Effect of Salt and Sugar on Isolated <i>Rhizopus</i> sp. Growth and Volatile Signatures During Tuna Off-Cuts Fermentation

The valorisation of seafood processing side streams is a growing priority for sustainable food systems. Here, we investigated solid-state fermentation (SSF) of tuna off-cuts using Rhizopus sp. and evaluated the influence of glucose and NaCl on fungal growth and volatile organic compound (VOCs) production for 72 h at 30 °C. Ergosterol quantification confirmed that glucose supplementation enhanced fungal growth, while NaCl suppressed fungal proliferation, even under nutrient-enriched conditions. VOC profiling revealed that glucose promoted ester and fatty acid formation associated with fruity and creamy aroma notes, NaCl reduced these products and shifted metabolism toward fatty acids and aldehydes linked to fatty or green odors, and combined treatments yielded mixed outcomes. Multivariate analyses distinguished clear treatment clusters, highlighting the relationship between treatment-dependent growth and sensory-relevant VOCs. These findings demonstrate that simple additives can be used to modulate fermentation outcomes, providing a practical basis for the usage of fungal SSF for tuna side stream valorisation.