Antioxidant Properties and Health Benefits of Date Seeds

Moran Brouk and Ayelet Fishman

16.1    Introduction

The date palm (Phoenix dactylifera L.) is considered a symbol of life in the desert because it tolerates high temperatures, drought, and salinity more than many other fruit crop plant species. It is one of the oldest trees from which man has derived benefits, and it has been cultivated since ancient times. Remains of dates have been found on a number of Neolithic sites, particularly in Syria and Egypt suggesting that they were being eaten by man as much as 7000–8000 years ago (Morton 1987; El-Juhany 2010). The world production of dates is 7.9 million tons per year with Egypt, Iran, and Saudi Arabia being the largest producers (FAOSTAT 2010).

For thousands of years, the fruits (dates) of the date palm were consumed as a staple food and believed to have remarkable nutritional, health, and economic value (Al-Shahib and Marshall 2003; Mansouri et al. 2005; Al-Farsi and Lee 2008a; Rock et al. 2009). Dates provide a good source of energy (213 and 314 kcal/100 g—fresh and dried respectively) mostly due to the high carbohydrate content, averaging 54.9 and 80.6 g/100 g for fresh and dried fruit, respectively (Al-Farsi and Lee 2008a).

In addition to numerous evidence regarding the valuable antioxidant and anti-mutagenic properties of the date palm fruit (Vayalil 2002; Mansouri et al. 2005; Hong et al. 2006; Rock et al. 2009), recent studies indicate that the seeds of dates also possess high levels of phenolics, antioxidants, and dietary fiber, even higher than those present in the date flesh (Hamada et al. 2002; Al-Farsi et al. 2007). This review focuses on the antioxidant properties and health benefits of date seeds and describes a new coffee-substitute drink based on date seeds.

16.1.1    Composition of Date Seeds

It is estimated that the date seeds constitute approximately 10 % w/w of the total weight of the ripe date fruit (Hamada et al. 2002; Habib and Ibrahim 2011). The seed composition depends on the variety but contains approximately 8–10 % moisture, 4.0–5.6 % protein, 6.0–8.5 % oil, 1 % ash, and 75–81 % carbohydrates including soluble sugars and mainly dietary fibers (Devshony et al. 1992; Besbes et al.

2004b; Al-Farsi et al. 2007; Nehdi et al. 2010; Al Juhaimi et al. 2012). The soluble sugars comprise glucose, fructose, raffinose, stachyose, sucrose, and galactose in average concentrations of 3.5, 3.8, 3.2, 3.7, 3.5, and 2.2 g/kg respectively (Al Juhaimi et al. 2012). Date seeds are rich in potassium 350–400 mg/100 g, phosphorus 200 mg/100 g, magnesium 70 mg/100 g, and calcium 40 mg/100 g and to a smaller extent iron—10–20 mg/100 g (Al-Shahib and Marshall 2003; Nehdi et al.

2010; Al Juhaimi et al. 2012).

At room temperature, the seed oil is a yellow liquid having a refractive index of

1.456 (Nehdi et al. 2010). Carotenoids present in substantial amounts (5.5 mg/100 g oil) are responsible for the visible color measured at 420–470 nm (Nehdi et al.

2010). The fatty acid composition of date seed oil comprises nearly 50 % of monounsaturated fatty acids primarily due to the abundance of oleic acid. Saturated fatty acids account for 40 % with lauric (C12:0, 18 %), myristic (C14:0, 10 %), and palmitic (C16:0, 12 %) being the most plentiful, and linoleic acid (C18:2) accounts for the remaining 10 % (Besbes et al. 2004b; Saafi et al. 2008; Al Juhaimi et al. 2012). These values can slightly change depending on the cultivar, with the Allig brand for example, containing only 27 % saturated fatty acids and 23 % polyunsaturated fatty acids (Besbes et al. 2004b).

Sterols comprise the main unsaponifiable fraction in date seed oil with a level of

300–350 mg/100 g oil (Nehdi et al. 2010). Differences in sterol composition make them suitable for determining the botanical origin of oils and hence detecting adul- teration. The major sterol in date seed oil is β-sitosterol (75 %) followed by campes- terol and Δ5-avenasterol (10 % each) similarly to few other vegetable oils such as olive oil and grape seed oil (Besbes et al. 2004a). Date seed oil contains 50 mg of tocopherols and tocotrienols per 100 mg of oil (Nehdi et al. 2010) with a profile similar to palm oil (Besbes et al. 2004a). The major tocols are α-tocotrienol, γ-tocopherol, and γ-tocotrienol at 34.01, 10.30, and 4.63 mg/100 g, respectively. These compounds possess antioxidant properties and they are active as vitamin E, albeit to different extents, making them particularly important for human health.

In recent years phenolic antioxidants have received increasing attention due to their beneficial effects on human health and their high potential in preventing a variety of pathologies such as cardiovascular diseases, diabetes, and cancer (Crozier et al. 2009). Their antioxidant activity is attributed to their ability to donate a hydro- gen or electron and delocalize the unpaired electron within the aromatic structure (Fernandez-Panchon et al. 2008). Phenolic antioxidants are widely distributed in the plant kingdom and thus in a wide variety of food products including dates (Fernandez-Panchon et al. 2008; Saafi et al. 2009). Indication of the total phenolic

content in a sample can be provided by the Folin-Ciocalteu method. This method is an electron transfer-based assay which measures the reducing capacity of a solution, and has been correlated with phenolic content (Prior et al. 2005). Al Farsi and Lee (Al-Farsi and Lee 2008b) examined the phenol content of Mabseeli date seeds grown in Oman and a level as high as 184 mg ferulic acid equivalents/100 g wet weight was obtained depending on the extraction solvent (water vs. 50 % acetone) and on experimental parameters such as temperature, solvent/seed ratio, and num- ber of extraction cycles. In a different study, levels of 3102–4430 mg gallic acid equivalents/100 g fresh weight were reported for three varieties (Al-Farsi et al.

2007). Various factors such as variety, growing conditions, maturity, season, geo- graphic origin, fertilizer, soil type, storage conditions, and amount of sunlight received, among others, might be responsible for the observed differences, as well as experimental protocols (Al-Farsi et al. 2007). The specific phenolic compounds identified using high performance liquid chromatography (HPLC) are hydroxylated derivatives of benzoic acid (gallic acid, protocatechuic acid, p-hydroxybenzoic acid, and vanillic acid) and cinnamic acid derivatives (caffeic acid, p-coumaric acid, feru- lic acid, m-coumaric, and o-coumaric acid) (Al-Farsi and Lee 2008b). Compounds typical of olives such as tyrosol, hydroxytyrosol, and oleuropein were also reported (Besbes et al. 2004a). The oxygen radical scavenging capacity (ORAC) values give an indication of the ability of different compounds to scavenge oxygen radicals in vitro which is a true measure of antioxidant performance, through a hydrogen atom transfer reaction mechanism (Prior et al. 2005). While the exact relationship between the ORAC value of a food and its health benefit has not been established, it is believed that foods higher on the ORAC scale will more effectively neutralize free radicals in biological systems as well. Al-Farsi and co-workers reported values of 580–929 and 146–162 Trolox equivalents per gram fresh weight for date seeds and date fruits, respectively (Al-Farsi et al. 2007).

16.2    Health Attributes of Date Seeds

According to the free-radical theory of aging, foods containing antioxidants such as vitamins or polyphenolic compounds will slow the oxidative processes and free- radical damage that can contribute to age-related degeneration and disease (Manach et al. 2004; Fernandez-Panchon et al. 2008). Recent studies show that date fruit consumption (and mainly the Hallawi variety) by healthy subjects, confers benefi- cial effects on serum triacylglycerol and oxidative stress and does not worsen serum glucose and lipid/lipoprotein patterns, and thus can be considered an anti-atherogenic nutrient (Rock et al. 2009). Owing to their high level of antioxidants (Al-Farsi et al.

2007), date seeds were also examined recently for their health benefits. Male rats were fed a basal diet containing 0, 70 or 140 g/kg date seeds for 30 days (Habib and Ibrahim 2011). Indication of oxidative damage was assessed in the liver and serum, and antioxidant status was assessed in the liver. The results showed that date seeds

significantly reduced liver and serum malondialdehyde (a lipid peroxidative damage product)  and  serum  lactate  dehydrogenase  and  creatine  kinase.  The  levels  of α-tocopherol, ascorbic acid, and glutathione and the activities of catalase, glutathi- one peroxidase, and superoxide dismutase in the liver were not altered by dietary treatments. Blood counts and serum biochemical parameters were not altered as well. Therefore, Habib and Ibrahim concluded that the results obtained suggest a protective effect of date seeds against in vivo oxidative damage, possibly through the action of their bioactive antioxidants (Habib and Ibrahim 2011).

Ben Abdallah et al. investigated the effects of date seed oil on epididymal sperm characteristics, testicular antioxidant enzyme activities, and testicular lipid peroxi- dation in male mice treated with different doses by intraperitoneal route for 4 weeks (Ben Abdallah et al. 2009). They found a significant increase in sperm count, motil- ity, and viability in all treated animal groups in comparison with the control group. In addition, the percentage of abnormal sperm was significantly lower in the treated groups. In a subsequent study, the researchers evaluated the effect of date seed oil on human male spermatozoa under induced hydrogen peroxide stress conditions (Ben Abdullah et al. 2009). Results showed that incubation with H2O2 alone led to a significant increase in lipid peroxidation (57.83 %) associated with a significant decrease in sperm motility, sperm viability, and percentage of reacted acrosome. Date seed oil improved sperm motility and protected spermatozoa against the dele- terious effects of H2O2 on motility, viability, acrosome reaction, and lipid peroxida- tion. Human epidermal keratinocytes were also shown to be protected against H2O2-induced stress by date seed oil (Dammak et al. 2010).

16.3    Uses of Date Seeds in Food

16.3.1    Bread Enrichment

Derived from the growing world production and consumption of dates, the amount of date seeds is also growing rapidly. This waste product of the date industry is typi- cally discarded or used as fodder for animals (Hamada et al. 2002; Besbes et al.

2004a; Al-Farsi and Lee 2008b). Potential uses of date seed oil are the cosmetics and pharmaceutical industries especially in light of the recent promising in vivo and in vitro results in animals and human (Ben Abdallah et al. 2009; Ben Abdullah et al.

2009; Dammak et al. 2010). With respect to usage in food, date seed milled into coarse powder was incorporated into Saudi Mafrood flat bread at 0, 5, 10, and 15 % replacement levels in comparison to wheat bran (Almana and Mahmoud 1994). Breads containing milled date seed fractions were slightly lower in protein and slightly higher in fat but substantially higher in total and soluble dietary fiber than the control bread. Coarse fraction at 10 % replacement level was found to increase the total dietary fiber contents in bread by fourfold without a significant adverse effect on bread quality. Wheat bran at the same level of replacement increased

the total dietary fiber content in bread by only threefold. Furthermore, breads containing 10 % milled coarse fraction were better or similar to the corresponding wheat bran control in sensory evaluation (Almana and Mahmoud 1994).

16.3.2    Coffee-Substitute Hot Beverages

By roasting and grinding date seeds, they can be exploited for the preparation of hot beverages as coffee-like brew. Such a drink, made of roasted date seeds, has been traditionally consumed in the Arabic world (Rahman et al. 2007). With the growing awareness regarding health foods and functional foods, coffee-substitute drinks which can provide a high antioxidant content accompanied by low caffeine intake are of public interest. Recently, a commercial date seed-based hot beverage marketed by the brand name Espressodate® was launched in Israel. This date-based coffee is prepared from roasted and grinded date seeds, blended with 5 % coffee beans and sugar, and commercialized either as instant or espresso coffee. We analyzed this drink on a serving cup basis in order to evaluate the actual consumption of antioxi- dants by consumers in comparison to coffee (Table 16.1).

Table 16.1  Total phenolic content and oxygen radical scavenging capacity (ORAC) of hot beverages

 

Method of preparation	Sample	Total phenolicsa	ORAC valuesb
Suspension in hot water	Espressodatec	4.5 ± 0.16	17 ± 2
	Black grounded coffee	9.1 ± 0.8	24 ± 0.4
	Espressodate with 10 % unroasted Majul seeds	7.72 ± 0.07	23 ± 2
	Unroasted Majul seeds	16 ± 3	38 ± 4
Espresso machine	Espressodate	10.5 ± 0.02	35 ± 3
	Espresso coffee	39 ± 4	75 ± 5
	Espressodate with 10 % unroasted Majul seeds	20 ± 2	44 ± 1
Filter preparation	Filter drink from Espressodate	2.28 ± 0.04	11 ± 0.6
	Filter drink from Espressodate with 40 % unroasted Majul seeds	7.4 ± 0.1	19 ± 2
Soluble instant coffee	Taster’s choice	5.3 ± 0.4	21 ± 0.4
Instant coffee substitutes	Chicory based	1.31 ± 0.03	2.1 ± 0.1
	Organic barley	3.3 ± 0.1	10 ± 0.8
	Decaffeinated instant coffee	5.4 ± 0.05	20 ± 1

Standard deviations are presented for experiments which were performed in duplicates or tripli- cates

aMeasured by the Folin-Ciocalteu assay and expressed as gallic acid equivalents (mM)

bOxygen radical scavenging capacity expressed as mM Trolox equivalents

cEspressodate is a commercial drink made from roasted date seeds with 5 % coffee beans

The Folin-Ciocalteu values of the date seed-based hot beverages ranged from

2.28 ± 0.04 to 20 ± 2 mM gallic acid equivalents, depending on the sample prepara- tion procedure (Table 16.1). The results indicated that date seed beverage made with an espresso machine contains more phenols than a hot water suspension and more than filter brew. The content decreases from 10.5 > 4.5 > 2.28 mM gallic acid equiva- lents. This is despite the fact that the amount of coffee powder used for preparation is in the opposite order (14 g for espresso, 20 g for hot water-based date coffee, 16 g for filter brew). Apparently, the espresso machine extracts more antioxidants than just hot water or a filter process. In addition, from the results it is evident that date seed coffee substitute contains less phenolics than coffee. The amount is only 50 % when the coffee is prepared using hot water (4.5 ± 0.16 vs. 9.1 ± 0.8), and 27 % for espresso preparation. However, comparing to soluble instant coffee (Taster’s Choice®) the values are similar. Moreover, other coffee substitutes, as chicory and organic instant barley, contain only 29 % and 73 % phenolics, respectively, relative to that of date seed beverage prepared by suspending in hot water.

It was suggested that the phenolic content declines during the roasting process of the seeds. This was confirmed by extracting unroasted seeds with hot water in a similar way to the date drink (Table 16.1). The unroasted Majul seeds contained

16 ± 3 mM gallic acid equivalents compared to 4.5 ± 0.16 for date seed coffee sub- stitute in hot water. Therefore, unroasted seeds were added to the date seed drink in order to evaluate if there is an overall improvement in phenolic content. In most cases, especially for the espresso machine-derived drink and filter preparation, the phenolic content indeed improved.

The total phenolic compounds of ready-to-drink orange juice and nectar was evaluated and reported to range from 18.7 to 54.2 mg of gallic acid per 100 mL beverage (Stella et al. 2011). Orange juice is considered by the consumers as a healthy beverage, providing a good source of antioxidants. Nevertheless, the phenolic contents of the juice drinks tested were lower than those obtained for the Espressodate beverages (the orange juice Folin-Ciocalteu values correspond to

1.1–3.2 mM gallic acid equivalents).

The ORAC values presented in Table 16.1 correspond well with the total phenol content. Espressodate beverage prepared with an espresso machine exhibited higher activity than hot water extraction or using a filter method. This is the same order of activity  obtained  for  the  Folin-Ciocalteu  method:  espresso > hot  water > filter. Likewise, black grounded coffee has higher ORAC values than date seed coffee substitute (1.4-fold), similarly to the Folin-Ciocalteu values (twofold). Moreover, the unroasted seeds showed a significant level of ORAC values. Adding unroasted seeds to date seed beverages prepared in different methods resulted in a moderate increase in ORAC values.

Identification of specific antioxidants in the date seed-based hot beverages using HPLC-mass spectra analysis revealed the presence of several polyphenols similar to those found in the date fruits by Mansouri et al. (Mansouri et al. 2005). Among these polyphenols are the sinapic acid and hydrocaffeic acid. In addition, the pres- ence of cinammic and caffeic acid derivatives was detected together with small amounts of protocatechuic acid, which was previously reported in oils extracted from date seeds (Besbes et al. 2004a).

 

16.4    Conclusions

Date seeds contain significant amounts of beneficial food ingredients such as oleic acid, dietary fibers, and polyphenols. These compounds have been associated with reduced incidence of cardiovascular diseases and improved overall well-being. Date seeds have been recently exploited for production of staple foods such as bread and hot beverages without impairment to sensory characteristics. Using an undesired by-product of the date industry as a raw material for functional foods has great economic potential and is thus expected to grow in the coming years.

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