Methods for iodine-reduction of sugar kelp to produce safe, flavourful and nutritious ingredient to the food industry

The Norwegian seaweed sector based on cultivated kelp biomass (mostly the sugar kelp S. latissima) is growing rapidly. The high iodine content of S. latissima is a major challenge hampering the commercial development of food products containing kelp ingredients. During this project, the production and quality of iodine-reduced S. latissima and its potential as a food ingredient for the Nordic food industry was investigated. The objectives of the project were to i) identify processing methods to provide safe, nutritious and tasty ingredients from sugar kelp and ii) test one or more iodine-reduced ingredients from S. latissima in a commercial product from the food industry.

 

Both established (blanching with freshwater) and new methods (e.g. steam treatment, use of rotavapor, seawater blanching) were tested on either fresh, fermented or frozen/thawed biomass. Due to large variations in the iodine content of the start material of the different experiments, it has been difficult to achieve predictably low iodine content below 2000 mg/kg (dry weight, DW). Significant iodine reduction was only achieved by the addition and subsequent removal of liquid during the process. In contrast, no iodine reduction was achieved in processes where the liquid (i.e. added water and/or drip loss) was retained. This indicates that there is no evaporation of iodine (mainly present in the form of water-soluble iodide) under the tested conditions. Sufficient iodine reduction below 2000 mg/kg DW was achieved by the combination of seawater blanching and fermentation (850 mg/kg DW) suggesting that the iodine content reduction is mainly due to the iodide in the kelp leaching in the surrounding liquid. The analysis of additional seawater-blanched samples under commercial production settings involving a larger volume of seawater revealed an even lower iodine content (190 mg/kg DW). These results indicate that blanching using salt water has the potential to reduce the iodine content in S. latissima to safe levels for food applications. The kelp-to-water ratio (either fresh- or seawater) may be an important factor determining the extent of iodine- reduction during the process. Seawater-blanching both with and without subsequent fermentation limited dry matter (i.e. nutrient) losses compared to blanching in freshwater even though loss of minerals (especially potassium) was observed. This processing method will be investigated further in a second-stage research project.

 

The sensory properties (flavour/aroma and texture) of a selection of S. latissima ingredients were evaluated using a trained panel. Significant differences were measured among steam-treated, freshwater and seawater-blanched samples, as well as seawater-blanched then fermented, and A. esculenta samples (used as reference). All samples, except freshwater-blanched, had a fairly distinct umami flavour. This indicates that water-soluble flavour components (e.g. monosodium glutamate) are better retained in seawater-blanched samples compared to freshwater-blanched material. A product prototyping experiment demonstrated that the use of kelp ingredients even at low inclusion level (0.5 % of a portion) makes a significant contribution to the flavour of a typical commercial food product (dehydrated spinach soup). Specifically, the ingredients (fermented and seawater-blanched) contributed with saltiness highlighting their potential as salt replacement in the food industry.