μm dvb carboxen pdms

Sample preparation for volatile and aroma identification used the same methods as previously described [10 (link)]. Briefly, 3 mL juice was mixed with the same volume of saturated sodium chloride solution (359 g/L), and an internal standard 3-hexanone with a final concentration of 10 μM. The mixture was prepared in a 20 ml glass vial and sealed with a silicone/PTFE septum. The vials were stored at − 20 °C until analyzed. For analysis, juice samples were incubated for 30 min at 40 °C, and a 2.0 cm solid phase microextraction (SPME) fiber (50/30 μm DVB/Carboxen/PDMS; Supelco, Bellefonte, PA) was used to extract the volatiles. Volatiles were analyzed by a GCMS (Model 6890/5973 N, Agilent, Santa Clara, CA) with a DB5 column (60-m length, 0.25-mm i.d., 1.00-μm film thickness). The program settings were according to the report [10 (link)]. Volatile compounds were identified by comparing their mass spectra with the authorized standard chemicals, the NIST mass spectral database, and published retention indices. The amount of each aroma volatile was expressed as relative content (aroma volatile peak area over internal standard peak area).

Volatile compounds in all the wine samples were extracted using headspace solid-phase microextraction (HS-SPME). A 5 mL wine sample and 1 g of NaCl were placed in a 15 mL sample vial, which contained a magnetic stirrer (1 cm) and 10 μL internal standard 4-methyl-2-pentylalcohol (1.0018 g/L, Sigma-Aldrich, Milwaukee, WI, USA). The vial was tightly capped with a polytetrafluoroethylene (PTFE) -silicon septum, heated at 40 °C for 30 min on a heating platform, and agitated at 400 rpm. The solid-phase microextraction (SPME) (50/30-μm DVB/Carboxen/PDMS, Supelco, Bellefonte, PA, USA), preconditioned according to the manufacturer’s instructions, was then inserted into the headspace, where extraction was allowed to occur for 30 min with continued heating and agitation via a magnetic stirrer. The volatiles from the fiber were subsequently desorbed by injecting the fiber into the gas chromatography (GC) injector for 8 min [44 (link)].

For each subsample, 5 mL of the juice, 1.00 g of NaCl, and 10 μL of 4-methyl-2-pentanol (internal standard, 1.0018 g L^-1) were mixed in a 15-mL airtight vial containing a magnetic stirrer. Head space-solid phase microextraction (HS-SPME) was used for free volatile compound extraction according to our previous studies [20 (link)]. In brief, the vial containing the sample was equilibrated at 40°C for 30 min with agitation. Then, the pretreated SPME fiber (50/30-μm DVB/Carboxen/PDMS, Supelco, Bellefonte, PA., USA) was inserted into the headspace for 30 min. Afterwards, the fiber was instantly desorbed in the GC injector for 8 min.

A 2 cm tri-phase SPME fiber (50/30 μm DVB/Carboxen/PDMS, Supelco, Bellefonte, PA, USA) was used to collect and concentrate volatiles prior to running on an Agilent 6890 GC coupled with a 5973 N MS detector (Agilent Technologies, Palo Alto, CA, USA). Before analysis, samples were held at 4°C in a Peltier cooling tray attached to a MPS2 autosampler (Gerstel). All other volatile sampling and analysis methods were as previously described [15 ]. The volatile 3-hexanone was used as an internal control. An authentic γ-D standard (Sigma Aldrich, St. Louis, MO, USA) was run under the same chromatographic conditions as berry samples for verification of volatile identify. The area of each γ-D peak was normalized to the peak area of the internal standard, and normalized peak areas were compared between samples.