Model 5890 series 2

Aliquots (0.4 mL) from tubes were collected for SCFA analysis. Immediately after sampling, aliquots were mixed with 100 μL of the internal standard mixture (157.5 μL of 4-methylvaleric acid (nr 277827–5G, Sigma-Aldrich Inc., St. Louis, MO, USA), 1.47 mL of 85% phosphoric acid, 39 mg of copper sulfate pentahydrate) and the resulting blend was brought to 25 mL of final volume with purified water and 400 μL of copper sulphate solution (2.75 mg/mL) to halt fermentation. Samples were stored at −80 °C until analysis.
Defrosted samples were centrifuged at 3000× g for 10 min (Microfuge^® 20R, Beckman Coulter, Brea, CA) and 4 μL was prepared for injection into a gas chromatograph (model 5890 Series II, Hewlett Packard, Palo Alto, CA, USA) equipped with a fused silica capillary column (NukolTM, Supelco nr 40369-03A, Bellefonte, PA, USA) and a flame ionization detector (GC-FID 7890A, Agilent Technologies, Inc., Santa Clara, CA, USA). SCFA was assayed and identified as previously described [36 (link)] using acetate, propionate and butyrate relative to 4-methyl valeric acid as standards (Supelco, Bellefonte, PA, USA).

Plasma FA were analyzed as fatty acid methyl esters (FAMEs) by gas chromatography analysis. FA were extracted from plasma as previously described by Folch et al. with slight modifications [13 (link)]. Individual FAMEs were separated and quantified by gas chromatography using a Model 5890 Series II instrument (Hewlett-Packard, Palo Alto, CA, USA) equipped with a flame ionization detector and a fused silica capillary column SP-2560 (100 m length, 0.25 mm i.d., and 0.2-μm film thickness) (with heptadecanoic acid, 17:0, used as the internal standard). 1 μL of each sample was injected into the gas chromatography system.
The initial oven temperature was programmed to 140 °C for 5 min. Then, it increase to 240 °C at a rate of 4 °C / min. The injector and detector temperatures were 260 °C.
FAMEs were identified by comparing their retention times with those of individual standards used in mixture (Supelco 37 Component FAME Mix, Palo Alto, USA). The FA composition was reported as a relative percentage of the total peak area using a HP Chemstation integrator.

Hazelnut oil was purchased from a local manufacturer, and fatty acid methyl esters (FAMEs) from the oil samples were prepared as described by Issaoui et al. [23 (link)]. Individual FAMEs were separated and quantified by gas chromatography using a Model 5890 Series II instrument (Hewlett-Packard, Palo Alto, CA, USA) equipped with a flame ionization detector, and a DB-23 fused silica capillary column (60 m length, 0.32 mm i.d., 0.25 μm film thickness; HP-Agilent Technologies, Wilmington, DE, USA). Table 1 shows the fatty acid composition of the hazelnut oil used in this study.