title: Mesophilic and psychrotrophic bacteria from meat and their spoilage potential in vitro and in beef.
abstract: Mesophilic and psychrotrophic populations from refrigerated meat were identified in this study, and the spoilage potential of microbial isolates in packaged beef was evaluated by analyzing the release of volatile organic compounds (VOC) by gas chromatography-mass spectrometry (GC/MS). Fifty mesophilic and twenty-nine psychrotrophic isolates were analyzed by random amplified polymorphic DNA-PCR, and representative strains were identified by 16S rRNA gene sequencing. Carnobacterium maltaromaticum and C. divergens were the species most frequently found in both mesophilic and psychrotrophic populations. Acinetobacter baumannii, Buttiauxella spp. and Serratia spp. were identified among the mesophilic isolates, while Pseudomonas spp. were commonly identified among the psychrotrophs. The isolates were further characterized for their growth at different temperatures and their proteolytic activity in vitro on meat proteins extracts at 7 degrees C. Selected proteolytic strains of Serratia proteamaculans, Pseudomonas fragi, and C. maltaromaticum were used to examine their spoilage potential in situ. Single strains of these species and mixtures of these strains were used to contaminate beef chops that were packed and stored at 7 degrees C. At time intervals up to 1 month, viable counts were determined, and VOC were identified by GC/MS. Generally, the VOC concentrations went to increase during the storage of the contaminated meats, and the profiles of the analyzed meat changed dramatically depending on the contaminating microbial species. About 100 volatiles were identified in the different contaminated samples. Among the detected volatiles, some specific molecules were identified only when the meat was contaminated by a specific microbial species. Compounds such as 2-ethyl-1-hexanol, 2-buten-1-ol, 2-hexyl-1-octanol, 2-nonanone, and 2-ethylhexanal were detectable only for C. maltaromaticum, which also produced the highest number of aldehydes, lactones, and sulfur compounds. The highest number of alcohols and ketons were detected in the headspace of meat samples contaminated by P. fragi, whereas the highest concentrations of some alcohols, such as 1-octen-3-ol, and some esters, such as isoamyl acetate, were produced by S. proteamaculans. In conclusion, different microbial species can contribute to meat spoilage with release of different volatile compounds that concur to the overall quality decrease of spoiling meat.
authors.affiliation: Department of Food Science, School of Biotechnological Sciences, University of Naples Federico II, Via Università 100, 80055 Portici, Italy.
authors.forename: Danilo
authors.initials: D
authors.lastname: Ercolini
authors.forename: Federica
authors.initials: F
authors.lastname: Russo
authors.forename: Antonella
authors.initials: A
authors.lastname: Nasi
authors.forename: Pasquale
authors.initials: P
authors.lastname: Ferranti
authors.forename: Francesco
authors.initials: F
authors.lastname: Villani
mesh_terms: D015169:Colony Count, Microbial; D016172:DNA Fingerprinting; D004269:DNA, Bacterial / Q000235:genetics; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005511:Food Handling / Q000379:methods; D008401:Gas Chromatography-Mass Spectrometry; D006090:Gram-Negative Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D008460:Meat / Q000032:analysis* / Q000382:microbiology*; D050296:Microbial Viability; D010802:Phylogeny; D011506:Proteins / Q000378:metabolism; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D019105:Random Amplified Polymorphic DNA Technique; D012034:Refrigeration; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D013997:Time Factors; D055549:Volatile Organic Compounds / Q000032:analysis*
chemical_list: D004269:DNA, Bacterial; D004275:DNA, Ribosomal; D011506:Proteins; D012336:RNA, Ribosomal, 16S; D055549:Volatile Organic Compounds