Ethane-1,2-diol, glycerol, 1,2-propanediol, 1,2-butanediol, 1,2-hexanediol, acetaldehyde, propionaldehyde, butyraldehyde, pentanaldehyde, hexanaldehyde, ethanol, 1,3-propanediol, 1-propanol, 1-butanol, 1-pentanol, 1-hexanol, acetic acid, 3-hydroxypropionic acid, propionic acid, butyric acid, pentanoic acid and hexanoic acid were measured via HPLC (Jasco, Tokyo, Japan). For HPLC, an Aminex HPX-87H chromatographic column was used with an upstream pre-column (Biorad, Richmond, CA, USA) and a refractive index detector (Perkin Elmer, Series 200a, Waltham, Massachusetts, USA) and an intelligent autosampler (Jasco, Tokyo, Japan). Temperature of the column was maintained at 65°C by a column oven (Shimadzu, Tokyo, Japan). Samples from the bioreactor were diluted with MilliQ water and mixed with 20% v/v sulfuric acid and injected into 0.5 mM sulfuric acid mobile phase.
For quantification of 3-HPA, the modified photometric method according to Circle et al. [34 ], with acrolein as standard was used. Briefly, 200 μL of the sample (diluted to fit in the range of the assay) was mixed with 150 μL of DL-tryprophan, followed by addition of 600 μL of hydrochloric acid (37%), and incubating the mixture for 20 min at 37°C. The resulting purple colour was measured spectrophotometrically at 560 nm and the absorbance was compared with the standard curve.
For quantification of 3-HPA, the modified photometric method according to Circle et al. [34 ], with acrolein as standard was used. Briefly, 200 μL of the sample (diluted to fit in the range of the assay) was mixed with 150 μL of DL-tryprophan, followed by addition of 600 μL of hydrochloric acid (37%), and incubating the mixture for 20 min at 37°C. The resulting purple colour was measured spectrophotometrically at 560 nm and the absorbance was compared with the standard curve.