2 methyl 3 heptanone

The following compounds, 2-methylpropanal, 2,3-butanedione, 3-methylbutanal, methional, 2-acetylfuran, 1-octen-3-one, 1-octen-3-ol, (E)-2-nonenal, (E,Z)-2,6-nonadienal, 2-acetylpyrazine, 2-acetyl-2-thiazoline, 2-ethyl-3,5(and 6)-dimethylpyrazine, (E,E)-2,4-decadienal, 1-hexanol, 2-phenylethanol, salicylaldehyde, p-vinylguaiacol, ethyl nonanoate, and ethyl octanoate were purchased from Sigma Aldrich (St. Louis, MO, USA). 2-Ethyl-3,5-dimethylpyrazine and 2-ethyl-3,6-dimethylpyrazine were separated using preparative GC and [²H₃]-2-Acetyl-1-pyrroline and [²H₄]-2-acetyl-2-thiazoline were synthesized as previously described [37 (link)]. 3-Methyl-1-butanol, guaiacol, and 2-methyl-3-heptanone were purchased from Tokyo Chemical Industry (TCI; Portland, OR, USA). 2,3-Diethyl-5-methylpyrazine, butylated hydroxytoluene (BHT), ethanol (200 proof) and dichloromethane were purchased from Fisher Scientific (Pittsburgh, PA, USA). Sodium bicarbonate and anhydrous sodium sulfate were purchased from Avantor (Center Valley, PA, USA).

A multi-purpose sampler (MPS 2XL, Gerstel GmbH & Co. KG, Mülheim, Germany) equipped with the 50/30 μm divinylbenzene/Carboxen™/polydimethylsiloxane (DVB/CAR/PDMS) solid-phase microextraction (SPME) fiber (Supelco Inc., Bellefonte, PA, USA), was employed to extract the volatiles from the headspace of red raspberry juice [9 (link)]. For each sample, 7 mL of the clear accurately pipetted into a 20 mL headspace vial (ANPEL Laboratory Technologies Inc., Shanghai, China), followed by addition of 2.52 g of NaCl (Sinopharm Chemical Reagent Co., Ltd., Shanghai, China) and 50 μL of 2-methyl-3-heptanone (8.16 μg/mL in methanol, Tokyo Chemical Industry Co., Ltd., Tokyo, Japan) as an internal standard. The automatic sampling procedure was as follows: sample was incubated at 45 °C for 10 min to reach equilibrium with shaking at regular intervals (20 s on, 2 s off); 2 cm of DVB/CAR/PDMS SPME fiber was introduced to the headspace environment, followed by the adsorption of volatiles at 45 °C for 40 min; the SPME fiber was inserted into the injection port of a gas chromatography–mass spectrometric (GC–MS) system, followed by the desorption of volatiles at 250 °C for 5 min.