Comparison of some Physicochemical Characteristics and Polyphenolic Content in Six Pomegranate (Punica granatum) Cultivars

IntroductionPomegranate (Punica granatum L.) is a nutrient dense fruit with a high health value and one of the most important Iranian fruit crop. Historical evidence reveals that the primary origin of pomegranate is Iran and that it has been spread from this region to other areas. A vast range of pomegranate varieties can be found in Iran; 760 original, decorative and wild ones. Pomegranate juice contains a high amount of total soluble solid (TSS), anthocyanins, polyphenolic compounds, vitamin C, sugars and proteins.Pomegranate is considered as one of the most tolerant fruit crops capable of growing under arid and semi-arid climatic conditions. Cultivar and growing region climate are the main factors determining chemical composition of pomegranate fruits; Significant differences in various fruit quality parameters such as organic acids, phenolic compounds, sugars and water-soluble vitamins have been reported in previous studies.  The aim of present study was to compare and evaluate physical and biochemical characteristics of fruits and different polyphenolic compounds in juice of six commercial Iranian pomegranate cultivars.Materials and MethodsThis research was conducted in 2017 and 2018 years in a commercial orchard in Arsanjan region of Fras province. Six Iranian pomegranate cultivars included ‘Malas Yusef Khani’ (MYK), ‘Bajestani (BK), ‘Khazr Bardskan’ (KHZ), ‘Malas Dane Syah’ (MDS), ‘Rabbab’ (RB) and ‘Zard Anar Arsenjan’ (ZA) were studied. The trees were planted in randomized block design and spaced 5 and 3 m between and along the rows, respectively. The trees were grown under drip irrigation with routine cultural practices suitable for commercial fruit production. Orchard management was conducted uniformly according to optimized available recommendations (based on soil and water samples analysis) for the orchard site. Fruits were harvested randomly from orchard and some physicochemical characteristic of fruits were measured. Fruit length and fruit diameter measured by manual caliper, fruit and above ground weight was determined by digital scale. The fruit juice percentage was calculated by calculating the percentage of aril juice.  TSS (Total soluble solids) expressed in Brix◦ was measured using a refractometer. The titrable acidity (TA) was determined by titration to pH 8.1 with 0.1M NaOH solution and expressed as percentage.Total anthocyanins, total polyphenols, vitamin C and anthyoxidant activity were measured spectrophotometrically. Polyphenolic compositions of juices (Gallic acid, Catechin, Caffeic acid, Chloregenic acid, p-Coumaric acid Vanilin, Trans-ferulic acid, Hesperedin and Ellagic acid) were also measured using HPLC analysis. The chromatographic analysis was carried out on Agilent Technologies 1200 series HPLC system. Chromatograms were recorded at 280 and 320 nm. Each compound was quantified by comparing its peak. Data was analyzed by SPSS software and means were compared using Duncan’s multiple range tests at 5% probability level. Results and Discussion Significant differences were found among studied pomegranate cultivars for various physical fruit characteristics, quality parameters and polyphenolic composition of fruit. ‘Malas Daneh Syah Yazd ’was the best in comparison to other cultivars.  ‘Malas Daneh Syah Yazd’ had the highest fruit weight (332 g), fruit length (8 cm), fruit diameter (8 cm), TSS(15.77 Brix◦), anthocyanin content (26.98 mg 100 ml-1), polyphenol content (514.37 mg 100 ml-1) , ascorbic acid content (9.23 mg 100 ml-1) and antioxidant activity (52.2%). Also, the amount of polyphenols in this cultivar was relatively high. This cultivar had high amount of some polyphenol content such as cathechin (223.5 mg L-1), Hesperidin (30.55 mg L-1) and Ellagic acid (43.02 mg L-1) with no significant differences with highest amount. ‘Rabbab’ had the highest aril weight (340 mg) and moderate levels of other fruit characterestics, this cultivar had the maximum polyphenols such as gallic acid (163.1 mgL-1), catechin (264.2 mgL-1), caffeic acid (265.1 mgL-1), p-Coumaric (74.41 mgL-1) acid, vanillin (18.21 mgL-1) and ellagic acid (43.5 mgL-1). Zard anar’ pomegranate cultivar which was native to this region in terms of most biochemical properties had a low a‘mount .Therefor, among the studied pomegranate cultivars‘ Malas Dane syah’ and was the best. This cultivar had the highest fruit characteristics and polyphenol content such as ellagic acid. ConclusionThe results of this study showed significant differences among studied pomegranate cultivars. ‘Dane syah Yazd’ had the highest physical and chemical characterestics of fruits. Previous studies showed that theses cultivars had good growth characteristics and high yield in comparison to other cultivars. Therefore, among the studied cultivars, ‘Dane syah Yazd’ is introduced as a suitable cultivar for this region. Also, ‘Rabbab’ Neyriz cultivar can be considered as a cultivar with high antioxidant properties of fruit juice due to having the highest amount of measured polyphenolic compounds, especially alginic acid.