Study of some physicochemical properties and antioxidant activity of some date (Phoenix dactylifera L.) cultivars from different locations in Alwahat region - Libya

Abstract

Abstract This study was conducted on three cultivars of dates from four different sites (two sites for each cultivar), namely Deglet, Saidy, and Teads, which grow in the Alwahat province - Libya, samples were collected in mid-September 2017, the research included a study of the physical properties of fruits including the color characteristics, number of fruits per kilogram, the weight of 100 fruits, the weight of 100 seeds, an average of fruit and seed, pulp weight, the length and diameter of fruit and seed and the percentage of seed weight from fruit, total soluble solids, total acidity, and pH value. The chemical properties included studying approximate fruit analysis, estimating the sugar content, minerals, in addition to estimating total phenols, total flavonoids, and antioxidant activity using DPPH, ABTS, and reducing power assay. Physical properties results showed that Teads laba cultivar had the highest number of date per kilogram (151 fruit), while Saidy mashrooh cultivar had the lowest (90.67 fruit). On the other hand, Teads laba cultivar was the lowest for the weight of 100 fruits (653g) with an average of 6.35g whereas, Saidy mashrooh cultivar was the highest (1147.67 g) with an average of 11.48g. The weight of 100 seeds ranged from 85 to 151.67 g within average from 0.85 to 1.52 g. Pulp weight and the percentage of seed weight from the fruit were between (4.97- 9.98g) and (9.84- 21.73 %), respectively. Fruit length, fruit diameter, seed length, and seed diameter ranged from 1.87 to 3.68, 1.41 to 1.91, 1.87 to 2.24, and 0.46 to 0.72, respectively. Deglet mashrooh had the highest value of total acidity (0.284% based on dry weight (dw)) while Saidy mashrooh had the lowest value (0.240% dw), and the differences among cultivars not always significant (P > 0.05). Saidy mashrooh exhibited the highest pH value (6.86) while Deglet nahr exhibited the lowest value (5.87), and the difference in pH values among cultivars was significant (P ≤ 0.05). Total soluble solids for Deglet nahr, Deglet mashrooh, Saidy nahr, Saidy mashrooh, Teads laba, and Teads shurof were 82.88, 82.70, 86.68, 84.87, 82.32, and 81.62 degrees Brix, iv respectively. The results of estimating color properties using Hunter Lab showed a variation in values between fresh and freeze-dried date fruits. Regarding chemical properties, the results showed that the moisture content of date fruits ranged from 10.36% (Saidy nahr) to 26.92% (Deglet mashrooh), ash content varied from 1.85% to 2.23% where Teads laba showed the highest content while Deglet nahr showed the lowest in this respect. The differences in moisture and ash content among cultivars were not always significant (P > 0.05). The crude fat contents ranged from 0.043-0.23% dw and the difference among cultivars not always significant (P > 0.05). The crude protein content ranged from 2.93-3.43% dw where Teads shurof cultivar had significantly (P ≤ 0.05) lower protein content among cultivars. Crude fiber and nitrogen-free extract values ranged from 2.10-2.89% and 91.64-92.82% dw respectively and the differences were not always significant (P > 0.05). The total carbohydrate content ranged from 94.25-94.96%, the differences among cultivars were not always significant (P > 0.05). The reducing sugars content ranged from 31.19% for Deglet nahr to 75.23% for Saidy mashrooh, while the non-reducing sugars and total sugars content ranged from not detectable to 40.30% and 71.49 to 75.23% dw respectively. It is worth paying attention to the non-reducing sugars result obtained for the Deglet cultivar was higher compared to reducing sugars. The differences in reducing sugars, nonreducing sugars, and total sugars content among cultivars were not always significant (P > 0.05). The results of individual sugars analysis using HPLC system showed that fructose is the predominant sugar in date fruits except for Deglet cultivar, where the value ranged from 22.08-51.15% dw, followed by glucose sugar values ranging from 17.45-38.74% dw. However, the sucrose content was the highest in Deglet nahr and Deglet mashrooh with values of 40.98% and 35.92% dw respectively, maltose content was undetectable in all cultivars. The differences in the individual sugars content among cultivars were not always significant (P > 0.05). v The findings of the mineral elements analysis showed that potassium is the dominant element in all date cultivars with values ranging from 8394.57 to 11736.85 ppm dw, then calcium with values ranging from 662.27 to 844.95 ppm dw, followed by magnesium, phosphorus whereas sodium was mostly the lowest element among the major elements analyzed, the values of iron, zinc, and copper ranged from 7.39 to 10.55, 3.58 to 5.83 and 2.53 to 3.63 ppm respectively, the highest concentration of which was iron followed by zinc and the lowest concentrated element was copper. On the other hand, mineral pollutants As, Pb, Cd, and Hg showed no tangible values or above safety baseline levels according to Libyan standards limits except Saidy mashrooh cultivar in Cd element level. The content of total phenolic ranged from 16.80 for Teads shurof to 24.78 Gallic acid equivalent per 100 g on a dry weight basis (GAE/100 g dw) for Saidy nahr, whereas the total flavonoids content ranged from 3.82 to 8.35 catechin equivalent per 100 g on a dry weight basis (CE/100g dw). The statistical analysis showed that the differences in total phenolic and flavonoids content among cultivars were not always significant (P > 0.05). The antioxidant activity of different date cultivars using DPPH free radical scavenging assay expressed as IC50 ranged from 31.38 to 60.54 mg/ml. while the ABTS values were 16.85 to 27.37 mg/ml and the reducing power values ranged from 16.11 to 25.63 mg/ml. The differences in the antioxidant activities among cultivars were not always significant (P > 0.05). A high positive significant correlation was found between total phenolic and antioxidant activities also, the correlation between DPPH and ABTS assay (r = 0.994, P < 0.001) was highly significant. while a weak positive significant correlation was found between total phenolic and total flavonoids