Lactic acid

Lactic acid (88 w%) was purchased from Carl Roth (Austria), ethanol of two purity levels (96% and 99.9%) was purchased from Australco (Austria). The cation-exchange resins Amberlyst 15, Amberlyst 46 and Amberlyst 48 (Dow, Germany) were used as acid catalysts.

Hexamethylenetetramine (≥99%), lactic acid (≥98%) and aluminum chloride (98%) were obtained from Carl Roth Gmbh & Co Kg (Karlsruhe, Germany). 2,2-diphenyl-1-picrylhydrazyl (DPPH) (99%), chlorogenic acid (≥95%), ferulic acid (≥99%), salicylic acid (≥99%), methanol (≥99.9%), hesperidin (≥90%), benzoic acid (≥97%), myricetin (≥96%), rutin (95%), naringenin (≥95%), coumarin (≥99%), caffeic acid (≥98%), vanillic acid (≥97%), gallic acid (≥98%), ellagic acid (≥97%), and syringic acid (≥97%), of analytical grade were obtained from Sigma-Aldrich Corp (Taufkirchen, Germany). Folin-Ciocalteu reagent, trifluoracetic acid (99%) and acetonitrile (≥99.8%) were supplied by Merck KGAA (Darmstadt, Germany). MRS with Tween 80 broth was obtained from Biolife Italiana S. r. l. (Milan, Italy). Coumaric acid and luteolin were obtained from: Chromadex, Inc. (Los Angeles, CA, USA). Sodium carbonate and acetic acid (99.9%) were bought from Reachem S.r. o. (Bratislava, Slovakia). Bidistilled water was prepared by means of distillation apparatus Thermo Fisher Scientific, Inc. (Fremont, CA, USA).