Date Industry by-Product: Date Seeds (Phoenix dactylifera L.) as Potential Natural Sources of Bioactive and Antioxidant Compounds

The chemical composition, carotenoids, anthocyanins, total phenolic content, total flavonoid content, and antioxidant activity of three date seed cultivars, mainly Barhi, Ruthana, and Qatarah, were investigated. Date seed bioactive compounds were extracted by using different extraction solvents. The chemical analysis revealed that the Barhi cultivar has the highest moisture and fat content, while Ruthana has the highest carbohydrate content. There were no significant differences in protein and ash contents among the three date seeds. Ethanol (100%) showed the highest bioactive compound contents and antioxidant activity, whereas water showed the lowest content among the six solvents. Generally, all the date seed cultivars contain high amounts of phenolic, flavonoid, and antioxidant activity. The carotenoid content was highest in the Barhi (1.98 mg/g DW) followed by Qatarah (1.25 mg/g DW) and Ruthana (0.89 mg/g DW) seed, while the anthocyanin content was highest in the Ruthana cultivar (5.51 ± 0.71 cyanidin 3-glucoside/g DM.) and lowest in Barhi date seed (3.335 ± 0.23 cyanidin 3-glucoside/g DM.). Among the three date seeds, the Ruthana seed showed the highest phenolic (93.36 ± 0.30 mg GAE/g) and flavonoid compounds (59.9 ± 0.44 mg CE/g), DPPH activity (78.6 ± 0.92%), and total reducing power (60.3 ± 0.09%). The optimum solvent for the extraction of the antioxidants and their activity in each date seed was validated by using partial least squares regression (PLS). The results revealed a variation in the valid and optimum extracts for each seed; 100% ethanol extract for Barhi seed and mixture of methanol:ethanol:water (M 40:E40:W20) extract for Ruthana and Qatarah cultivars were the best solvent systems. The high natural antioxidant content of date seeds indicates that they can be considered functional ingredients for food and medicinal uses.