Multi-cycle Deodorization of Kelp (Laminaria japonica) Using Yeast-Immobilized Membranes: Kinetics and Stability of Key Off-flavor Degradation

The persistent fishy odor in kelp ( Laminaria japonica ) has significantly hindered its industrial applications. Although biofermentation serves as a common deodorization method, its non-reusable nature remains a notable limitation. This study investigated the precise degradation kinetics of key fishy compounds in kelp by a yeast immobilization system during five consecutive fermentation rounds. Under optimized conditions (3.8 h, 33°C, yeast inoculation 0.58 g/kg) in the immobilization system, the first round of kelp fermentation (KF1) achieved a sensory score of 90.3. Scanning electron microscopy (SEM) results indicated that the structural integrity of the yeast and the fiber membrane remained well-preserved during the first three cycles. However, a progressive flattening of both the yeast and the membrane structure was observed after the fourth and fifth cycles. Gas Chromatography-Mass Spectrometry/Odor Activity Value (GC-MS/OAV) analysis revealed that after the first fermentation round, the OAVs of critical fishy compounds 1-octen-3-one and ( E )-2-nonenal decreased significantly by 69.43% and 72.55%, respectively. Even after five round of kelp fermentation (KF5), their OAVs remained low, showing sustained reductions of 31.12% and 69.58% compared to the unfermented (UF) control. Further Partial Least Squares Discriminant Analysis (PLS-DA) identified 1-octen-3-one, ( E )-2-nonenal, and decanal as key fishy markers. These results demonstrate that the immobilization system maintains efficient multi-cycle deodorization, significantly reducing the contribution of key fishy compounds, thereby providing a critical foundation for developing recyclable and stable kelp processing technologies.