The metabolomics analysis was performed based on a combined platform of GC–MS and LC–MS/MS to obtain a comprehensive metabolic profiling of S. Enteritidis. For GC–MS, different volumes of water were added to each sample to obtain a final bacterial concentration of 4 × 108 CFU/mL. After vortexing, 200 μL of the homogenate was transferred to a 2 mL Eppendorf tube, respectively. Afterward, 800 μL of methanol/acetonitrile (1:1, v/v), containing ribitol (Sigma-Aldrich, St. Louis, Missouri) as the internal standard (IS) was supplemented, followed by grinding in a 35-Hz grinder (JXFSTPRP-24, Jingxin Industrial Development Co., Ltd., Shanghai, China) for 4 min and sonication in ice-water for 5 min. After three repetitions, the samples were kept at −40°C for an hour and then centrifuged at 12,000 rpm at 4°C for 15 min. The supernatant was carefully removed from the tube and dried in a vacuum concentrator.
The extracts were derivatized before GC–MS analysis. The extracts were blended with 30 μL of methoxyamine hydrochloride (Tokyo Chemical Industry Co. Ltd., Japan), diluted in pyridine to 20 mg/mL, and maintained at 80°C. After 30 min incubation, 40 μL Bis (trimethylsilyl) trifluoro acetamide (BSTFA) with 1% Trimethylchlorosilane (TMCS)(v/v) (Regis Technologies, Inc., Morton Grove, United States) was added to each sample. Then, the mixture was sequentially incubated at 70°C for 1.5 h for later analysis.
The extracts were derivatized before GC–MS analysis. The extracts were blended with 30 μL of methoxyamine hydrochloride (Tokyo Chemical Industry Co. Ltd., Japan), diluted in pyridine to 20 mg/mL, and maintained at 80°C. After 30 min incubation, 40 μL Bis (trimethylsilyl) trifluoro acetamide (BSTFA) with 1% Trimethylchlorosilane (TMCS)(v/v) (Regis Technologies, Inc., Morton Grove, United States) was added to each sample. Then, the mixture was sequentially incubated at 70°C for 1.5 h for later analysis.
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