Effect of O(2)-CO(2) enriched atmospheres on microbiological growth and volatile metabolite production in packaged cooked peeled gray shrimp (Crangon crangon).

This study evaluated the effect of modified atmospheres (MAs) with different O(2) concentrations on microbial growth and volatile metabolite production in gray shrimp (Crangon crangon) during storage at 4 °C. Eight MAs were evaluated in total. Four of the MAs evaluated were without CO(2): 0/0/100, 0/10/90, 0/30/70, 0/50/50 (% CO(2)/O(2)/N(2)) whilst the other four MAs all contained 50% CO(2): 50/0/50, 50/10/40, 50/30/20, 50/50/0 (% CO(2)/O(2)/N(2)). Volatile spoilage metabolites were identified by thermal desorption GC-MS and quantified during storage by selective ion flow tube mass spectrometry (SIFT-MS). In comparison to microbial growth observed with an atmosphere of 100% N(2), microbial growth was stimulated by the addition of O(2) in the MAP in the absence of CO(2.) Under these conditions the total psychrotrophic counts exceeded 7 log cfug(-1) after just 3 days of storage. However, in the presence of 50% CO(2) the total psychrotrophic count exceeded 7 log cfug(-1) after 5 days of storage. The combination of 50% CO(2) and 50% O(2) significantly inhibited microbial growth. For this MA condition, a diminishing effect on the production of metabolites was also observed, especially for amines and sulfur compounds, which constituted the major fraction of components causing the offensive odor.