Keywords

1 Introduction

Human beings use fruits as the main source of food. Researchers have reported that dry and fresh fruits can be used for the medical purpose as well as food (Marwat et al. 2009). Such studies arouse great enthusiasm among researchers and food companies to produce new varietal products and extract bioactive compounds from natural fruits that can have positive effects on human life (Viuda-Martos et al. 2010). Consumers use unprocessed or raw food and fruit juices to obtain rapid energy supply as well as maintain minerals quantity in the body.

Pomegranate (Punica granatum L. ) is the oldest holy fruit and considered as “jewel of winter”, belongs to the Punicaceae family. It follows the Latin name of the fruit Malum granatum, which means “grainy apple (Fig. 37.1). Pomegranate is native to India, Iran and its cultivation stretching all the way to the entire Mediterranean and Southwest American regions since ancient times (Celik et al. 2009; Lansky and Newman 2007). Current world production is estimated around 3.5 million ton per annum (Sinha et al. 2016). The leading producers of pomegranate are India, Iran, China and USA (Holland et al. 2008). In Pakistan pomegranate is harvested in the month of August to October in geographical locations of Gilgit Baltistan, Waziristan, Kurram agency, Dir, Chitral, Hazara, west of Baluchistan and Azad Kashmir. Table 37.1 shows the composition of pomegranate seed.

Fig. 37.1 
figure 1

Pomegranate plant, flower, fruit and oil

Full size image
Table 37.1 Proximate composition of pomegranate seed
Full size table

The pomegranate plant is widely considering as large shrub or small tree (~5 m), mostly grown in hot and dry and in humidity and dry season to get produce high-quality fruit with good yield. The fruit of the pomegranate is considered as a large berry and can be divided into three parts (seed, juice and peel). The pomegranate fruit contains multi-ovule chambers (8–12) which are separated by fleshy mesocarp and membranous walls. The chambers are packed with numerous seeds (arils) and enveloped by a transparent juicy layer. Depending on the variety, the size of arils, the hardness of seed and color of the juicy layer can differ from deep red to white (Holland et al. 2009).

Approximately 3% of the fruit weight contains seed, 30% juice and rest is the peel, including interior membranes (Lansky and Newman 2007). Over hundreds of years, pomegranate has accompanied mankind as a symbol of longevity, life, morality, health, knowledge, and spirituality (Mackler et al. 2013). Table 37.2 shows the main components present in different parts of the pomegranate tree and fruit.

Table 37.2 Major components of pomegranate tree and fruit
Full size table

2 Types and Varieties of Pomegranates

Several varieties of pomegranates (~500) with different size, varying shapes, taste and color are cultivated throughout the world. Fruits are round, obvate in shape and vary in diameter from 8 to 12 cm. The rind may be thick or thin and the color ranges from pale yellow to crimson. The pulp in superior types is thick, fleshy and very juicy, while in inferior types it is thin (Fig. 37.1).

The seed coat varies in hardness, some of the softer seeded types known as seedless. There is a number of seedling verities of pomegranate available. Selecting a variety with known qualities is always the better choice. Most horticulturists divide pomegranate verities into three categories sweet, sweet-tart and sour. Hiwale (2009) divided pomegranate into six groups based on the hardiness of the seed.

  1. 1.

    Soft seeded sweet

  2. 2.

    Soft seeded tart

  3. 3.

    Early variety (mostly sweet)

  4. 4.

    Normal (harder) seeded sweet tart

  5. 5.

    Normal (harder) seeded sweet

  6. 6.

    Sour (nearly always normal seeded)

3 Chemical Composition of Pomegranates

The constituents present in pomegranate fruits vary due to climate, region, cultivation, maturity and environment of storage (Barzegar et al. 2004; Fadavi et al. 2005; Poyrazoğlu et al. 2002). Different researchers have reported variations in fatty and organic acids, sugar, phenolic compounds, minerals, and water-soluble vitamins in pomegranate (Aviram et al. 2000; Çam et al. 2009; Davidson et al. 2009; Mirdehghan and Rahemi 2007; Tezcan et al. 2009). Around 50% weight of pomegranate fruit consist of the peel. It has many significant bioactive compounds including phenolics, ellagitannins (ETs), flavonoids and anthocyanidin (Li et al. 2006), minerals such as nitrogen, phosphorus, calcium, sodium, magnesium and potassium (Mirdehghan and Rahemi 2007) as well as complex polysaccharide (Jahfar et al. 2003). It has been reported that edible parts of fruit mainly consist of 10% seeds and 40% arils. Water is the main part in aril ~85%, total sugars 10% (consists of glucose and fructose), pectin 1.5%, other organic and bioactive compounds like citric acid, ascorbic acids, malic acid, as well as flavonoids and phenols majorly anthocyanins (Aviram et al. 2000; Tezcan et al. 2009).

Pomegranate has strong antioxidant activity due to different compounds of polyphenols mainly ETs, gallotannins, EA acid, and flavonoids such as anthocyanins, quercetin, kaempferol and luteolin glycosides (Tabaraki et al. 2012). Punicalagin, an ETs, is the most abundant polyphenolic compound in pomegranate peel and responsible for biological properties (Bopitiya and Madhujith 2012; Mena et al. 2013). In contrast to pomegranate peels, the seeds are mainly composed by fatty acids and in a lesser extent by antioxidants such as gallic acid, methyl ellagic acid, hydroxycinnamic acids and tocopherols (Lansky and Newman 2007).

The seeds comprise around 3% of total fruit weight with varying chemical compositions (Table 37.3). As far as oil content in seeds is concerned, it has been reported that quantity and quality of oil depends upon maturity and geographical location of cultivated pomegranate fruits.

Table 37.3 Physico-chemical properties of pomegranate seed oil
Full size table

The pomegranate seed oil consists of >90% polyunsaturated fatty acids (PUFA) such as linoleic, and linolenic acids (Tables 37.4a and 37.4b), as well as other fatty acids such as stearic, oleic, and palmitic acids (Fadavi et al. 2006; Özgül-Yücel 2005). Generally, seed oil of pomegranate contains high proportions of PUFA, especially conjugated fatty acids (Kaufman and Wiesman 2007). The seed also contains fibers, protein, minerals, vitamins, sugars, pectin, polyphenols, the sex steroid, estrone, isoflavones (mainly genistein) and the phytoestrogen coumestrol (El-Nemr et al. 1990; Syed et al. 2007). Tables 37.5a and 37.5b show the tocol and sterol contents of pomegranate seed oil. It is widely accepted that the beneficial health effects of fruits and vegetables in the prevention of disease are due to the bioactive compounds they contain (Galaverna et al. 2008). Almaiman and Ahmed (2002) reported phenols and ascorbic acid 1.90 and 0.18 mg/100 g, respectively in pomegranate seed. In Tunisian pomegranates, Amri et al. (2017a) has noted following compounds in seed oil like phenols 93.4 mg/kg, flavonoid 59.4 mg/kg, O-diphenols 30.1 mg/kg, and pigments (chlorophyll 3.17 mg/kg, and β-carotene 3.17 mg/kg).

Table 37.4a Individual fatty acid composition of pomegranate seed varieties available in the world
Full size table
Table 37.4b Fatty acid composition of phospholipids and glycolipids in pomegranate seed oil
Full size table
Table 37.5a Tocols content in extracted pomegranate seed oil
Full size table
Table 37.5b Content of phytosterols in pomegranate seed oils
Full size table

4 Pomegranate Seed Oil

Fatty acids are carboxylic acids with a long chain of aliphatic hydrocarbons either saturated or unsaturated. Fatty acids are found in open chain and derived from triglycerides or phospholipids. There are three types of hydrocarbons chain in fatty acids such as small, medium and long chain depends upon a number of carbon atoms present in the chain. The small chain consists of 4–6 carbon atoms, while the medium chain has 8–18 carbons and long chain contains above 18 carbons. Most of the plant seed oils usually contain unsaturated fatty acids in unconjugated form except a few seed oils, which contain conjugated double, triple or tetraenes bonds. Examples of conjugated double and triple bonds are conjugated linoleic acids (CLA) and conjugated linolenic acids (CLNA) . Presence of conjugated fatty acids in oil have been an object of studies. Basically, CLNA is a mixture of octadecatrienoic fatty acid isomers. These isomers include geometrical (cis and/or trans) and positional forms of linolenic acid (11,13,15–18:3, 10,12,14–18:3; 9,11,13–18:3; 8,10,12–18:3). A number of plant seeds contain very high concentration (30–70% of lipids) of CLNA isomers as shown in Table 37.6. Among them pomegranate seed oil contains a higher amount of CLNA. The important CLNA present in pomegranate seed oil is PA (Fig. 37.2) (9-trans, 11-cis, 13-trans) which consists of approximately 70–90% of total fatty acids (Abbasi et al. 2008; Tanaka et al. 2011).

Table 37.6 Conjugated linolenic acids contents in some oils (Tanaka et al. 2011)
Full size table
Fig. 37.2
figure 2

Molecular structure of punicic acid (PA)

Full size image

4.1 Punic Acid (PA)

It has been reported that PA showed a strong eicosanoid enzyme inhibition properties (Eikani et al. 2012). PA reduced fasting glucose in diabetics II, diet-induced obesity and insulin resistance, inflammation of colon, bladder, breast and prostate cancer, nephrotoxic activity, formation of hydroperoxide and improve bone mineral density (Banihani et al. 2013; Bouroshaki et al. 2010; Boussetta et al. 2009; Grossmann et al. 2010; Kohno et al. 2004; Lansky et al. 2005; Mukherjee and Bhattacharyya 2006; Spilmont et al. 2013; Wang and Martins-Green 2014). PA and α-EA also reduce the activity of sodium arsenite that is responsible for oxidative stress and deoxy (DNA) damage (Saha and Ghosh 2009).

4.2 FT-IR Spectrum of Pomegranate Seed Oil

The infrared spectrum of pomegranate seed oil is shown in Fig. 37.3. The characteristics functional groups present in pomegranate seed oil are resembled with other vegetable oils, except in the region of 1050–730 cm−1 due to the presence of CLNA. Prashantha et al. (2009) reported that isomers of eleostearic acid show a strong spectral band at 993 cm−1 corresponding to β-eleostearic acid (trans: trans: trans) and a doublet with a strong band at 991 cm−1 and a weaker band at 963 cm−1 corresponding to the α-eleostearic acid (cis: trans: trans). The corresponding doublet at 988 and 937 cm−1 in Fig. 37.3, confirmed the presence of CLNA in the pomegranate oil, in general these doublet bands are absent in vegetable oils.

Fig. 37.3
figure 3

FT-IR spectrum of pomegranate seed oil

Full size image