Date palm fruits (Phoenix dactylifera L.) were found to contain high levels of allomelanin (1.2–5.1%). The melanin is localized in the tanniferous cells between the inner and outer mesocarp tissues of the fruit. The melanin, extracted with 2 M sodium hydroxide, consisted of amorphous graphene-like granular structures of irregular shape and variable size. The date fruit melanin mainly comprises carbon (64.6%) and oxygen (30.6) but no nitrogen, and was thermally stable. It has radical scavenging (63.6–75.1 IC₅₀, µg/mL), antimicrobial (250–1000 µg/mL), hypoglycemic (51.8–58.2%), and angiotensin-converting-enzyme inhibitory (65.8%) effects. The high level of melanin in date fruits highlights the importance of investigating its dietary intake and its impact on nutrition. This study also suggests that date fruit melanin can be a functional ingredient in foods, food packages, pharmaceuticals, and cosmetics.

Utilizing agricultural byproducts, such as date pulp residue (DPR), can contribute significantly towards achieving sustainable food production. This paper aimed to investigate the physicochemical properties of DPR and evaluate the health benefits of nonfermented and fermented DPR samples both pre- and post-digestion (bioaccessible portions). Additionally, it aimed to analyze the carbohydrates and untargeted metabolites in the bioaccessible portions. Fermentation of DPR by Saccharomyces cerevisiae and Pichia kudriavzevii resulted in an abundance of malic acid (over 2400 mg/100 g) and the identification of 42 volatiles, with different degrees of predominance observed in the samples. Twenty phenolics were determined by UPLC in fermented DPR, with (-)-epicatechin, tyrosol, and gallic acid being the most abundant. Bioaccessibility studies revealed that fermented DPR samples retained at least ~44% of α-glucosidase inhibition and exhibited improved α-amylase inhibition compared to nonfermented and undigested samples. In vitro cytotoxicity assays showed a more potent inhibitory effect of fermented DPR against MCF-7 and Caco2 cell lines (average inhibition of 55% and 74.4% for the two types of fermented samples) compared to nonfermented DPR. The untargeted metabolomics analysis identified C5-branched dibasic acid metabolism as the most prominent pathway, with four metabolites identified. Furthermore, the analysis of bioaccessible carbohydrate metabolites in the fermented DPR using LC-QTOF showed the presence of a group of phytochemicals, including three terpenoid metabolites.