Amino acids are organic compounds that among other functions have an important role in protein biosynthesis and secondary metabolite syntheses. In addition to their role as building blocks of proteins, amino acids function as precursors or intermediates in bio-synthetic pathways such as production of color molecules and volatiles in fruits, energy release through degradation, signaling processes in plant metabolism regulation and plant stress response . Plants are a nutritional source for these elements and hence the importance of amino acid availability in fruits. There are very limited data and only a handful of research publications concerning amino acid in the pomegranate fruit.There are just two studies involving amino acid profile in pomegranate juice and they are incomparable . In this context, it should be pointed out that different detection methods might result in different amino acid compositions. Thus, one cannot conclude in general the composition of amino acids in pomegranate juices excluding the fact that serine is found at high percentages in all juices studied. Li et al. studied amino acids in juices of separated arils of six Chinese cultivars from two regions. Glutamine, serine, aspartate, and alanine are the most abundant amino acids in the juice, large plastic pots while glycine was not detected. All the essential amino acids exist but in smaller portions . Tezcan et al. analyzed fresh squeezed juice from three pomegranate fruits and three commercial pomegranate juices obtained from local markets .
The authors did not specify if the juice was squeezed from separated arils or from the intact arils. In addition to the L-amino acids that were identified, D-proline was detected in all the juices and D-leucine in one of the commercial juices. L-serine, L-proline, and L-alanine are themost abundant amino acids in these pomegranates juices, while D-leucine was not detected .El-Nemr et al. determined crude protein in fully ripened Egyptian pomegranate fruits obtained from the local market. The analysis discovered that seeds, but not juice, contain protein and that 13.2% of the constituents measured in the dry seeds were unidentified proteins . Al-Maiman and Ahmad studied total protein amounts in seeds of Saudi Arabian pomegranate “Taifi.” Fully-ripe fruits contained 4.06% of protein in the seeds . Elfalleh et al. studied proteins in the seeds of two Tunisian commercial pomegranate cultivars. Seed storage protein content was 167.8 ± 8.9 mg/g dry weight, which constitutes 16.9% of the seeds’ dry weight. Globulins and albumins are its major fractions, followed by glutelins and prolamins . No significant difference in the content of albumins and glutelins was found between the cultivars . Elfalleh et al. studied storage proteins in seeds of mature pomegranate fruits of eight different Tunisian cultivars from five Tunisian regions. The authors reported that the seeds contain 16.8% proteins . Glutelins constituted 16% and prolamins only 9% of the proteins found. Significant differences between the cultivars in the total amount of storage proteins, ranging from 15.4% in “Beldi” to 20.1% in “Rafrafi” was found, as well as differences for each fraction’s content . Zang determined protein content in pomegranate seeds oil originating from Xinjiang.
The average content of crude protein in pomegranate seeds was 14.3%, in which glutelins and residual protein constituted more than 80% of total protein content, and the contents of globulins, albumins, and prolamins were lower . In summary, it appears that there are differences in total protein content between pomegranate varieties. There is also variability in the content of the different storage proteins in the seeds. This variation may be connected to their genetic background but also to different analysis methods or environmental conditions.Al-Maiman and Ahmad studied total protein amounts in aril juice and seeds of Saudi Arabian pomegranate “Taifi” and compared unripe, half-ripe, and fully-ripe fruits. Protein concentration in seeds was found to be about four times higher than in the juice . No significant changes were observed in protein concentration during fruit development in the seeds. The juice of unripe fruits contained significantly less proteins than the quantities in half-ripe and fully-ripe fruits . Kulkarni and Aradhya reported total protein content in squeezed separated arils of the Indian “Ganesh” at seven fruit developmental stages . The study revealed significant changes in total protein content in the juice during fruit development. The highest total protein occurred 20 days after fruit set with a rapid decrease toward 80 days after fruit set. An increase occurred from 80 to 120 days and a significant slight decrease in total protein content occurred after 120 days . These two studies indicated that total protein content in the juice changes during pomegranate fruit development, but this does not happen in the seeds. Primary and secondary lipids have diverse functions in living organisms, including energy storage, cell signaling, nutrition , hormones, transport, and structural components of cell membranes.
The most lipidrich fraction in pomegranates is the seeds, which contribute 10% to fruit weight. Generally, seed oil constitutes 6–20% of seed weight and contains a large quantity of lipids . The chain length of the lipids is divided to three classes: Medium- , long- , and very long . The total lipid percentage in seeds varies from 4.4 to 27.2% . The list of lipids found in pomegranate fruit tissues is presented in Table 2. Punicic acid is the most abundant fatty acid in seed oil, constituting over 60% of the fatty acids, mostly followed by oleic acid, linoleic acid, and palmitic acid in a variable order . Triterpenoids and phytosterols have been found in pomegranate seed and fruit peel . The major phytosterol detected in seed oil is sitosterol . Most of the lipids were identified in the seeds, small amounts of lipids were also detected in aril juice and fruit peel. It should be mentioned that the presence of some of the lipids such as human steroid hormones is disputed .The oil consisted of 65–80% conjugated fatty acids of which punicic acid constituted 74–85%. Other major fatty acids were oleic, linoleic and palmitic acid. Polyunsaturated fatty acids constituted 87.2% of the total seed oil, while monounsaturated fatty acids constituted 7.1% and saturated fatty acids constituted 5.7% of the total amount of fatty acids in the seed oil. Total sterol content varied between 7.5 and 16.4 mg/g of oil. The major phytosterols detected were campesterol, stigmasterol, sitosterol, 1 5-avenasterol, and citrostadienol. Sitosterol constituted 65– 74% of the total sterols. Triterpene compounds cycloartenol and squalene constituted 0.8–2.4 mg/g oil and 0.7–3.2 mg/g , respectively. Phospholipids were 0.4–2.3% of the total lipids and phosphatidylethanolamine was the main compound, constituting 56–86% of total phospholipids. In addition, total tocopherol content ranged between 678.3 and 2627.4µg/g of oil, and γ-tocopherol, was 91% of the total tocopherols. There were significant differences between the varieties in fatty acids, sterols, phospholipids, and tocopherols. Differences were also found between variants of the same variety. Such are for example differences that were found between the landraces “Wonderful” and “Wonderful 1” in the content of oleic acid , and squelene . Jing et al. studied the lipid composition of extracted seed oil from four Chinese cultivars from Shanxi. Oil content in the seeds ranged from 114.2 to 147.9 mg/g and was significantly different between cultivars. 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. Seed oils by Pande and Akoh , Ferrara et al. , and Verardo et al. ; non-seed fruit tissues by Pande and Akoh . Seed oil was rich in polyunsaturated fatty acids , raspberry container which were significantly different in the four cultivars. Punicic acid was the dominant fatty acid . Total tocopherols ranged from 2,188 to 4,947µg/g. The four cultivars were significantly different in their lipid content . Another study in China examined the content and composition of fatty acid in the seed oil of pomegranates from Xinjiang. The oil content was 18.2%, and unsaturated fatty acids were more than 70% of total fatty acid . Ferrara et al. studied the oil content and fatty acid composition of 13 sweet and sour pomegranate genotypes from Puglia region in Southeastern Italy, of which 3 were of Israeli origin. The oil extracted from the dried seeds and the content of total lipids were significantly variable among these genotypes, ranging from 10.7 to 26.8% in sweet genotypes and from 4.9 to 17.4% in sour genotypes.
Sixteen fatty acids were identified in this study, among which punicic acid was the major fatty acid in all genotypes. Punicic acid content exceeded 74.9%, followed by palmitic, linoleic, stearic, and oleic acids. There was low variability of fatty acidcomposition between the genotypes. Unsaturated fatty acids in the seed oils constituted between 86.7 and 91.2% with saturated/unsaturated ratios ranging between 0.10 and 0.15 . Fadavi et al. determined the fatty acid composition of seed oil from 25 Iranian pomegranate varieties. Oil was extracted from dry seeds of commercially ripe fresh fruits from Markazi and Yazd provinces in Iran. Oil content ranged from 6.6 to 19.3% . The pre-dominant fatty acid was linolenic acid–31.8–86.6%—followed by linoleic acid, oleic acid, stearic acid, and palmitic acid . Worth noticing is the fact that punicic acid was not detected in this study. This fatty acid was found to be the predominant acid in pomegranates in many other studies but was not detected in these varieties. Since punicic and linolenic acids are isomers, this might be a result of different classification or misinterpretation of the molecule’s nature. Differences between the varieties were significant. Moreover, differences were found in the lipid contents of sweet, sour, and sour sweet varieties while the lowest was in sweet varieties and the highest in sour sweet. The profile of fatty acids and phytosterols in pomegranate seed oil from four varieties grown in Israel was determined. Results showed linolenic acid to be the predominant fatty acid . The linolenic acid fraction was composed of four different chromatographically separate peaks that are assumed to be attributed to different isomers of conjugated linolenic acid, and punicic acid was the major isomer. Phytosterols were found at quite a high concentration with a wide variety of components, and the major phytosterols were β-sitosterol, campesterol, and stigmasterol . Fatty acid and tocopherol composition in the seed oil of nine worldwide pomegranate varieties that were grown in Spain was analyzed resulting in 4.4–12.0% oil content. Over 86% of the oil were unsaturated fatty acids, mainly punicic acid, ranging between 77.3 and 83.6% of total fatty acids. Total tocopherols ranged from 174.5 to 627.3 mg/100 g oil, mainly γ-tocopherol. There were significant differences between the cultivars . Lipids were also studied in local varieties from some other countries. Fatty acid content was studied in seeds of fully ripened local market Egyptian pomegranate fruits. Total lipids were 27.2% with saturated fatty acids being 83.6% of the total fatty acids. The predominant acid was caprylic acid , followed by stearic acid, oleic and linoleic acids out of 11 fatty acids that were identified . Punicic acid or linolenic acid were not detected. The oil content and fatty acid composition of the seed oil of seven Spanish sweet pomegranate varieties was 6.3–12.2%, of which 73.4–95.8% were unsaturated fatty acids. The predominant fatty acid was linolenic acid , followed by linoleic acid, oleic acid, and palmitoleic acid. Differences in fatty acid composition were found among the varieties studied . Fatty acid composition in the seed oil of 25 pomegranates varieties from two different regions of India showed oil content of 6.6–19.3%, most of it unsaturated fatty acids. The predominant fatty acid was linolenic acid , followed by linoleic acid, oleic acid, stearic acid and palmitoleic acid. The varieties studied had similar but not identical fatty acid composition Parashar et al., 2010). Significant differences were found in studies conducted with different varieties in different regions of the world, indicating that genetic background influences this trait. Nevertheless, the general structure of lipids, mainly in seed oil, is very similar . The vast majority of the fatty acids are unsaturated fatty acids and punicic acid is by far the main fatty acid. Sitosterol is the most abundant phytosterol in pomegranate seed oil.Pande and Akoh investigated the lipid profiles of six Georgia pomegranate varieties. Ripe fruits were used for the preparation of two fractions: seed tissue and non-seed tissues .