Volatolomics reveals the influence of O2/CO2 on the growth of Pseudomonas fragi and its volatile metabolites on meat substrates.

Pork is highly susceptible to microbial spoilage. The growth and metabolism of spoilage bacteria cause the formation of malodorous volatile organic compounds (VOCs), leading to sensory decline. Even though the atmosphere is a well-known extrinsic factor affecting microbial growth, the fundamental impact of bulk gas ratios on VOC production still needs to be further elaborated. The present research focuses on Pseudomonas fragi, one of the most dominant spoilage microbes in packaged meat, by studying its behavior as influenced by atmospheres. Solid pork simulation media inoculated with a pure meat-derived P. fragi strain were stored under four conditions with different bulk gas ratios (v/v% O2/CO2/N2: air, 0/0/100, 20/20/60, 20/40/40). For each atmosphere, characteristic microbial VOCs were identified by combining online and offline chemical analytical tools, namely selected-ion flow-tube mass spectrometry (SIFT-MS) and thermal-desorption gas chromatography mass spectrometry (TD-GC-MS). In total, fourteen compounds were linked to the investigated P. fragi strain, including methyl acetate, ethyl acetate, methyl mercaptan, and dimethyl sulfide. Despite slower microbial growth under 0/0/100 and 20/20/60 when compared to air, anaerobic metabolites including sulfur-containing compounds and ethyl acetate were produced in high quantities at a lower microbial level. On the contrary, 40% CO2 largely limited bacterial counts and VOCs. Overall, comprehensive volatolome analysis provides informative insights into the P. fragi metabolism and its relation with the atmosphere, thus improving the understanding of meat spoilage mechanisms.