Dl lactic acid

ChCl (ref C7527)
and dl-malic
acid (ref 240176) from Sigma-Aldrich (China), malonic acid (ref A11526)
from Alfa Aesar (Kandel, Germany), and dl-lactic acid (ref
125065000) from Acros Organics were used for the DES preparation.
Systems were prepared by heating the mixture of the two components
to 80 °C, in the case of ChCl/malonic acid and ChCl/lactic acid,
and 90 °C in the case of ChCl/malic acid, under constant stirring,
until a clear liquid was formed. The mixtures were then allowed to
cool to room temperature before being used in characterization or
extraction experiments.

Ethanol (absolute) was obtained from Alkaloid (Skopje, Macedonia). 1,2-propanediol (p.a., >99%) was purchased from Valerus (Sofia, Bulgaria); galangin (≥95%), choline chloride (≥98%) and Nile Red from Sigma Aldrich (Switzerland); methanol (HPLC grade, ≥99.8%), D/L-lactic acid (≥88%), D (−) fructose (≥99%) and betaine (98%) from Fisher Chemical (Loughborough, UK); D/L-malic acid (>99%) from Acros Organics (Geel, Belgium); Folin-Ciocalteau reagent, dry pyridine and N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) from Merck (Darmstadt, Germany); aluminium chloride anhydrous from Fluka (Buchs, Switzerland) and pinocembrin (≥95%) from Extrasynthese (Genay, France). The chemicals 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide (MTT, #M2128-1G), L-glutamine (#G7513) and Dulbecco's phosphate buffered saline (PBS, #D8537) were purchased from Merck (Sigma-Aldrich, Steinheim, Germany). HCOOH originated from Chimspektar OOD, Bulgaria. The media, sera, enzymes and antibiotics for culturing of the cell lines were delivered from Capricorn®, Germany: MEM (#MEM-A), DMEM (#DMEM-HPA), horse serum (#HOS-1A), fetal bovine serum (#FBS-HI-12A), CM-1 (#800125), Trypsin (#TRY-1B10, # TRY-2B10), Accutase® (#ACC-1B), and Pen/Strep 100 × (#PS-B).

In this experiment, L. plantarum WiKim18, which was previously isolated from kimchi [11 (link)], was cultured at 30 °C for 16 h in de Man, Rogosa, and Sharpe (MRS) media (Miller, Becton Dickinson, and Co., Sparks, MD, USA). The bacterial culture was harvested by centrifugation at 5000×g for 20 min and diluted in MRS medium at an absorbance of 0.05 at 600 nm. To monitor the growth effect in the different pH environments, MRS medium was prepared with the addition of dl-lactic acid (Fisher Scientific, Loughborough, UK), HCl (Daegjung, Gyeonggi-do, Korea), acetic acid (Fluka, Buchs, Switzerland), malic acid (Daegjung, Gyeonggi-do, Korea), d-lactic acid (TCI, Shanghai, China), and l-lactic acid (Sigma-Aldrich, St. Louis, USA). The effect of various organic acids on the growth of L. plantarum was measured at 600 nm using a microplate reader (Tecan, Mannedorf, Zurich, Switzerland).
The bacteria were cultivated in MRS media. The pH was adjusted by adding HCl (18.0 mM; pH 5.5, 34.0 mM; pH 5.0 and 55.0 mM; pH 4.5), dl-Lactic acid (24.2 mM; pH 5.5, 48.4 mM; pH 5.0 and 84.6 mM; pH 4.5), acetic acid (1.4 mM; pH 5.5, 3.6 mM; pH 5.0 and 10.4 mM; pH 4.5), malic acid (11.0 mM; pH 5.5, 27.0 mM; pH 5.0 and 52.9 mM; pH 4.5), d-lactic acid (25.4 mM; pH 5.5, 53.1 mM; pH 5.0 and 100.2 mM; pH 4.5) and l-lactic acid (20.9 mM; pH 5.5, 43.0 mM; pH 5.0 and 80.9 mM; pH 4.5).