Enhanced Biological Potential and Phytochemical Profiling of <i>Phoenix Dactylifera</i> Leaves (Deglet Nour and Alig) by Kombucha Fermentation: Focus on Polyphenols, Antioxidant, Antidiabetic, and Cytotoxic Activities

The date palm, scientifically known as Phoenix dactylifera, is an important cultural and economic source of wealth in southern Tunisia. It produces considerable agricultural waste, including palm leaves, the disposal of which is often a challenge. Our study addresses the sustainable conversion of date palm leaves into a valuable product through kombucha fermentation, focusing on two widely used varieties in Tunisia: Deglet Nour and Alig. HPLC-RI analysis showed a significant difference in the fermentation process between the treated samples, which is reflected in the highest sugar consumption and metabolite production in Alig palm. Unfermented and fermented date palm leaves were sequentially extracted with solvents of increasing polarity (ethyl acetate and butanol) to evaluate their chemical composition and bioactivity. The results showed that kombucha fermentation significantly increased the total phenolic content, with the highest amounts in the ethyl acetate fraction. In terms of antioxidant activity, the ethyl acetate extracts showed a high percentage inhibitory activity (82.76 %) against the DPPH radical found in fermented Palm Alig, which also exhibited the most important antidiabetic capacity (resulting in an IC₅₀ value of 20 μg/mL). The chemical analyses resulted in the detection of 19 compounds by HPLC-DAD and 50 volatiles by GC-MS, which are mainly found in kombucha extracts.