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.

Polyphenols in cassava leaves (Manihot esculenta Crantz) and their stability in antioxidant potential after in vitro gastrointestinal digestion

The study was carried out to assess the effect of variety on polyphenols in cassava leaves and their stability in antioxidant activity before and after in vitro gastrointestinal digestion. The results showed that individual and total polyphenols content (TPC) and antioxidant activity of bound, free and bioaccessible polyphenols were significantly (p < 0.05) influenced by variety at harvesting maturity. The bound polyphenols had lower TPC (5.00-19.16 mg GAE/g) than free (39.16-89.61 mg GAE/g) throughout harvesting maturity. The polyphenols were strongly affected after in vitro digestion, however, salicylic, syringic and benzoic acids are the most bioaccessible. The free polyphenols of variety IRAD4115 had the highest value of FRAP (35.17 μg TE/g) at 12 months after planting (MAP), while, bound polyphenols showed the lowest DPPH (6.59 μg TE/g, variety EN at 12MAP). The antioxidant activity value evaluated by DPPH method was decreased significantly after in vitro gastrointestinal digestion. However, there was no significant difference between antioxidant activity of bioaccessible polyphenols (77.71 μg TE/g) and methanolic polyphenols (79.17 μg TE/g) assessed by FRAP method. These findings showed the stability of antioxidant potential of polyphenols in cassava leaves harvested at different periods after in vitro digestion. Thus cassava leaves harvested at appropriate maturity can be used as ingredient of functional food for nutraceutical benefits.