Ethnographic heritage, fermentation dynamics, and mechanism-based functional potential of legen (Borassus flabellifer) from East Java, Indonesia: a narrative review

Legen, a traditional palm sap beverage derived from Borassus flabellifer in East Java, Indonesia, represents a unique convergence of cultural heritage, ecological adaptation, and emerging functional food potential. This review synthesizes current knowledge on its ethnographic significance, processing practices, nutritional composition, fermentation microbiology, and mechanism-based health implications. Legen is deeply embedded in local food systems, serving both as a daily refreshment and a sociocultural symbol. Compositionally, it is characterized by high levels of readily available carbohydrates, essential minerals, and bioactive compounds, including phenolics and flavonoids that contribute to antioxidant capacity. Spontaneous fermentation by lactic acid bacteria and yeasts drives biochemical transformations that influence sensory attributes, microbial stability, and the formation of metabolites with potential physiological relevance. Mechanistic evidence suggests that these compounds may modulate oxidative stress and inflammatory pathways, although such effects are primarily supported by in vitro and in vivo studies rather than human clinical trials. Significant challenges remain, particularly regarding variability in ethanol content, microbial safety, and the absence of standardized processing practices. These limitations constrain broader utilization and highlight the need for improved quality control and evidence-based validation. Future research integrating controlled fermentation, multiomics approaches, and human studies is essential to substantiate functional claims. Legen thus emerges as a promising traditional beverage with potential relevance to contemporary food systems, provided that safety, standardization, and scientific validation are rigorously addressed.