Primary Metabolites, Anthocyanins, and Hydrolyzable Tannins in the Pomegranate Fruit

Abstract

Pomegranate (Punica granatum L.) is an important and interesting fruit tree that is cultivated in many parts of the world. In recent years, along with the increase in its cultivation and consumption there has been a dramatic increase in the scientific interest in its biology, methods of cultivation, adaptation to environmental cues and its health-promoting properties. Quite a large proportion of the various metabolites produced in the pomegranate were determined and their content in the bark, roots, leaves, and fruit was reported. Many reviews on polyphenolic compound content, antioxidant activity and health-promoting compounds were published recently. However, only very few recent reports were dedicated to primary metabolites, despite the fact that much work was done on organic acids, sugars, proteins, lipids, and amino acids of the pomegranate fruit. In this review, a special effort was made to present these recent studies and the review is devoted to primary metabolites. The reported data show high variation in the content of primary metabolites within the pomegranate fruit; therefore the data is presented (whenever possible) according to fruit tissues (peel, arils, and seeds), developmental stages of the fruit, environmental and climatic conditions, and genetic background. Most of the data on pomegranate is based on metabolic content and contains no genetic or molecular analysis except for work done on anthocyanins and hydrolyzable tannins. In those cases, gene assignment and genetic control studies were pointed out in the review. The recent publication of the genome sequences from several pomegranate varieties and transcriptomic data from fruits, flowers, and leaves is expected to facilitate the understanding of genetic control of metabolites in pomegranate.

Keywords: fruit; lipids; metabolites; organic acids; polyphenols; pomegranate; proteins; sugars.

Figure 1

Schematic illustration of the main sugars content in pomegranate juice from different varieties grown in Tunis, Turkey, Spain, and Israel. The values presented are average values of the percentage of each sugar of the total amount of sugars measured by Melgarejo et al. (2000); Tzulker et al. (2007); Hasnaoui et al. (2011); Caliskan and Bayazit (2012).

Figure 2

Schematic illustration of amino acid content in pomegranate fruit tissues from different varieties and countries. The values presented are average values of the percentage of each amino acid of the total amount of amino acids measured: (A) juice from China by Li et al. (2017); (B) juice from Turkey by Tezcan et al. (2013); (C) peel powder from Egypt by Rowayshed et al. (2013); (D) seed powder from Tunisia and Egypt by Elfalleh et al. (2011) and Rowayshed et al. (2013).

Figure 3

Schematic illustration of fatty acid content in pomegranate fruit tissues from varieties of different origin. The values presented are average values of the percentage of each fatty acid of the total fatty acids measured. (A) Seed oils by Pande and Akoh (2009), Ferrara et al. (2014), and Verardo et al. (2014); (B) non-seed fruit tissues by Pande and Akoh (2009).

Figure 4

Fruit peel and arils of various varieties in the Israeli pomegranate collection display a wide range of colors.