Pentanal

Erythromycin was purchased from Tokyo Chemical Industry (Tokyo, Japan). NF-κB inhibitor, 5HPP-33, was purchased from Merck KGaA (Darmstadt, Germany). Acrolein, crotonaldehyde, dansyl hydrazine (DH), glyoxal, 2,4-decadienal (DDE), heptadecanal, hexadecanal, 2,4-nonadienal (NDE), octadecanal, 2-octenal, pentadecanal, tetradecanal and 2-undecenal were also purchased from Tokyo Chemical Industry (Tokyo, Japan). Acetaldehyde, p-Toluenesulfonic acid (p-TsOH) and the reactive carbonyl species (RCs), including propanal, pentanal, butanal, 2-hexenal, hexanal, 2-heptenal, heptanal, octanal, 2-nonenal, nonanal, decanal, undecanal, dodecanal and tridecanal, were obtained from Sigma-Aldrich (St. Louis, MO). 4-Hydroxy-2-hexenal (HHE), 4-hydroxy-2-nonenal (HNE) and 4-oxo-2-nonenal (ONE) were purchased from Cayman Chemical Company (Ann Arbor, MI). p-Benzyloxybenzaldehyde (p-BOBA) was purchased from Wako Pure Chemical Industries (Osaka, Japan). 8-Heptadecenal (8-HpDE), 8,11-heptadecadienal (8,11-HpDDE) and 8,11,14-heptadecatrienal (8,11,14-HpDTE) were synthesized using a previously described method.^{(10 (link),11 (link))} Secosterol-A and B were synthesized according to a procedure reported by Wentworth et al.^{(12 (link))} Stock solutions of the RCs and an internal standard (IS) (p-BOBA, 10 µM) were prepared separately in acetonitrile and stored at −20°C prior to use.

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.

Freeze-dried Finnish mushroom (Craterellus tubaeformis) was obtained from Lyotech Oy Co. Ltd. Company (Helsinki, Finland). The aroma compounds in the freeze-dried mushroom were extracted as essential oil by supercritical CO₂ (FLAVEX Naturextrakte GambH Co. Ltd., Rehlingen, Germany) for commercial purposes and the corresponding residues were used in this study. Cellulase produced by Novozyme Nordisk (Bagsvaerd, Denmark) was purchased from Novo Co., Ltd. (Shanghai, China). Neutral protease was purchased from Longda Bio-Products Co., Ltd. (Yishui, Shandong, China). 1,2-Dichlorobenzene and n-alkane mixtures were all chromatography grade and purchased from Sigma-Aldrich Co., Ltd. (Shanghai, China). Authentic standard compounds including 1-octen-3-ol, hexanal, heptanal, pentanal, nonanal, benzaldehyde, octanal, and 6-methyl-5-hepten-2-one were obtained from Sigma-Aldrich Co., Ltd. The other chemicals used were of analytical grade and were obtained from Shanghai Chemical Reagent Co. Ltd. (Shanghai, China).

All reagents utilized in this assay were of analytical quality. Sodium chloride (NaCl, 99.5%), and calcium chloride (CaCl₂, >99.0%) were obtained from Panreac (Spain, Barcelona). Ultrapure water was supplied from a Milli-Q^® system (Millipore); the 3-octanol used as internal standard and other VOCs for identification, namely, 1-butanol, 1-heptanol, 1-octanol, 1-propanol, (E)-2-hexenal, 2-methyl-butanal, 2-ethyl-1-hexanol, 2-methyl-1-propanol, 2-phenylethanol, acetaldehyde, benzaldehyde, ethanol, ethyl acetate, ethyl butanoate, ethyl decanoate, ethyl hexanoate, ethyl octanoate, ethyl propanoate, ethyl 3-hydroxybutanoate, hexyl acetate, and pentanal with purity up to 98% were acquired from Sigma Aldrich (Madrid, Spain). Helium gas purity of 5.0 (Air Liquide, Portugal) was utilized as the GC carrier gas. Solid-phase microextraction holder and divinylbenzene/carboxen/polydimethylsiloxane (DVB/CAR/PDMS) fiber were supplied from Supelco (Bellefonte, PA, USA). The Kovats index (KI) was calculated by the injection of a series of C₈ to C₂₀ straight-chain n-alkanes (at 40 mg L⁻¹ in n-hexane) produced by Fluka (Buchs, Switzerland).

Commercially available food additive products were used in the human sensory test. Food-grade NaCl was purchased from Naikaisyoji (Tokyo, Japan), and monosodium glutamate (MSG) was purchased from Ajinomoto Co., Inc. (Tokyo, Japan). All flavor compounds (of food additive grade), including propionaldehyde, butanal, isobutylaldehyde, 2-methylbutylaldehyde, pentanal, IVA, hexanal, heptanal, octanal, propionic acid, 2-methylbutyric acid, isovaleric acid, hexanoic acid, heptanoic acid, propyl alcohol, 2-methyl-1-butanol, hexanol, heptanol, methional, methionol, and 3-(methiylthiol) propionic acid, were purchased from Sigma-Aldrich (St. Louis. MO, USA). Deionized water for test solutions and mouth rinsing was supplied by a Mill-Q water purification system (Millipore, Bedford, MA, USA). γ-Glu-Val-Gly was obtained from Ajinomoto Co., Inc. (Tokyo, Japan). NPS-2143, a CaSR inhibitor, was synthesized, as described by Rybczynska et al. [41 (link)]. Chemicals for cell based-assays, such as CaCl₂, ethylenediaminetetraacetic acid (EDTA), and probenecid, were purchased from Sigma-Aldrich (St. Louis. MO, USA).