Fermentation of Date Pulp Residues Using Saccharomyces cerevisiae and Pichia kudriavzevii—Insights into Biological Activities, Phenolic and Volatile Compounds, Untargeted Metabolomics, and Carbohydrate Analysis Post In Vitro Digestion

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.