Potassium nitrate

Two concentrations of lactose and potassium nitrate were tested for a pool of strains in preliminary tests.
lactose fermentation was tested in a modified API 50CH medium containing the following: lactose 5 or 20 g.L⁻¹ (Panreac, Lyon, France), tryptone 10 g.L⁻¹, yeast extract 5 g.L⁻¹, K₂HPO₄, 0.25 g.L⁻¹, MnSO₄ 0.05 g.L⁻¹, and bromocresol purple 0.17 g.L⁻¹. The medium was inoculated using 1% (v/v) of 48-h cultures in YEL, and incubated at 30 °C under anaerobiosis (using the Anaerocult A system, Merck, Darmstadt, Germany). The production of acid from lactose was determined from the colour change of bromocresol purple from purple to yellow after 2, 5, and 7 days of incubation.
Nitrate reductase activity was detected by means of the Griess reagent (Biomérieux, Marcy l'Etoile, France) after incubation of cultures at 30 °C under microaerophilic conditions (air atmosphere without agitation) in a broth containing potassium nitrate, 0.5 or 1.5 g.L⁻¹ (VWR International, Fontenay-sous-Bois, France), tryptone (Biokar Diagnostics, Allone, France) 10 g.L⁻¹, yeast extract (Biokar Diagnostics) 5 g.L⁻¹, and glucose (Grosseron, Saint-Herblain, France) 1 g.L⁻¹, according to Dalmasso et al. (2011 (link)). The results of the tests were read after 2 and 5 days of incubation.
All the tests were carried out in triplicate.

RIT (melting temperature of 124.97 °C and degradation temperature of 160 °C [33 (link),34 (link)]) was supplied by AbbVie Deutschland GmbH & Co. KG (Ludwigshafen, Germany). The copolymer PVPVA (Kollidon^® VA64) with a weight-average molar mass of 65,000 g/mol was obtained from BASF SE (Ludwigshafen, Germany). Silica gel was purchased from BINDER GmbH (Tuttlingen, Germany). Sodium nitrate (purity ≥ 99%) was purchased from Merck KGaA (Darmstadt, Germany), and potassium nitrate (purity ≥ 99%) was purchased from VWR International GmbH (Darmstadt, Germany). All substances were used without further purification. Water was purified using a Milli-Q^® Advantage A10 purification system of Merck KGaA (Darmstadt, Germany).

RIT was obtained from AbbVie Deutschland GmbH & Co. KG (Ludwigshafen, Germany). The copolymer PVPVA (Kollidon^®® VA64) with a weight-average molar mass of 65,000 g/mol was purchased from BASF SE (Ludwigshafen, Germany). Hydrochloric acid (10%) was purchased from AppliChem GmbH (Darmstadt, Germany), and potassium acetate (purity ≥ 99%) was purchased from Carl Roth GmbH & Co. KG (Karlsruhe, Germany). Acetone (purity ≥ 99.8%), sodium dihydrogen phosphate (purity ≥ 99%), and disodium hydrogen phosphate dihydrate (purity ≥ 99.5%) were purchased from Merck KGaA (Darmstadt, Germany). Magnesium nitrate hexahydrate (purity ≥ 98%), potassium nitrate (purity ≥ 99%), and potassium sulfate (purity ≥ 99%) were purchased from VWR International GmbH (Darmstadt, Germany). All substances were used without further purification. Water was freshly prepared with a Milli-Q^®® Advantage A10 purification system from Merck KGaA (Darmstadt, Germany).