Diversity and characterization of spoilage-associated psychrotrophs in food in cold chain

In this work, psychrotrophs known to cause food spoilage were isolated from commercial food products. Further, temperature sensitivities and volatile organic compounds of the representative strains were characterized to evaluate the population heterogeneity. A total of 490 isolates belonging to 38 genera of 20 families were identified from 30 psychrotroph-positive samples, among which Gram-negative bacteria occurred frequently. The genus Pseudomonas exhibited a clear predominance, especially Pseudomonas fragi, followed by Psychrobacter, Brochothrix, Serratia, and Stenotrophomonas, with the dominant bacteria varying with origin. Aquatic products related to Hafnia and quick-frozen food corresponding to Stenotrophomonas, as well as livestock products were shown to be good ecological niches for growth of psychrotrophs. The genus Pantoea was shown to have an intimate relationship with fruits. While in bean, cereal grain and dairy products, only Pseudomonas was present. The fits of the growth curves demonstrated good adaptability and tolerance of the tested strains under 4 °C, and multifarious growth also reflected intra-species differences and phenotypic diversity. Various kinds of esters, aromatic compounds, alcohols, and ketones were frequently detected by GC-MS. High alcohols were seen in Psychrobacter, but hydrocarbons and ethers were more often found in Pseudomonas. In particular, since high amounts of isophorone were only discovered in bacteria samples, it is speculated to be the characteristic substance of psychrotrophs.