The total volatile basic nitrogen fraction (TVB-N) is often used as a quality parameter in the fish industry to assess spoilage. This parameter often leads to discussions between producers and retailers when it comes to defining clear limits of acceptability for modified atmosphere (MA) packed fish and fishery products. Suggested product limits (mg N/100 g fish) do not always correlate with the presence of off-odors. Gray shrimp are an economic valuable, very perishable niche product, where the TVB-N fraction plays an important role considering its shelf life. This research focuses on the effect of a shrimp matrix and its pH on the volatilization of these formed bases, revealing the relationship between concentrations in the fishery product and the concentrations of these bases present in the headspace of the packed product. Especially, the pH of the product, which is lowered when fishery products are packed under a carbon dioxide enriched atmosphere, appeared to have an immense effect on the volatilization of these bases. The effect of the fish matrix itself is established by means of calculated equilibration constants (dimensionless) being 2.13 x 10(-4) +/- 0.38 x 10(-4) for trimethylamine, 6.34 x 10(-5) +/- 1.71 x 10(-5) for dimethylamine, and 2.58 x 10(-5) +/- 0.49 x 10(-5) for ammonia. Comparison of these constants with the equilibration constants of an aqueous solution indicated the retention of these bases in the product. This article provides not only the important insights for the interpretation of TVB-N values in modified atmosphere packaged gray shrimp but also the methodology to extend these findings to other fish and fishery products.