Volatile organic compounds from microalgae: sources, chemical diversity, biosynthesis, and bioactive potential.

Microalgae are prolific producers of volatile organic compounds (VOCs) that play important roles in atmospheric chemistry, aquatic ecosystem dynamics, and water quality, particularly through the generation of off-flavours and odors. Despite their ecological relevance and growing biotechnological interest, microalgal VOCs remain comparatively underexplored. These low-molecular-weight metabolites encompass a broad range of chemical classes, including terpenoids, sulfur-containing compounds, benzenes, furans, alkanes, alcohols, ketones, aldehydes, and esters. Knowledge of their chemical diversity, biosynthetic pathways, allelopathic effects, and other ecological functions is still not fully reviewed. This review synthesizes current understanding of microalgal VOCs, emphasizing how morphology, physiology, ecological niche, and genetic variability influence VOCs production. Commonly reported VOCs such as geosmin, methylisoborneol, β-cyclocitral, and 2-pentylfuran are discussed with respect to their occurrence, chemistry, ecological roles, regulation by biotic and abiotic factors, and impacts. Despite their diverse ecological and biochemical roles, limited elucidation of their biosynthetic mechanisms also highlighted. Microalgal VOCs exhibit diverse bioactivities, including antibacterial, antifungal, insecticidal, antioxidant, antiviral, and antiprotozoal properties, underscoring their potential for biotechnological and industrial applications. Advances in analytical approaches, particularly gas chromatography-mass spectrometry and electronic nose technologies, have significantly improved VOCs detection and profiling. This review identifies critical knowledge gaps and underscores the need for integrative studies to unravel the diversity, chemical structures, biosynthetic pathways, and ecological significance of microalgal VOCs, thereby enabling theirsustainable exploitation and facilitating their industrial applications.