The physicochemical characterisation and morphometric analysis of pomegranates (Punica granatum L.) cultivated in the Maltese Islands

Abstract

Punica granatum L. is beloved globally for its comprehensive range of nutritional and nutraceutical constituents. This empirical study aimed to establish the basis of pomegranate cultivation and obtain a holistic representation of the full potential of the ‘fruit of paradise’ as pertaining to the central Mediterranean. Several intrinsic visual, physical, and chemical characteristics were investigated along with the various flowering and fruit maturation stages of 35 different accessions cultivated in 5 distinct regions in the 2021 growing season. The morphological properties of the leaf, flowering buds, blooms, and fruits at 3 ripening stages expressed significant differences as well as similarities between the accessions in most of the parameters investigated. Matured fruits FW ranged between 87 ± 8.06 – 586 ± 88.6 g, longitudinal diameter between 4.86 ± 0.27 – 9.13 ± 0.23 cm, equatorial diameter between 5.29 ± 0.30 – 10.7± 0.37 cm, sphericity between 0.77 ± 0.01– 0.98 ± 0.03, and rind thickness between 2.14 ± 0.03 – 4.33 ± 0.03 mm. 3 types of fruit crowns were expressed, being either closed, opened or semi-opened, while fruits possessed either 6 or 8 sepals, according to the cultivar. It was also concluded that the growing regions and age of pomegranate shrubs appeared not to affect these parameters. Rather, slight variations in development stages, climatic, environmental and cultivation conditions, as well as genetic variability and diversity were responsible. Furthermore, PCA and AHC analysis of the ripened pomegranates generally revealed the distinction between the ‘Santa Rosa’, ‘Unknown’, ‘Acco’, ‘Santa Katarina’, and ‘Ħelu’ cultivars, while almost all the ‘Bullar’, and ‘San Ġużepp’ accessions expressed significant morphological similarities. The pH and TSS increased while TA decreased along fruit maturation, resulting in the majority of local accessions having a moderate (sour sweet to sweet taste) and relative high MI (sweet taste). Colour variation was associated with increased TAC and decreased lycopene, total carotenoids, and total chlorophyll content along the fruit ripening stages. The lowest TPC was recorded in ripened pomegranates ranging between 0.111 – 0.635 % w/w GAE. Overall, the pulp of ripened pomegranates recorded the quantitative descending order of K > Ca > Na > Mg > Fe, and apart from the latter micronutrient, the other macronutrients exhibited a decreased accumulation along fruit ripening. The peel and pulp physicochemical parameters revealed several strong positive and negative correlations, concluding amongst which that MI can serve as an effective estimate for both the TA and pH when comparing local pomegranates. In conclusion, this study revealed that local pomegranate peel exhibits a substantial nutritional potential due to significantly higher TAC (∼ 3.5-fold), TPC (∼ 5.7-fold), lycopene (∼ 5.6-fold), % total carotenoids (> 10-fold), % total chlorophyll (∼ 4.6-fold), Ca (∼ 5.2-fold), Mg (∼ 3.5-fold), K (∼ 3-fold), Na (∼ 1.5-fold), and Fe accumulations than the fresh juice of ripened fruits, meaning that instead of being discarded, this inedible pomegranate part can be sustainably exploited in the food, cosmeceutical, and pharmacological industries. Thus, Maltese-grown pomegranates hold the potential for versatile and holistic utilisation that should be further exploited, not only agriculturally but also as effective alternatives in several important industries.