2 methyl 3 heptanone

Defatted soybean meal was purchased from Shandong Yuwang Ecological Food Industry Co., Ltd. (Dezhou, China). Iota-carrageenan was purchased from MSC Co., Ltd. (Yangsan City, Korea). 2-methyl-3-heptanone was purchased from Sigma-Aldrich (Shanghai, China). Commercial lyophilized yogurt starter culture, composed of Streptococcus thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB), was purchased from Danisco-DuPont (Shanghai, China). The other chemicals were all of analytical grade and purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

The following liquid substances were purchased from Sigma-Aldrich: 2-pentanone (98%), 3-pentanone (99%), 2-hexanone (98%), 3-hexanone (98%), 3-heptanone (analytical standard), 4-heptanone (98%), 2-nonanone (99%), 3-nonanone (99%), 2-decanone (98%), cyclohexanone (99.8%), 3-methyl-2-pentanone (99%), 2-methyl-3-pentanone (97%), 2-methyl-3-hexanone (98%), and 2-methyl-3-heptanone (99%). 2-butanone (99.5%), 2-heptanone (98.5%), and 3-methyl-2-butanone (98.5%) were purchased from Honeywell. 3-octanone (99%) and 3-decanone (97%) were purchased from Acros Organics and SAFC, respectively. These were used with no further purification.

N-Alkanes (C₆–C₃₀) used for the linear retention index (LRI) calculation were obtained from Sigma-Aldrich (Saint louis, MO, USA). All reference standards for qualitative and quantitative analyses of aromatic compounds (Table 2) were purchased from Sigma-Aldrich, Aladdin Reagents (Shanghai, China) and J&K Chemicals (Beijing, China). Hexane (HPLC grade) served as the solvent for dissolving reference standards, and 2-methyl-3-heptanone (internal standard (IS)) was purchased from Sigma-Aldrich. Sodium chloride was used for volatile extraction and other reagents were purchased from Huihai Scientific Instruments (Beijing, China).

Skim milk powder was collected from a local dairy company, and the same batch was used for the production of all FFMPs. Antioxidant-free refined sunflower oils were purchased from a local store (SuperValu, Dublin, Ireland), and stored in closed containers, in the dark under refrigeration (4 °C) until use.
1,1,3,3-tetraethoxypropane (TEP), trichloroAcetic acid (TCA), starch, potassium iodide, 37% hydrochloric acid (HCl), isooctane, BHA, BHT, rosmarinic acid, 1-pentanol, 2-heptanone, 2-pentanone, 3-octen-2-one, 2, 4-decadienal, hexanal, heptanal, octanal, pentanal, 2-nonenal (E), acetone, 2-nonanone, undecanal 2-methyl-4-pentanol, 2-methyl-3-heptanone, isovaleraldehyde and ethyl butyrate were purchased from Sigma-Aldrich (now Merck, Wicklow, Ireland), whereas carnosol and carnosic acid were obtained from Extrasynthese (Extrasynthese Co., Genay Cedex, France). Thiobarbituric acid (TBA) and sodium thiosulfate were obtained from VWR (VWR International Ltd., Dublin, Ireland). Isopropanol (PrOH) was acquired from Romil (Lennox Laboratory Supplies LTD, Dublin, Ireland) and n-hexane from Honeywell (Honeywell, Dublin, Ireland). Acetic acid was obtained from AppliChem GmbH (Darmstadt, Germany). Milli-Q^® water (H₂O) (18 mΩ) (Merck Millipore, Molsheim, France) or deionized H₂O was used throughout the experiments.

The standards of FAAs, 5′-nucleotides, methanol, potassium dihydrogen phosphate, and 2-methyl-3-heptanone were purchased from Sigma-Aldrich (Sigma-Aldrich, St. Louis, MO, USA). The reagents used in this paper were >99% pure. All the other chemicals used were of analytical grade, purchased from Sinopharm Chemical Reagent Beijing Co. Ltd., (Beijing, China).

Chromatography standards, including 2-methyl-3-heptanone (purity > 99%), n-alkanes (C₇–C₃₀) (purity > 99%), n-hexane (purity > 99%) and n-pentane (purity > 99%), were purchased from Sigma-Aldrich (St. Louis, MO, USA). Analytical reagents, including diethyl ether (purity > 99%), n-pentane (purity > 99%) and anhydrous sodium sulfate (purity > 99%) were provided by Yifengtiancheng Scientific Instruments Co. Ltd. (Beijing, China). Nitrogen (purity > 99.99%) was supplied by Beijing Haipubeifen Gas Industry Co. Ltd. (Beijing, China)

Wheat alkylresorcinols were prepared according to the method reported in our previous study (Liu et al., 2018). Wheat flour (10.5% protein, 1.7% fat, and 75.5% carbohydrates) were purchased from Beijng Er Shang Group (Beijing, China). Baker's yeast was obtained from Angel Yeast (Hubei, China). 2‐Methyl‐3‐heptanone were obtained from Sigma Aldrich (St. Louis, Mo, USA). Nε‐(carboxymethyl)lysine was purchased from J&K Scientific Ltd. (Beijing, China).