Spectronic 21d uv visible spectrophotometer

According to Miguel [44 (link)], the methanolic extracts from the five halophytes aerial parts were tested for antioxidant activity by scavenging 2,2-diphenyl-1-picrylhydrazyl (DPPH•) (Sigma-Aldrich, Darmstadt, Germany). Methanol was employed to prepare various concentrations of methanolic extract (5, 10, 20, 30, 40, and 50 mg mL⁻¹). This concentration range was estimated using either a higher or lower concentration in a preliminary test. A reaction mixture comprising equal volumes of newly generated 0.3 mM DPPH• and each concentration of the methanolic extract was prepared, forcefully mixed, and maintained in the dark for 30 min at 25 °C. Additionally, a parallel positive control was performed and treated similarly to the treatments, using ascorbic acid as the standard antioxidant at doses of 1.0, 2.5, 5, 10, 15, and 20 mg mL⁻¹. A spectrophotometer (Milton Roy Spectronic 21D UV-Visible Spectrophotometer, Ivyland, PA, USA) was used to measure the absorbance after incubation at 517 nm. The quantity of methanolic extract necessary to decrease DPPH’s absorbance by 50% (SC₅₀) was visually estimated.

Clostridium thermocellum DSM 1313 was grown in MTC medium containing 1.1 g/L cellobiose. Cultures were inoculated into hungate tubes containing 10 mL of medium and initial headspace of 10 % CO₂ (v/v), 5 % H₂ (v/v), and the balance N₂. Methyl viologen was added to medium which was then pre-warmed overnight prior to inoculation. H₂O₂ was added to pre-warmed medium immediately prior to inoculation. Cultures were inoculated with 1 mL of overnight grown culture and growth was monitored using a Milton Roy Spectronic 21D UV–Visible Spectrophotometer (Milton Roy Company). Soluble fermentation products were measured using HPLC (see HPLC analysis portion of methods) and headspace H₂ % was measured using an Agilent 6850 GC equipped with a thermal conductivity detector (TCD) for CO₂ and H₂ quantification (Agilent Technologies, USA).
In preliminary batch fermentations, the end of fermentation was determined based on a decrease in culture OD₆₀₀, common in C. thermocellum batch fermentations and thought to correspond with the onset of stationary phase. Samples for end-product determinations were collected immediately after the final OD600 reading was taken. End-products were normalized to the average maximum OD600 achieved during batch fermentation.