (1.23, 4.25–7.65)

R 2.96 (1.53, 2.0–5.4)

T 4.0 (0.60, 3.4–5.0)

R 57.41 (20.47, 23.5–94.1) T 76.04 (18.87, 38.2–103.9)

**References**

[22]

[23]

[24]

[25]

[26]

[27]

[11]

[28]

[29]

**106**


### **Table 2.**

*Mean, SD, and range of selected parameters of antioxidant constituency (TP, TF, CT) and antioxidant activity (ABTS, DPPH, FRAP) extracted from selected published studies demonstrating the large reported variability.*


#### **Table 3.**

*Countries and number of recruited studies used to collect and analyze data points of TP content in date fruits.*
