Effect of pre-drying storage and drying method on the quality of dried kelp

Abstract

Farmed kelp (Alaria esculenta and Saccharina latissima) can be the future North Atlantic Ocean crop, in coastal areas of Greenland, the Faroe Islands, and Norway. One of the main bottlenecks in upscaling kelp production is stabilising the annual harvest before it spoils. Microbial quality changes were investigated during chilled storage of seven and ten days for fresh A. esculenta and S. latissima, respectively, and subsequent stabilisation by either convection (37.2 °C) or ambient temperature (range 5–10 °C) atmospheric drying. The quality of the dried kelps was determined by their swelling, water-, and lipid-binding capacity. Microbial loads (3 M Aerobic Count Plate) were 4.0–4.5 log(CFU/g_{wet weight}) at harvest time for the two species and increased to 5.9–6.1 log(CFU/g_{wet weight}) after seven days of storage at 2–3 °C. For fresh kelp, which was immediately dried, both drying processes had a limited impact on the bacterial loads, with reductions of 0.3 to 2.0 log(CFU/g_{corrected wet weight}) during the process. In contrast, the same drying process resulted in reductions of 4.2 to 5.1 log(CFU/g_{corrected wet weight}) for kelp, which had been stored for seven days before drying. Dried S. latissima showed significantly higher swelling and water-binding capacities than A. esculenta, regardless of the drying method. Drying at ambient temperature over three days yielded higher lipid-binding capacity for both species than convection drying. Based on the bacterial concentrations, the seaweed should be stabilised within the first five days of post-harvest chilled storage. Convection drying inactivates more bacteria and has a shorter process time (2.5 h). However, if the kelp is intended for use in a lipid-rich product like pesto, the slower ambient temperature drying might be beneficial.