7890a instrument

VOCs were identified and quantified using HS-SPME/GC-MS. Raw milk (10 mL) and 20 μL internal standard (100 mg/kg) were placed in vials. The samples were equilibrated for 30 min in a 40 °C-water bath and stirred constantly. Fiber (1 cm) coated with divinylbenzene/carboxen/poly-dimethylsiloxane (50/30 μm) was used in the extraction. Then, the adsorption time was 30 min after inserting the SPME extraction fiber into the headspace vial. Subsequently, the sampler was removed from the headspace vial and inserted into the GC injector. The aroma compounds adsorbed on the SPME fiber were desorbed by heating (250 °C), and the desorption time was 5 min. GC-MS was performed using an Agilent 7890A instrument coupled to an Agilent 5975C mass selective detector and a DB-WAX UI column (30 m × 0.25 mm × 0.25 μm). The initial temperature was 30 °C, which was kept for 6 min, increased to 220 °C at 5 °C/min, and kept at 220 °C for 3 min. The entire process was carried out in full scan mode. For accuracy, three replicate analyses were conducted for each sample.
Retention index (RI) values for each VOC were calculated from GC-MS results for n-alkanes under similar conditions. The NIST 08 library was used to identify unknown compounds. Quantification was achieved using internal standards.

Optical rotations were measured on a JASCO P2000 automatic digital polarimeter. UV spectra were recorded on a JASCO V-650 spectrophotometer. IR spectra were recorded on a Nicolet 5700 spectrometer using an FT-IR microscope transmission method. NMR spectra were acquired with Bruker AVIIIHD 600, VNS-600, or Mercury-400 spectrometers in DMSO-d₆. HRESIMS spectra were collected on an Agilent 1100 series LC/MSD ion trap mass spectrometer. MPLC system was composed of two C-605 pumps (Büchi), a C-635 UV detector (Büchi), a C-660 fraction collector (Büchi), and an ODS column (450 mm×60 mm, 50 μm, 400 g; YMC). Semi-preparative HPLC was conducted using a Shimadzu LC-6AD instrument with an SPD-20A detector and a Daicel Chiralpak AD-H column (250 mm×10 mm, 5 μm). Preparative HPLC was also performed on a Shimadzu LC-6AD instrument with a YMC-Pack ODS-A column (250 mm×20 mm, 5 μm). Column chromatography (CC) was performed with silica gel (200–300 mesh, Qingdao Haiyang Chemical Inc., Qingdao, China), SF-PRP 512 A (100–200 mesh, Beijing Sunflower and Technology Development Co., Beijing, China), ODS (50 μm, YMC, Japan), and Sephadex LH-20 (GE, Sweden). TLC was carried out on glass precoated silica gel GF254 plates. Spots were visualized under UV light or by spraying with 10% sulfuric acid in EtOH followed by heating. GC analyses were obtained using an Agilent Technologies 7890A instrument.