The project investigated the feasibility of reducing sodium content in the traditional German fish product Matjes nordische Art by replacing conventional salt with a range of salt‑exchange substances. Thirteen different exchange agents were initially screened in sensory acceptance tests, and the five best‑performing materials were selected for further study. In the resulting product samples the added salt content was lowered by 35 % to 60 % compared with the commercial reference that contains 5 % NaCl. Because the final sodium level depends not only on the added brine but also on the raw fish and other ingredients, the overall sodium reduction in the finished product ranged from 29 % to 48 % relative to the standard formulation.

The five reduced‑salt samples were stored for four weeks at 3 °C under a protective atmosphere and were evaluated every few days by a trained panel of seven assessors following DIN 10967‑1. No statistically significant differences (p < 0.05) were found in appearance, aroma, taste or texture compared with the reference product, and no changes emerged over the storage period. A consumer survey of 61 untrained participants recruited via the University of Applied Sciences Hamburg, the Thünen Institute, the Fish Information Centre (FIZ) and the MRI Hamburg yielded average ratings of “slightly liked” or “liked somewhat” for all samples, with no significant preference for the reduced‑salt variants. The participants noted a slightly softer texture, bitterness and a strong saltiness in both the reduced‑salt and reference products, likely because the fish was served alone rather than with traditional accompaniments.

Analytical measurements during the storage trials showed no significant differences between the reduced‑salt and reference samples in texture (maximum compression force of 75 % of a 20 mm diameter, 9–13 mm high sample), colour (CIE L*a*b*), pH, or water activity. Histamine concentrations remained below the detection limit of 0.75 mg kg⁻¹ in all products. Microbiologically, aerobic and anaerobic mesophilic counts did not differ significantly between the groups. The dominant anaerobic flora in the reference product was Weissella viridescens, whereas Lactococcus lactis dominated the reduced‑salt samples; both are harmless lactic acid bacteria. Under aerobic conditions, Mannheimia haemolytica was present in all samples, also posing no health risk.

In vitro growth experiments in standard I‑broth at room temperature revealed that the salt‑exchange substances produced steeper growth curves for a mixed flora from Matjes nordische Art compared with pure NaCl, indicating a weaker inhibitory effect on bacterial proliferation. These preliminary results suggest that the exchange agents do not compromise the product’s safety profile.

The project was carried out in close collaboration with several partners. The fish samples were produced by Friesenkrone‑Feinkost Heinrich Schwarz & Sohn (Marne). Challenge tests with Listeria monocytogenes were performed at the KIN‑Lebensmittelinstitut (Neumünster), where Friesenkrone and the KIN also provided advisory support. The research team was supported by the University of Applied Sciences Hamburg, the Thünen Institute, the Fish Information Centre (FIZ) and the MRI Hamburg. Funding was provided by the German Federal Ministry for Economic Affairs and Energy (BMEL) under its Innovation Programme, which aims to strengthen the economic innovation capacity of the fish‑processing industry. The project’s timeframe covered the development, sensory and microbiological testing phases, with the four‑week storage trials conducted during the final experimental period. The results provide a scientific basis for the commercial development of sodium‑reduced fish products using salt‑exchange technology, potentially opening a new market segment and offering a competitive advantage to producers willing to adopt this approach.