The Antioxidant Power of an Algerian Dry Date Variety Phoenix dactylifera L. ^†

Abstract

The date palm (Phoenix dactylifera L.), which is the pivot of oasian agriculture, offers a range of agricultural by-products, which remain very poorly exploited and are still used in a traditional way in animal rations. Date waste or dry dates are the result of sorting after harvest, accounting for 25% of annual date production. This co-product of poor quality and low market value has been shown to be rich in various secondary metabolites endowed with antioxidant and anti-radical properties. In order to make the most of Algerian oasian flora, a potential source of bioactive natural molecules, a chemical and biological study of three parts of the fruit of the Phoenix dactylifera plant (‘N’ stone, ‘P’ pulp and ‘N + P’ whole dates) was carried out. The bioactivities of hydro-methanolic extracts were assessed by determining antioxidant activity. The date pulp ‘P’ showed better anti-free radical activity with the DPPH test (p < 0.01). The bioactive substances isolated in the stone fractions ‘N’ showed excellent antioxidant activity with the ABTS test (p < 0.05). Moreover, the raw extract of N showed excellent antioxidant activity superior to that of the standard BHT with the CUPRAC test (p < 0.001). The fruits of Phoenix dactylifera and mainly the stones ‘N’ have excellent antioxidant activity and abundant secondary metabolites, which could provide corroborating evidence in terms of the potential elimination of free radicals from the fruit.

1. Introduction

The fruit of the date palm (Phoenix dactylifera), usually called date, is a species in the family Arecaceae that is rich in many essential nutrients and polyphenols, and it is one of the most consumed fruits in the Middle East and North Africa [1]. The Algerian Sahara, the heart of the country, extending over three quarters of the total surface area, with its rich heritage in date palms, allows the country to occupy the position as the fourth largest world producer of dates with 789,357 tons and the first largest producer of the Union of the Arab Maghreb [2]. The Algerian production of date trees consists of over 13 million palm trees and 940 cultivars [3]. The palm fruit is a source of high-value nutrients, rich in primary metabolites such as carbohydrates, proteins, dietary fibre, minerals and the vitamin B complex [4]. Dates are also considered a good source of phytochemicals or secondary metabolites such as antioxidant vitamins A, C and E, along with anthocyanins, isoquercetrin, quercetin, procyanidins, apigenin, luteolin and rutin, with a significant content of polyphenols and flavonoids in the fruit of the date palm [5]. Phytochemical research claims that dates contain bioactive phytochemicals that give them pharmacological properties. The fruit of the date palm has a free radical scavenger, so it has antioxidant power. Phoenix dactylifera L. benefits from antimutagenic, antimicrobial, anti-inflammatory and gastroprotective properties. This fruit has hepatoprotective, nephroprotective, anti-cancer and immunostimulating activities [6]. In addition to the food use of dates, these date palm co-products have important medicinal value and are widely used to treat a variety of diseases in various traditional systems of medicine [7]. In order to enhance Algerian oasian flora, a potential source of natural bioactive molecules, we conduct our present work, which aims to deepen the knowledge on the botanical species Phoenix dactylifera L. that has great pharmacodynamic properties. For this, we set the main objectives as the phytochemical screening and in vitro evaluation of the antioxidant activity of the hydro-methanolic raw extracts of the three parts (pulp ‘P’, stone ‘N’ and date ‘N + P’) of the fruit Phoenix dactylifera L. variety “Hachef”.

2. Materials and Methods

After the harvest of fruit from palm groves in the Oued-Souf region (Algeria), dates were dried, crushed and pressed according to the AOAC method [8]. In the Pharmacological and Toxicological laboratory in Veterinary Science Institute (LURPHATOX), liquid–solid extraction and phytochemical screening were performed to evaluate the secondary metabolites responsible for antioxidant activity. The antioxidant activity of extracts of randomly collected dates was evaluated and compared using spectrophotometric methods: methods for determining the oxidation of radical 2,2-diphenyl-1-picrylhydrazyl (DPPH) [9], the trapping activity of the radical cation ABTS (2,20-azinobis[3-ethylbenzothiazoline-6-sulfonate]) [10] and the reduction of the copper–neocuproine complex (CUPRAC) (Cupric ion Reducing Antioxidant Capacity). This was represented by the 50% inhibitory concentration (IC₅₀ and A_0.50) [11]. The synthetic antioxidants butylated hydroxyltoluene (BHT) and Butylhydroxyanisole (BHA) were used as a positive control.

3. Results and Discussion

Based on the results of the antioxidant activity of the hydro-methanolic extracts of fruit Phoenix dactylifera (

Table 1. Antioxidant activity of hydro-methanolic extracts of fruit Phoenix dactylifera measured by DPPH, ABTS and CUPRAC (mean ± SEM).

Phoenix dactylifera		Inhibition Rate (IC50, A0.50 μg/mL)			p
		DPPH	ABTS	CUPRAC
Date (P + N)		8.20 ± 0.69 *	24 ± 0.69	27.46 ± 1.94	<0.001
Pulp (P)		4.24 ± 1.60 ***	17 ± 1.60	46.80 ± 1.11
Stone (N)		12.15 ± 1.56	12.86 ± 1.56 *	1.82 ± 1.56 ***
Controls	BHT	6.82 ± 0.49	1.29 ± 0.03	8.97 ±0.87
	BHA	6.14 ± 0.49	1.81 ± 0.10	5.35 ± 0.19

P + N: whole dry date; P: dry date pulp; N: date stones; BHA: Butylhydroxyanisole; BHT: Butylhydroxytoluene; A_0.50; IC₅₀: inhibitory concentration at 50% of activity; * Significant difference (p < 0.05). *** Very high significant difference (p < 0.001).

), we found that the P extract has strong and excellent antioxidant activity (CI₅₀ = 4.24 ± 1.60 μg/mL; p < 0.001) higher than that of the two standards studied.

Moreover, it is noted that the best free radical trapping capacity (ABTS) is represented by extract N (IC₅₀ = 12.86 ± 1.56 µg/mL; p < 0.05). The reduction of the copper–neocuproine complex (CUPRAC) showed that extract N has excellent copper-neocuproine complex reduction activity compared to standard BHA (A_0.50 = 1.82 ± 1.56 vs. 5.35 ± 0.19 μg/mL; p < 0.001).

The results were in line with those of Ahmed and Rocha [12] who reported that date fruits exhibited potent DPPH scavenging capacities. This antioxidant activity could be due to the high content of the phytochemical compounds present in the fruit [5]. The ABTS radical scavenging activity of the hydro-methanolic extract of the fruit of Phoenix dactylifera was concentration-dependent. The increasing scavenging activity of the aqueous extract on an ABTS radical with increasing concentration could be attributed to the presence of antioxidants, especially phenols such as flavonoids [13].

4. Conclusions

From the results obtained in this study, it can be deduced that the hydro-methanolic extract of the fruit of Phoenix dactylifera possesses antioxidant properties, which is evident from its free radical scavenging activities against the free radicals used and also from the presence of some phytochemicals such as flavonoids known to possess antioxidant potentials.