Introductory Chapter: Pomegranate

1. Introduction

1.1 Antioxidant properties and bioactive polyphenolic ingredients in pomegranate varieties

Pomegranate (Punica granatum L.) has been used extensively in folk medicine of many cultures. The popularity of pomegranate has increased tremendously especially in the last decade due to its antimicrobial, anti-viral, anti-cancer, powerful antioxidant and anti-mutagenic effects of the fruit [1, 2, 3, 4]. Pomegranate juice has been proposed as a chemopreventive, chemotherapeutic, antiathero-sclerotic and anti-inflammatory agent. Polyphenols, which represent the predominant class of phytochemicals in pomegranate, consist mainly of hydrolyzable tannins such as gallotanins, ellagitannins and ellagic acid, components which have high antioxidant activities [5, 6, 7, 8].

These activities are attributed to the pomegranate’s high levels of polyphenols content. Polyphenols, represent the predominant class of phytochemicals of pomegranate fruits, mainly consisting of hydrolysable tannins which are mainly located in the fruit peel and mesocarp of pomegranates. Chemical analyses have shown that the pomegranate (juice) contains a significantly high level of hydrolysable tannins, such as gallotannins, ellagitannins and ellagic acid, which exhibited high antioxidant activities [9].

Ellagic acid has been found to exhibit antimutagenic, antiviral, whitening of the skin and antioxidant properties. EA exhibits significant anti-mutagenic, antitoxic, anti-apoptotic, anti-cancer, antibacterial, antiviral, anti-diabetic and anti-inflammatory properties [10, 11, 12].

Urolithins are products of metabolism of ellagic acid through the loss of one of the two lactones (lactonase/decarboxylase action) and by successive hydroxyl removal (dehydroxylase activities). In vitro trials have shown anti-inflammatory, anti-cancer, anti-glycemic, antioxidant and antimicrobial effects of urolithins, supporting their potential health benefits attributed to foods rich in pomegranate and ellagitannins [13].

The antioxidant properties and the presence of antioxidant compounds has been reported mostly for pomegranate juice [14, 15, 16] however, increasing literature was found reporting the antioxidant activity of pomegranate peels and seeds [16, 17, 18].

The extensive knowledge about pomegranate’s health attributes and public awareness about nutritional food has increased the demand for the industrial use of pomegranate fruit and its byproducts (peels and seeds). The peels and seeds, which are usually disposed of as waste material in many food-processing industries, could be a rich source of beneficial phytochemicals [19].

Methanol and/or combinations of methanol and other organic solvents have been used for the extraction of polyphenols from pomegranate peels [17, 18]. It is also important to study the use of water as an alternative solvent for the extraction of polyphenols because it is easily accessible, non-toxic, environmentally friendly, and non-hazardous to operator health.

2. Previous studies: Results

A study presented by Lagouri et al., in the 6th International Conference on “Oxidative Stress-Skin Biology and Medicine” 2014 with the title: “Antioxidant properties and phenolic content of Greek pomegranate cultivars” was performed in order to quantify total phenols, flavonoids, hydrolyzable tannins and ellagic acid in the juice, and in the peel and seed extracts of two pomegranate varieties from mainland Greece (Central Macedonia and Thrace) with high pressure liquid chromatography method.

The aims of the study were to prepare aril juices, peel homogenates, peel and seed aqueous and methanolic extracts of two pomegranate cultivars collected from mainland Greece (Central Macedonia: B cultivar and Thrace: C cultivar) and to evaluate:

• their antioxidant properties by using free radical scavenging (DPPH) and ferric reducing antioxidant power (FRAP) assays

• their total phenols (TP), total flavonoids (TF), hydrolysable tannins (HT) and ellagic acid (EA) contents by using spectrophotometric and high pressure liquid chromatographic methods [20, 21, 22, 23, 24].

In total as shown in Figures 1–3, the peels from both pomegranate cultivars had higher antioxidant activity and phenol contents compared to juices and seeds. In addition, the B cultivar (Central Macedonia) in its peel homogenates showed higher free radical scavenging activity, total phenol, total flavonoid, hydrolysable tannins and ellagic acid contents than the C cultivar (Thrace). From the results it can be concluded also that different solvents (methanol, water) at temperatures 24 and 40°C used during the extraction process of the peels may affect their antioxidant properties and phenol contents.

Figure 1.

DPPH assay.

Figure 2.

FRAP assay.

Figure 3.

Total phenols assay.

In conclusion the results of the study were very promising because pomegranate peels and seeds, which are commonly disposed of as waste in many food processing industries, could be important sources of phytochemicals.