Effect of different drying methods and storage conditions on physical, nutritional, bioactive compounds and antioxidant properties of doum (Hyphaene thebaica) fruits

The present study reports effect of various drying and storage conditions on physical, bioactive compounds, and antioxidant properties of doum (H. thebaica) fruit for the first time. Three types of fruit are used such as fresh, dried from tree, and dried fruits purchased from local market. Pulp of fresh fruit was dried using sun, shade and oven at different temperatures and stored under different conditions for three months. Samples were analysed before and after drying and storage. The results showed significantly (p < 0.01) higher dry matter (98.73 g/100g), pH (7.09), tannins (27.64 mg/g), flavonoids (19.90 mg/g) and total polyphenols (7.13 mg/g) contents in pericarp than other parts of fruit. The pulp without pericarp exhibited higher ash, amino acids, proteins and vitamin C contents, however pulp of whole fresh fruit had higher Ca (1.67 mg/g), Na (640.26 mg/g) and Zn (11.63 μg/g). Pulp of fruit purchased from local market showed significantly stronger antioxidant activities (DPPH and ABTS). All parameters evaluated were significantly (p < 0.01) affected in comparison with pulp of fresh fruit but varied with respect to drying methods and storage conditions. The shade-dried samples showed higher proteins, amino acids, vitamin C, ash, fibres and acidity contents than other drying methods. Polyphenols and antioxidant activities are higher in oven-dried samples at low temperature (40 °C) as compared to others. The highest DPPH and ABTS scavenging activities are observed after drying and storage conditions for three months. Significant and positive (p < 0.01) correlations are found between antioxidant compounds and antioxidant activities. Thus, drying methods and storage conditions can preserve pulp of doum fruit with high physicochemical, bioactive compounds and antioxidant capacities for human well-being up to three months, however shade-drying followed by oven-drying are highly promising process that must be considered as suitable drying methods for doum fruits.