Succinic acid

The following reagents from Sigma–Aldrich (St. Louis, MI, USA) (purity ≥ 99%) were used: glucose, fructose, sucrose, stachyose, mannitol, citric acid, malic acid, tartaric acid, lactic acid, succinic acid, acetic acid, ascorbic acid, DPPH, TPTZ (2,4,6-tripyridyl-S-triazine), ABTS, Folin-Ciocalteu, Trolox, gallic acid, protocatechuic acid, theobromine, paraxanthin, epigallocatechin, catechin, epicatechin, quercetin, caffeine, caffeine, rutin, kaempferol, chlorogenic acid, p-coumaric acid, ferrulic acid, synapic acid, myricetin, and trigonelline. Acetonitrile (HPLC-grade) was obtained from J.T. Baker (Avantor, Radnor, Pennsylvania). Ethanol and other reagents were obtained from Merck (Darmstadt, Germany). Ultrapure water (Simplicity 185, Millipore, MA, USA) was used for the extractions and standard solutions.

Malic acid (99.5 %), succinic acid (99.5 %), citric acid (99.5 %), glucose (99.5 %), fructose (99 %), and sucrose (99.5 %) were purchased from Sigma-Aldrich (Budapest, Hungary) to determine the quantity of organic acids and sugars with high-performance liquid chromatography (HPLC) methods.
Chemicals for the determination of polyphenol, and antioxidant content were anhydrous sodium carbonate (99 %, Riedel-de Hӓen, Seelze, Germany), Folin-Ciocalteu reagent (98 %, Sigma-Aldrich, Budapest, Hungary), 2–4-6-tripyridyl-s-triazine (TPTZ) (98 %, Sigma-Aldrich, Budapest, Hungary), acetic acid (96 %, Reanal, Budapest, Hungary), anhydrous iron chloride (98 %, Merck, Budapest, Hungary), ascorbic acid (96 %, Sigma-Aldrich, Budapest, Hungary), and gallic acid (98 %, Sigma-Aldrich, Budapest, Hungary).

The mitochondrial respiration medium MiR05 (pH 7.1 at 37 °C) included 0.5 mM ethylene glycol-bis(2-aminoethyl ether)-N,N,N′,N′-tetraacetic acid (EGTA), 3 mM non-aqueous magnesium chloride (MgCl2), 60 mM K-lactobionate, 20 mM taurine, 10 mM monopotassium phosphate (KH₂PO4), 20 mM 4-(2-hydroxyethyl)piperazine-1-ethanesulfonic acid (HEPES), 110 mM D-sucrose, and 1 g/L of bovine serum albumin (BSA). All chemicals for MiR05 were obtained from Sigma-Aldrich. For the detection of HepG2 cell mitochondrial respiration, the reagents and inhibitors used for the modified SUIT-036 protocol [63 ] included malic acid, palmitoyl carnitine, cytochrome C, pyruvic acid, succinic acid, adenosine diphosphate, glutamic acid, carbonyl cyanide 3-chlorophenylhydrazone (CCCP), rotenone, and antimycin A. Except for adenosine diphosphate, obtained from Merck (Darmstadt, Germany), all chemicals were purchased from Sigma-Aldrich (St. Louis, MO, USA).