Analysis of the Phytochemical Composition of Pomegranate Fruit Juices, Peels and Kernels: A Comparative Study on Four Cultivars Grown in Southern Italy

Abstract

The increasing popularity of pomegranate (Punica granatum L.), driven by the awareness of its nutraceutical properties and excellent environmental adaptability, is promoting a global expansion of its production area. This investigation reports the variability in the weight, moisture, pH, total soluble solids, carbohydrates, organic acids, phenolic compounds, fatty acids, antioxidant activities, and element composition of different fruit parts (juices, peels, and kernels) from four (Ako, Emek, Kamel, and Wonderful One) of the most widely cultivated Israeli pomegranate varieties in Salento (South Italy). To the best of our knowledge, this is the first systematic characterization of different fruit parts from pomegranate cultivars grown simultaneously in the same orchard and subjected to identical agronomic and environmental conditions. Significant genotype-dependent variability was observed for many of the investigated parameters, though without any correlation among fruit parts. The levels of phenols, flavonoids, anthocyanins, and ascorbic and dehydroascorbic acids of all samples were higher than the literature-reported data, as was the antioxidant activity. This is likely due to positive interactions among genotypes, the environment, and good agricultural practices. This study also confirms that pomegranate kernels and peels are, respectively, rich sources of punicic acid and phenols together, with several other bioactive molecules. However, the variability in their levels emphasizes the need for further research to better exploit their agro-industrial potential and thereby increase juice-production chain sustainability. This study will help to assist breeders and growers to respond to consumer and industrial preferences and encourage the development of biorefinery strategies for the utilization of pomegranate by-products as nutraceuticals or value-added ingredients for custom-tailored supplemented foods.

Keywords: Punica granatum L.; agri-food by-products; antioxidants; ascorbic acid; flavonoids; fruit peels; juices; phenolic compounds; seeds; sugars.

Figure 1

Anatomy of a typical pomegranate fruit and seed (aril).

Figure 2

(a) External appearance, longitudinal sections, and average weight (±standard deviation) of ripe fruits of different pomegranate cultivars grown in an open field in the south of Italy. Fruit weight data were submitted to one-way analysis of variance (ANOVA) and differences among cultivars were detected using multiple comparison procedures (Holm–Sidak post hoc test, n = 20, p < 0.05) and indicated with different superscript letters. (b) Macroscopic appearance of the juice, kernel, and peel fruit parts isolated from a representative fruit (cultivar: Wonderful One) and the relative average percent weights for each cultivar under analysis.

Figure 3

Profiles of the main soluble sugars (a) and organic acids (b) detected in the juices and peels isolated from the ripe fruits of different pomegranate cultivars grown in an open field in the south of Italy. Values represent the mean ± standard deviation of three independent sampling replicates (n = 3). Data were submitted to one-way analysis of variance (ANOVA) and differences among cultivars, within each category, were detected using multiple comparison procedures (Holm–Sidak post hoc test, p < 0.05) and indicated with different letters.

Figure 4

Profile of the main anthocyanins detected in the juices and peels isolated from the ripe fruits of different pomegranate cultivars grown in an open field in the south of Italy. Values represent the mean ± standard deviation of three independent sampling replicates (n = 3). Data were submitted to one-way analysis of variance (ANOVA) and differences among cultivars, within each category, were detected using multiple comparison procedures (Holm–Sidak post hoc test, p < 0.05) and indicated with different letters.

Figure 5

Principal component analysis (PCA) biplot of PC1 vs. PC2 of fruit quality attributes (moisture, total ethanol-soluble carbohydrates (TESC)), total ethanol-insoluble carbohydrates (TEIC)), functional quality attributes (total soluble phenolic compounds (TSPC), total insoluble-bound phenolic compounds (TIBPC), total flavonoid compounds (TFC), total anthocyanins (TA), ascorbic acid (AsA), dehydroascorbic acid [DAsA), antioxidant activities (hydrophilic antioxidant activity (HAA), lipophilic antioxidant activity (LAA), total antioxidant activity (TAA)), and element composition of different fruit parts (juice, kernels and peels) isolated from the ripe fruits of different pomegranate cultivars grown in an open field in the south of Italy. The variance (%) explained by each PCA axis is given in brackets. The length of the vectors is correlated to their significance within each population. Between vectors and between a vector and an axis, there is a positive correlation if the angle is <90°, whereas the correlation is negative if the angle reaches 180°. There is no linear dependence if the angle is 90°. A, Ako; E, Emek; K, Kamel; W, Wonderful One.