Salt-pickling prolongs refrigerated shelf-life of sugar kelp (Saccharina latissima)

Sugar kelp (Saccharina latissima) is an edible brown macroalgae. Freshly harvested kelp has a short shelf-life unless immediately preserved. This, in combination with a short harvest period, creates a bottleneck for kelp-producing companies. The aim of this study was to investigate salt-pickling (0 [control], 5, 10, 15, 20, and 50% NaCl w/w) as a low-energy intensive post-harvest treatment to prolong shelf-life of sugar kelp during storage at 4.2 °C ± 1.0 °C for 364 days. The salt-pickled kelp was evaluated regarding physicochemical, sensory (odour acceptance), and microbial qualities during storage. The initial water activity (a_w) of fresh sugar kelp at 0.99 was reduced to stable a_w levels of 0.94, 0.86, 0.85, 0.81, and 0.75 by treatments with 5, 10, 15, 20, and 50% NaCl, respectively. Regardless of NaCl%, salt-pickling reduced the iodine content of kelp by 45-73%. While untreated samples developed noticeable off-odours after 6 days (score ≥ 2, out of 3), all salt-pickled samples remained acceptable (i.e., no off-odours) for at least 150 days. Addition of ≥15% NaCl decreased initial bacterial counts from 5.5 to ∼1.5 log₁₀(CFU/g), while 5% and 10% NaCl reduced counts to 4 and 2 log₁₀(CFU/g), respectively. Identification of isolates showed dominance of spore-forming bacteria in salt-pickled sugar kelp after 364 days, regardless of NaCl%. Sequencing indicated growth in low-salt (5-15%) samples while bacterial communities in high-salt (20-50%) samples resembled those in fresh kelp, indicating no change over 200 days. Results from this study support industrial application of salt-pickling for long-term preservation of sugar kelp.