Microbial Regulation of Deterioration and Preservation of Salted Kelp under Different Temperature and Salinity Conditions

Abstract

High salinity is an effective measure to preserve kelp, but salted kelp can still deteriorate after long-term preservation. In order to clarify the key conditions and microbial behavior of salted kelp preservation, 10% (S10), 20% (S20), and 30% (S30) salt concentrations were evaluated at 25 °C (T25) and 4 °C (T4). After 30 days storage, these salted kelps showed different states including rot (T25S10), softening (T25S20), and undamaged (other samples). By detecting polysaccharide lyase activity and performing high-throughput sequencing of the prokaryotic 16S rRNA sequence and metagenome, we found that deteriorated kelps (T25S10 and T25S20) had significantly higher alginate lyase activity and bacterial relative abundance than other undamaged samples. Dyella, Saccharophagus, Halomonas, Aromatoleum, Ulvibacter, Rhodopirellula, and Microbulbifer were annotated with genes encoding endonuclease-type alginate lyases, while Bacillus and Thiobacillus were annotated as the exonuclease type. Additionally, no alginate lyase activity was detected in undamaged kelps, whose dominant microorganisms were halophilic archaea without alginate lyase-encoding genes. These results indicated that room-temperature storage may promote salted kelp deterioration due to the secretion of bacterial alginate lyase, while ultra-high-salinity and low-temperature storage can inhibit bacterial alginate lyase and promote the growth of halophilic archaea without alginate lyase, thus achieving the preservation of salted kelp.

Assessment of Food Quality and Safety of Cultivated Macroalgae

“…Salting is another effective measure to preserve seaweeds. Wei et al [ 3 ] evaluated the effects of salt concentrations (10, 20, 30%) at 25 and 4 °C on microbial diversity and spoilage. They found that a salinity above 20% preserved several seaweed species even at room temperature storage, and refrigeration preservation at a salinity of 10% worked as well [ 3 ].…”

“…Wei et al [ 3 ] evaluated the effects of salt concentrations (10, 20, 30%) at 25 and 4 °C on microbial diversity and spoilage. They found that a salinity above 20% preserved several seaweed species even at room temperature storage, and refrigeration preservation at a salinity of 10% worked as well [ 3 ]. However, the high salt content may limit the further use in several products and the amount of seaweed that can be used without further processing.…”

Halorussus halobius sp. nov., Halorussus marinus sp. nov. and Halorussus pelagicus sp. nov., isolated from salted brown alga Laminaria

“…Halophilic micro-organisms derived from raw kelp or pickling salt would thus thrive in salted kelp. According to our previous results, salted Laminaria are inhabited by a dense population of haloarchaea [2]. Members of the haloarchaea require high salt concentrations for growth.…”

Brine-Processed Caulerpa lentillifera Macroalgal Stability: Physicochemical, Nutritional and Microbiological Properties

“…Salting is another effective method for preserving high-moisture foods and can be used as a stand-alone operation or for drying vegetables and other foods [17]. High salinity is an efficient method for preserving seaweed, but salted seaweed can still degrade during long-term storage [18]. Brine solutions protect the microbiological quality of fresh foods by lowering water activity, inducing hyperosmotic shock and altering the metabolism of spoilage and harmful microbes via direct lethal actions of the chloride ion [19,20].…”