Keywords

4.1 Date Palm

Date palm usually recognized as Phoenix dactylifera is considered as an ancient (5500–3000 BCE) cultured date crop that possess nutraceutical, economical and ornamental advantages. It is most commonly cultivated in arid and semi-arid areas worldwide because of religious, traditional, ecological, and social expansion of individuals present. Especially the Middle East and African countries are leading regions regarding date palm cultivation, production and export (Vayalil 2012). The fruit of date palm is generally considered as monocotyledonous and its tree usually found at a highness of 1500 m in well prepared drained loams. Currently, areas of many countries like Iraq, Iran, Saudi Arabia, Algeria, Egypt, Libya, Pakistan, Morocco, and Oman are famous for date palm cultivation. However, due to unique nutraceutical characteristics, date is consumed as major food item in numerous areas of Asian, Arabian, and various African countries (Assirey 2015). Date palm possess unique characteristic compared to other fruit crops due to its consumption at any of the various ripeness stages such as Rutab, Khalal and Tamar. It can be consumed both in fresh and dried form but on commercial level dried dates are mostly preferred because of their extensive shelf life. The ripening stages and choice of the varieties have a great influence on the sensory (taste, texture) nutritional and phytochemical properties that varies greatly in various regions. It was estimated that there are almost more than 5000 date varieties cultivated in various areas worldwide, among which Aseel, Dhakki, Zahidi, Majdool, Mabrook, Halawi, Lasht, Deggla and Bamy are considered as the most common ones (Khalid et al. 2016, 2017a, b).

4.2 Development of Date Pit as Value Added Product

There is a growing trend for cultivation of date palm across the globe due to increased utilization of date palms by the different food processing industries. Rising demands for dates and its products enhanced its production that touches to an amount of about 7.2 million tons in 2016, (Al-Alawi et al. 2017) and this accounts almost 720,000 tons of date seeds (10% of total datet palm). Moreover, about 1.3 billion tons of foodstuff and products waste formed annually all through the supply chain could fed almost two billion persons devoid of any detrimental effect on atmosphere as significantly recognized by FAO (Rodrigo et al. 2014). Nowadays, food waste is considered as “one of the great paradoxes of our times”, and it is the best deteriorating resources to bring into account for producing various other valuable food products. Various research studies demonstrated the use of different food industry waste in formulation of value added products and could also efficient source of economic profits for industry, farmers, food safety and product sustainability. In past, due to insufficient research on date pits, these are mostly used as feed for livestocks or as fertilizers. Today in modern times, extensive scientific research on date pits and their extracts make it possible to open up new avenues for its use. Modern scientific literature on date pits indicated wide range of applications in food, cosmetics and pharmaceutical products (Salah et al. 2012). For instance, date flesh and pits can be used to make nutritious granola bar that could be a great source of dietary fibers, antioxidants and other nutrients (Abu-Qaoud 2015; Ahmad et al. 2017).

Generally, the date palm fruit is comprising of fleshy pericarp and pit or seed (Fig. 4.1). Besides date flesh, seeds are recognized to possess high extractable value-added constituents. Various research studies on chemical composition of dates proved that pits are largely wasting byproducts of industries due to their biological and technological transformation. Consequently, a larger proportion of date palm pits might effortlessly be collected from various date based treating productions or by employing their wasted byproducts (Hossain et al. 2014; Khalid et al. 2017b).

Fig. 4.1
figure 1

Date palm and seed parts

Full size image

Date pits often underutilized and considered as low value agricultural by-products. Their actual potential was not discovered in last century, now it is considered as good source of nutritional components having vast applications in products formulation. For example, date pits are considered as a good precursor for the formulation of carbon, used as most popular and effective adsorbent in various industries (Yaish and Kumar 2015). It is also good in galactomannan, glucomannan and heteroxylan that had been extracted and characterized from date seeds. Ample amounts of carbohydrates (62.90%), crude fiber (19.99–39.66%) and lipids (7.87–9.76%) are also available in date pits. (Al-Humaid et al. 2010; Khalid et al. 2016). However, nowadays major consideration was given towards the lipids or oil extraction of date seeds due to their potential industrial and biological applications. Some studies demonstrated a diversified physiochemical configuration and fatty acid description in date pit oils. Date seeds oil was found to possess higher amounts of oleic acid (47.66%) and lauric acid 17.39%, however linoleic (10.54%), palmitic acid (10.20%) and myristic acid (10.06%) were also found in moderate to low levels (Elbasheer et al. 2012; Khalid et al. 2017a).

4.3 Nutritional Composition of Date Flesh and Pits

Date fruits and pits are recognized as enriched with various nutritional characteristics. The nutritive configuration of date palm flesh and pit has been described by various research studies. It was found that dates flesh and seed contains higher amounts of reducing sugars in addition to other amino acids, proteins and fats. Whereas, the date pits possess greater proportions of proteins, crude fat and crude fiber as compared to date flesh (Khalid et al. 2017a, b). Recent studied specified the proximate configuration of date flesh and pits and depicted the presence of moisture, ash, glucose, fructose, galactose and maltose, protein, fats and fibers in date pits and flesh. The details of these chemical constituents are as under:

4.3.1 Carbohydrates

Date fruits are considered as an energy dense food because of their rich carbohydrate constituents. Glucose and fructose are among the chief reducing sugars while sucrose as non-reducing and other polysaccharides such as starch and cellulose contribute as minor carbohydrate composition. The content of glucose, fructose and sucrose in date flesh varies and mainly depend upon date varieties, maturity stages and moisture contents. Studies suggested that date sugar content increases during Kimri, Khalal and Tamar stages, as the total soluble solids and sugars significantly increases with reduction in moisture levels (Abbès et al. 2011). Carbohydrate content gain special importance in date fruits as it is regarded as significant characteristic of both fresh and dried fruits on commercial basis. Sugar content comprises 50–80% of total date weight as 1 kg of dates provides 3000 calories. Dates are classified as sweeter or less sweet on basis of reducing or non-reducing content of dates. Comparing with date flesh, date seeds or pits comprises of almost 83.0% of carbohydrates among which, 42% of cellulose, 8% of hemicellulose, 25% of total sugar and other components are present (Ahmed and Theydan 2012). Date seeds signify almost 10–15% of total date fruit of which major contributors are insoluble fiber type carbohydrates (cellulose, hemicellulose). Similarly, carbohydrates are considered as major storage reservoirs in date seed endosperm mostly in (1 → 4) β-D mannan form. Several other hemicellulose portions that were recognized in date pits are mainly comprises of water-soluble gluco- and galacto-mannans and an alkali soluble heteroxylans. An alkali-soluble heteroxylans in date pits are generally comproses of xylose (82%) and 4-O-methylglucuronic acid (17%) with minor quantity of arabinoses and very few traces of galactose, glucose and mannose contents (Assirey 2015).

4.3.2 Dietary Fibers

Date palm kernel or seeds are good source of total, soluble and insoluble dietary fibers. Dietary fiber in date flesh can be characterized as insoluble fiber that comprises of cellulose, hemicellulose, lignocellulose, lignin, and insoluble proteins. Dietary fiber signify almost 6.4–11.5% of total date weight of which insoluble fiber ranges between 84% and 94%. However, the cellulose, hemicellulose, and lignin contribute 1.55%, 1.28%, and 2.01% of total date fiber, respectively (Breil et al. 2016). The nutritional constituents of date especially fiber greatly varies with different varieties and ripening stages. For example, the total fiber content of Deglet Nour is 8.09% and in Kentichi 20.25%. It significantly rises during kimri stage (6.1–12.3%) compared to the tamer stage (2.01–3.10%) of maturity. Not only date flesh but seeds are also regarded as excellent source of dietary fibers 77.8–80.2 g/100 g that constitute 10–20% of fresh date weight (Al-Daihan and Bhat 2012). The dietary fiber content of date pits has higher concentrations than date flesh. For example, Ajwa date palm has TDF constituents ranges between 6.20% and 8.70% while the Ajwa date pit has total dietary fiber of 26.4–33.9% (Khalid et al. 2017b). The various studies conducted on chemical analysis of dietary fiber demonstrates some important functional properties in food industry greatly associated with date fiber. For example: possession of higher water-binding capability, higher oil-holding capacity, emulsifying properties, pseudoplasticity behavior of suspensions, and gel formation. Moreover, to improve the nutraceutical properties in food products, dietary fiber can extensively be employed as an important constituent in many foodstuffs (dairy, soup, meat, bakery products and jams) generally recognized to alter texture related properties and enhance the high fat foods stability (Saafi-Ben Salah et al. 2012; Khalid et al. 2016).

4.3.3 Protein

The protein and fat contents of dates gain special importance due to their high concentrations and biological values. Dates provide almost 1–7% of total protein content and essential amino acids that play important role in human body. Date protein content deliver most important 16–20 types of amino acids, that are not even existing in fruits (orange, apples and banana) and other products. The most important amino acids present in date palm cultivars comprises of histidine, lysine, arginine, aspartic acid, threonine, glutamic acid, proline, glycine, alanine, cystine, valine, methionine, isoleucine, leucine, tyrosine, and phenylalanine (Samad et al. 2016). Moreover, dates isoleucine content is 800 times greater than apple and 5000 times greater lysine content than oranges. Not only date flesh but date seeds also contains considerable amount of protein constituent. Soluble proteins like albumin, globulin, prolamine and glutelin constitute main portion of date seeds that is 5–6% of total date proteins (Zhang et al. 2013).

Majority of essential and sulphur containing amino acids (methionine, cystine) comprises relatively considerable amount of date seed proteins compared to other seed protein products (soybean, peanuts, cottonseed). Glutamic acid, aspartic acid and arginine specified almost half of the total amino acids that are extracted from Ruzeiz and Sifri cultivars. Lysine is present in greater concentrations whereas the tryptophan is the only amino acid that is present in limited amounts in date seed fractions (Akasha et al. 2012). A brief composition of date flesh and pits are demonstrated in Table 4.1.

Table 4.1 Nutritional composition of date palms and pits
Full size table

4.3.4 Minerals and Vitamins

Dietary minerals are recognized as indispensable chemical constituents which are vital for numerous human functions like skeletal structure maintenance, cellular and biochemical reactions and functions. Hence the adequate amount of these minerals is necessary for optimum growth and maintenance of human physiological and metabolic functions. Regarding their importance dates fruit (flesh and pits) could highly considered as excellent sources of mineral constituents. Several studies reported that potassium content in date flesh of several varieties could be as higher as 0.9%. However, the most important minerals in date fruits are Ca, K, P and Mn (Kumar et al. 2014; Khalid et al. 2016). Dates are also preferred to various other fruits because of their high content of potassium, phosphorus and iron. Several studies demonstrated the higher percentage of iron content as compared to zinc and copper which is considerably present in lower amounts in date fruit. The beneficial fluorine content of date flesh has advantageous affects for preventing tooth decay. Similarly, selenium play important role in cancer prevention, providing antioxidant properties and improvement of human immune system (Sun et al. 2013). Date seeds are also found to be enriched with greater amounts of various minerals like Mg, Ca, P, Na, K, Al, Cd, S and Pb in various proportions. Additionally, in some of the varieties potassium contribute 0.5% of total date seed minerals. Whereas iron, manganese, zinc and copper confer major concentrations regarding micronutrients. Various studies stated that the major differences in the minerals content of date flesh and seeds are due to various date varieties, soil type and quantity of fertilizer. As the Saudi Arabian dates comprises of minor quantity of phosphorus ranges (0.19–0.26%) whereas the selenium component contribute 1.48–2.96 mg/g of total minerals proportion compared to other date varieties (Habib and Ibrahim 2009).

The important vitamins like vitamin A (exist as β- carotene or provitamin A), vitamin C (ascorbic acid), vitamin B1 (thiamine), niacin and riboflavin are reported in date fruits. Among various date cultivars Ajwa dates comprises of relatively high provitamin A and vitamin C content. Due to these important vitamin components, dates are regarded as an ideal food because they proposed important nutritional components with significant potential health benefits (Habib et al. 2014).

4.3.5 Lipids

The lipid contents are regarded as most important components of date’s fruits and gain special importance due to their nutritional significance. Although the date flesh comprises of only a small fraction of fat contents but date seeds are considered as much more concentrated source of lipids. Previous research studies demonstrated the narrow range of lipid contents in different date varieties but significantly varies along with maturity stages. For example the fat content generally declines from 0.5% to 0.1% from the Kimri to the Tamer maturity stages. The total lipid content in date seeds ranges from 5.05% to 12% while the oil contents that are 30–45% of total seed lipids have potential applications at industrial and pharmaceutical level (Al-Humaid et al. 2010; Akbari et al. 2012).

4.3.5.1 Free Fatty Acids

The most important fatty acids determined in date pits oil were comprising of oleic (C18:1), linoleic (C18:2), palmitic (C16:0), myristic (C14:0), and lauric (C12:0) acid that altogether contribute almost 90–95% of the total fatty acids. However, most of the fatty acids profile composition described in oil of the date pits may significantly differs among various varieties, and along with climatic and growing conditions (Amani et al. 2013). Similarly, among the major SFA (saturated fatty acids) possess by date–pits are: lauric acid (0.10–38.71 g), myrsitic acid (3.11–18.13 g), palmitic acid (0.41–15.19 g), and stearic acid (1.56–6.04 g) are present in greater concentrations. Likewise, palmitoleic acid (0.07–1.51 g) and oleic acids (32.15–54.10 g) are the chief MUFA (monounsaturated fatty acids) while linoleic acids (4.32–21.10 g) and linolenic acids (0.02–1.68 g) are the major PUFA (polyunsaturated fatty acids) but are present in relatively lower amounts (Akbari et al. 2012). Regarding the beneficial fatty acid profile, the date seed oil usually has low degree of unsaturation that exhibited good flavour and frying stability. Oleic acid in date pits as dominant component could considered advantageous to human health owing to its low saturated level and high potential to decrease LDL cholesterol along with greater oxidative constancy although the linoleic acid and linolenic acid is essential regarding growth of healthy human skin yet these posses less oxidative stability (Farooq et al. 2013).

4.3.5.2 Sterols

The studies based on GC analysis of date pits oil demonstrated the extraction of trimethylsilyl derivatives of sterols. The major sterol components determined comprises of cholesterol, campesterol, stigmasterol, β-sitosterol, avenasterol and stigmastadienl. Moreover, the β-sitosterol and campesterol were among the most important constituents of date seed oils that contribute almost 90% of total sterol fractions. Among which β-sitosterol add 83.31% and campesterol 9.10% of total sterols in seed oils. In some date varieties avenasterol is comparatively higher than other sterols e.g. Allig and Deglet Nour seed oil contains 4.50 against 0.45% of other sterols and greatly related with antioxidant effects (Al-Mssallem et al. 2013). Phytosterols was also found ranges from 0.50% to 0.90% for Allig and Deglet Noor varieties respectively. Phytosterols from date seed oils along with dietary fibers of date seed have a capacity to significantly lower the total and LDL cholesterol levels in hyperlipidemic individuals by preventing the intestinal cholesterol absorption. Despite this, date seed oil sterols can be highly beneficial for use as therapeutic agents for hypercholesterolemia treatments (Nigam and Singh 2011).

4.3.6 Antioxidant Compounds

4.3.6.1 Phenolic Contents

Date pits are considered as an excellent reservoirs of phenolics constituents (3112–4420 mg gallic acid) and antioxidants (570–919 μmol) (Ahmad et al. 2012). Various studies reported that comparing with various other edible oils (olive oil) date seed oils are regarded as rich source of phenolic contents (21–62 mg gallic acid) when extracted with numerous solvents (acetone–water, ethanol–water, methanol–water). Among several date varieties, Iranian date seeds had comparatively highest antioxidant and radical scavenging activity that could be employed for various pharmaceutical and commercial purposes (Suresh et al. 2013). Among various date seed phenolics gallic acid, protocatechuic acid, p-hydroxybenzoic acid, vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, m-coumaric acid and o-coumaric acid were recognized to be present in variable concentrations. While the hydroxybenzoic acid (9.89 mg), protocatechuic acid (8.84 mg), and m-coumaric acid (8.42 mg) were the phenolic constituents that contribute major antioxidant potential of date seeds (Waly et al. 2015).

4.3.6.2 Flavonoids

The flavonoids are regarded to be most abundant phenolic constituents present in date fruits. These polyphenols are mostly existing in date flesh with enormous health advantages such as antioxidant as well as radical scavenging activities. Due to antioxidant potential these phenolic compounds are operative in reducing cardiovascular and chronic diseases with positive response towards damaged cells proliferation. Date fruit is enriched with various flavonoids that mostly comprises of quercetin, isoquercetin, and rutin and can be determined using HPLC technique (Hossain et al. 2014; Kaleem et al. 2016). The various antioxidant flavonoids vary within different varieties same is true for date palm kernel or pits. However, the total flavonoids contents of Ajwa date palm is 2.79–4.35 mg/100 g whereas the date pit consists of 1.35–3.67 mg/100 g of quercetin content as predominant flavonoid. Similarly, the various amounts of these compounds significantly differ among pits and flesh of date fruits due to variations in genetic considerations, experimental situations, and hydration levels. Phytochemicals (phenolics and flavonoids) in date fruit have strong antioxidant potential and possess major health advantages like reducing diabetes, prevention of cancerous cells, and cardiovascular disorders. The therapeutic potential of date pits flavonoids is comparable to other fruits flavonoids in combating microbial and viral infections (Biglar et al. 2012; Ahmad et al. 2015; Khalid et al. 2017a).

4.4 Extraction of Lipids from Date Pits

There are different methods employed for lipid extraction from date pits either using different solvents like hexane and petroleum ether or by using microwave and ultrasonic extraction. However, solvent extraction methods consume more time with high usage of solvents. Modern technologies make use of techniques like microwave and ultrasound extraction for optimum extraction of lipids. Thus more beneficial in terms of time, cost reduction, solvent consumption and power effectiveness. These methods could also improve stability of compounds to be extracted, process simplification, and quality and quantity of extraction and extract respectively. The total lipids or oil extracted through these methods could possess better oxidative stability than most of the vegetable oils even used in comparison with olive oil. Due to its unique characteristics date pit oils possess wide variety of applications in pharmaceuticals, cosmetics, and food products (Jassim and Naji 2010). Some other methods used for lipids extraction of date pits are explained as follows:

4.4.1 Folch Method

Combination of various organic solvents have been suggested to use for extraction of lipids from date pits and other sources. Folch method is one of this kind of method based on extraction of fats by employing mix of solvents. Lipids from the endogenous cells are extracted using chloroform–methanol (2:1 by volume). In detail, the one-fourth of the saline solution was equilibrated with the normal homogenized cells with efficient mixing. The resulted mixture formed as a result of this combination was placed for some time for the separation of two layers and as a result lipids settled down in the top layer phase. This method was introduced in past for lipids extractions and after some modifications it formed the basics of all extraction procedures. The same procedure with some amendments is still employed for the assessment of date pits lipid extraction spectrophotometrically. Usually, the large number of samples are rapidly and easily processed by using this method. However, it lacks sensitivity in results in comparison with other modern processes (Ullah et al. 2011).

4.4.2 Bligh and Dyer Method

Bligh and Dyer method is another useful technique for lipid extraction and partitioning, protein exist at interface of two liquid phases in this technique. This method also have some similarity to Folch method, but the only difference is found between solvent-solvent and solvent-tissues ratio. During this process lipids from standardized cells suspension were extracted by employing 2:1 (v/v) methanol-chloroform (Breil et al. 2017). Then the desired lipids are extracted using chloroform phase and processed by numerous procedures. However, the above gravimetric method is most extensively employed by the date pits processors for lipids and oil estimation on commercial level. There are some basics improvements which have been made in order to modify this method. The major kind of modification is the prevention of acidic and denatured lipids binding by the addition of 1 M sodium chloride instead of water. Also the basic reason behind the preference of this method over others is that during lipid extraction from date pits, further addition of 0.2 M phosphoric acid and hydrochloric acid (Reis et al. 2013) to the NaCl solution resulted in progressive lipid recovery with very short time duration. Correspondingly, another kind of modification is the accumulation of 0.5% acetic acid to the water phase which significantly resulted in increased reclamation of acidic phospholipids. A more recent report suggested that such type of lipid extraction was verified to be the most proficient method for the date pits lipids extraction (Yao and Schaich 2015).

4.4.3 Ultrasonic-Assisted Extraction

The Ultrasound assisted extraction is considered as substitute to other lipid extraction methods, without problems that are associated with other conventional lipid extraction methods of cell disruption. This method is regarded as more simple that may result product of high purity. This technique offer an ecofriendly, economical, less time consuming, and product with greater quality. Comparatively, lower temperatures adopted in this technique ensure lower energy inputs (Chemat and Khan 2011). The ultrasonic waves generated in this process cause quick cycles of compression/decompression, resulted in the production of extremely confined power waves, that disrupts lipid containing cells in date pits. Sonication with high frequency waves resulted in cracking of cell membrane for lipids fractionation. The sonicators that are most commonly used during this process are hot and bath types that are most commonly employed for batch as well as for continuous operations. In the bath type processors, usually the shape and capacity of vessel determines the quantity and organization of transducers (Lee et al. 2012). The basic benefit related to this procedure as compared to microwave reactors is its formation and generation of low temperature and energy, thus resulted in less denaturation of heat sensitive lipid molecules. Additionally, the beads and chemical substances does not required to be excluded in the end time process that cast off additional cost. Though, extended sonication some time resulted in free radical formation, that may be detrimental to the extracted oil quality (Hosikian et al. 2010).

4.4.4 Microwave Extraction Method

Earlier, the microwave radiations applications were only restricted to samples digestion for estimation of metals and organic contaminants extraction. The microwave technology has greatly recognized as quick, safe and cost effective method for lipids extraction (Kim et al. 2012). In this method usually polar material or dielectric is introduced in electric field generated by microwaves, resulted in heat release due to various frictional forces among inter and intra molecular surfaces. During intracellular heating in this method, high energy water vapors formed, resulted in disruption of lipids containing cells, opening of cell membranes thereby intercellular lipid metabolites are extracted (Amarni and Kadi 2010). Consequently, the quick pressure and heating system generated within biological structure, forced compounds out from cell matrix, significantly resulted in best-quality extracts production along with recovery of better lipids compounds. It was suggested that microwave treated lipids cells of date pits possess greater oil yields, because of numerous cell wall cracks, resulted in extraction and transesterification of oils into biodiesels (Ghasemi et al. 2016).

The microwave extraction method is preferred compared to other methods because of its low equipment cost, less reaction time, small operating cost involved, and efficient extraction. This method is demonstrated to be more suitable for biodiesel recovery from reaction mixture in a very short time of 15–20 min, as compared to conventional time consuming (6–7 h) heating method. Conversely, the drawback associated with microwave method is the high cost involved on commercial level applications (Lee et al. 2010).

4.4.5 Nile Red Fluorescence Extraction of Lipids

The Nile red is considered as an intense fluorescent lipophilic dye highly employed to determine the intracellular lipids quantity in algae, selective novel herbs and date pits. Generally the efficiency of Nile red is effected by various cell membrane diffusion levels and greatly depends on the time required for highest fluorescence emission (Sitepu et al. 2012). Moreover, the Nile Red is recognized as the most appropriate method of oil extraction and estimation, highly used to determine the accumulated lipids through fluorescence microscopy after the accumulation of Nile Red in cellular lipids. This method is more easy, simple, modernized, efficient and preferred, that used fluorescence plate reader for lipids quantification and highly recognized for most of the lipids containing seeds including date pits, algae and yeasts (Rumin et al. 2015; Takeshita et al. 2015). Similarly, several studies demonstrated that this method provides more stable values by using 20% dimethyl sulfoxide during its growth phase. However, the fluorescence power capabilities highly reduced with enhancing dimethyl sulfoxide concentrations. This method demonstrated to added up more lipids fraction with passage of time using sodium chloride solution. Conversely, the penetration of Nile Red across the cell membrane highly depends on process conditions and type of cell for lipids extraction (Hounslow et al. 2017). Generally, the fluorometric process does required lipid to be extracted; but for the fluorometric dye penetration through the material is necessary. This method is also used for algal and yeast lipids extraction but for oilseeds like date pits, its efficiency is highly enhanced by adding dimethyl sulfoxide and Nile Red along with acetone (Natunen et al. 2015).

4.4.6 Expeller Press Oil Extraction

Expeller press is considered as one of the oldest and simplest oil extraction method from raw seeds. This conventional technique is equally effective in case of dried dates seeds (Demirbaş 2008). The oil extraction is proportional to higher mechanical pressure that is applied to date seeds mass to break down the cell structure, then to rupture them for lipid extraction. Higher extraction efficacy can only be achieved by applying pressure in a specific range, too much high pressure effect the lipids quality due to accumulation of high heat and also cause obstruction problems (Boldor et al. 2010). This technique can be combined with use of chemicals/solvents for enhanced recovery. The limitations with these extraction technique is the longer time of extraction and initial high costs. Additionally, for mechanical pressing, input material of low moisture content is desirable that require additional drying and thus incur extra energy and production costs (Ranjith et al. 2015). Another important drawback during date seed oil extraction is hindrance of oil due to rigid cell wall structure that is mostly not happens in most of the vegetables oil solvent extraction. By adopting mechanical expression process, several natural pigments also get their way into the crude oil that have to remove during refining process by using either solvent extraction or carbon adsorption method, that yet again responsible for additional cost. Other problems associated with this type of method comprises of higher energy and maintenance costs, skilled labors requirement, and less efficiency in comparison with other methods (Johnson and Wen 2009).

4.4.7 Bead Beating Extraction

Another mechanical method of cell disruption most commonly used is bead beating, where cell is directly damaged by high rated spinning of seed extract slurries along with quality beads. All cell types including date seeds could be processed by cell disruption using grinding beads opposite to seed cells. Moreover, due to usage of multiple shaking vessels in a bead mill with vibrant platform, such kind of bead extraction method is regarded as best for seed samples that required same handling settings for disruption. (Lee et al. 2012). However, improved oil extraction efficiencies could be acquired, when beads were agitated along with cell culture. The cooling jacket often used inside the mill to protect the heat sensitive cell molecules, and also to minimize the heat generated during entire process. Numerous types of beads are usually employed for varied cell categories, however the beads made up of zirconium oxide, or titanium carbide could significantly increase the distraction rates and extraction efficacy of date seeds probably due to their greater density and hardness (Šoštarič et al. 2012). The overall comparison of all lipids extraction methods is demonstrated in Table 4.2.

Table 4.2 Comparison of different methods for lipid extraction from date pits
Full size table

4.4.8 Superior Solvent Extraction Methods

In this type of solvent extraction method usually chloroform is used as the main lipid extracting solvent that enhances its effectiveness and efficiency. However, on commercial level during large-scale lipids extraction employing these procedures is excluded due to ecological and health threats. Consequently, many researchers have been developing the least-toxic, but more operative, alternatives such as by using ethanol, isopropanol, butanol, acetic acid esters, hexane, and numerous solvents in combinations for date pitsoil extraction (Sheng et al. 2011). Moreover, the usage of above described solvents highly dependent on the lipids classes required to be extracted. Though, in a latest research studies, the extracted lipid fraction was highly recovered by using 2-ethoxyethanol (2-EE) in comparison with other common solvent extraction methods (chloroform, methanol and hexane) (Jones et al. 2012). A general description of date pit oil extraction steps along with solvent fractionation is presented in Fig. 4.2.

Fig. 4.2
figure 2

Extraction method for date pit oil and bioactive substances

Full size image

To further improve the efficiency of extraction process, ASE (accelerated solvent extraction) process, employing heat and pressure, was introduced. This method highly shortens the extraction time, and thus resulted in efficient solvent recovery for re-usage, thus minimize the operating costs. Recently, most of the modern solvent extraction as well as combined solvent/physical extraction methods are being developed for lipid extraction by various researchers all over the world. Although, the organic solvent extraction methods have possess various disadvantages when executed on commercial level (Cooney et al. 2009).

4.4.9 Extraction of Lipids Classes

The better and efficient method was developed by (El-Sharnouby and Al-Eid 2009) for extraction of various lipid classes, that is a modified form of the Folch/Bligh and Dyer method. This procedure provides improved recovery of nearly all chief lipid classes and is based on using MTBE(Methyl-tert-butyl ether) as a solvent, and offers the most precise lipidemic profile. This can only be possible to acquire due to the development of a lipid-containing low density organic upper phase, that resulted in more easy and accurate lipid extractions. Briefly, 1.5 ml of methanol was mixed rigorously for 200 ml sample (vortexing), moreover after adding 5 ml of MTBE, the solution was incubated for 1 h at normal room temperature (Saura-Calixto 2012). Likewise, phase separation during the process was developed by the addition of 1.25 ml of water to the solution and permitted to stand at room temperature. The top organic phase was extracted by centrifugation and the lower phase was re-extracted by adding 2 ml of MTBE/methanol/water (10/3/2.5, v/v/v) to accomplish complete recovery of lipidic profile (Lemine et al. 2014). However, the excessive solvent remained could be easily drained off by vacuum drying of both the organic phases including lipid extract. Additionally, the resultant extracted lipids were retained for better storage by dissolving in 200 ml of chloroform/methanol/water (60/30/4.5, v/v/v) or can be directly employed for further studies (Mahmoud and El-Bana 2013). All these type of procedures are appropriate for lipid extraction from all kinds of lipid-bearing cells, containing date pits (El-Sohaimy and Hafez 2010).

4.4.10 Hydrolysis of Lipids by Supercritical Transesterification

Transesterification is recognized as an efficient method to make lipids extracts in the form of solid and liquid fractions. Generally, in this method wet lipids fractions from date seeds are processed for lipids extraction followed by trans esterification. Briefly, wet lipids mass was retained in stainless steel reactors, submerged in isothermic fluidized bath for specific time followed by water cooling process (Shin et al. 2014). Continuous hydrolysis reaction between two reactors carried out, followed by drying of pits extract and again mixed with water in huge reactors and the reaction was persistent for 1 h at 250 °C. Repeatedly continuous dehydration and drying process transforms the wet lipidic biomass into compact fraction, consequently the appropriate filters were used under light vacuum conditions for efficient separation of aqueous and solids phase (Han et al. 2011). Additionally, the detailed experimental procedure was carried out for the determination of special effects resulted by reaction time, temperature, ethanol filling yield and crude biodiesel configuration. Although, the resulted seed oil was checked to verify its quality characteristics to meet the standards by using appropriate methods. Yet, the described process has to be verified for its commercial utilization for date pits (Zhao and Zhang 2013).

4.4.11 Hexane: Isopropanol (HIP) Lipid Extraction

The hexane based lipid extraction method was used to quantify the lipid contents found in tissues using mixed solvent as hexane and isopropanol, followed by washing of extract and removal of non-lipid residues using sodium sulphate solution. Various studies demonstrated the use of HIP method was better and offer less residual level of solvents in final product. Gravimetric methods were usually recognized as best methods for the determination of lipids content weight directly, however the hexane-isopropanol was considered to be efficient for polar lipids extraction (Shimada et al. 2014). Moreover, the basic advantages of gravimetric methods are: total fat measurement, more quantitative process, least equipment requirements, less workers required, simpler and easier to accomplish. However, this method have several limitations including less accuracy of lipid weight, compositional analysis of fats, lowest detection level of lipids. This method require shorter time and resemble Folch method that required much shorter time for oil extraction as compared to gravimetric and soxhlet method (Murphy 2012).

4.5 Future Perspectives

Date seeds are considered as byproducts of various date fruit industries. Numerous studies demonstrated the potential of date seeds as a source of edible oil. In addition to oil, some other nutritional constituents like dietary fiber, protein, minerals, phenolic that present in significant amount make date seeds as an effective functional food ingredient. Hence the potential usage of date seeds in numerous industries is favorable for developing value added products. Having favorable lipids and fatty acid profile in date pits, it is recommended to use it for development of nutraceutical products, as an edible cooking oil, and for formulation of different oil based products (margarines), because of its higher oxidative stability and thermal resisting properties and have good shelf life capabilities for extensive storage time period. Furthermore, as date seed oil possess unique unsaturation degree in comparison to other vegetable oils, therefore highly recommended as a vegetable oil substitutes in many food industries.

Besides possessing wide variety of applications date seed offers great number of challenges. As there are less information regarding date seed oils, more research studies are required for determination of oil safety regarding its use as important constituent in pharmaceutical and food industry for the development of edible and non-edible products. Additionally, there is great need to meet the challenges of using suitable extraction methods from date seeds to attain the high oil production. Although date pits are also accessible at very low or without any cost, so the seed pits oil extraction could be possible and possess important worth considerations on commercial level. As the date seeds are recognized as discarded byproducts and have possess high probability to be used as ingredients for various food products formulation, for extraction of beneficial bioactive components, water sanitization, and biomass production. However, the future research studies require to be concentrated on technological development for commercialized production and biomaterials specification for their safety concerns and functionality needs. Presently the systematic health entitlements regarding date pits are at its initial stages so more research studies are requires for establishment of their safety and efficiency. Different studies were demonstrated to extract the date pits extract using numerous solvents, though it is more essential to improve more technological advancements for oil and other bioactive components extracted compounds to be employed for cosmetics, pharmaceutical and food products.

4.6 Conclusion

The various functional components of Date palm Phoenix dactylifera L., and pits described in this chapter constitute promising alternatives to various other crops as it is recognized an oldest plant and cultured for its desirable fruit and pits in various Arab countries for centuries and also preferred because of its nutraceutical and economical benefits. Compared to date flesh, pits are highly recognized as an important source of dietary carbohydrates, proteins, fibers, antioxidant compounds, definite indispensable vitamins and minerals. Especially the lipid fraction of date pits constitute major portion along with higher amounts of beneficial oleic acid and lauric acid, however linoleic acid, palmitic acid and myristic acid were present in lower amounts respectively. The different extraction methods described here establish favorable alternates to recover date pit lipid fraction either using different solvents like hexane and petroleum ether or by using microwave and ultrasonic extraction. However, solvent extraction methods are less prefer because of excessive time consumption and usage of greater amount of solvents. Also the basic reason behind the less usage of organic solvents for oil extraction is highly related to the harmful effects associated with these compounds. Consequently, various type of modern technologies like microwave, expeller pressing and ultrasound extraction provide more benefits in terms of time and cost reduction, solvent consumption and power effectively. These methods could also improve stability of compounds to be extracted, process simplification, and quality and quantity of extraction and extract respectively.

An important drawback in the research studies of date oil extraction is the process scale-up, comprising the process cost and efficiency analysis. The most of the research studies regarding oil extraction from date seeds have been accomplished on lab scale. That out comes about a very little information regarding availability and development of this process on large scale. Consequently, additional studies should be conducted using greater amounts of date seeds biomass to analyses the oil extraction efficacy and to compared with results studies previously identified for lab-scale process.