Fig. 4

Betanin production in yeast strains expressing UGTs from B. vulgaris. A Betanin titer (mg/L) measured as extracellular and intracellular content after 48 h of cultivation in MM (pABA⁻) media supplemented with 20 g/L glucose. The color of culture supernatant is also shown for the strains. B Normalized UV–visible spectra of the extracted cultures. Betanin at maximum absorbance of 534 nm is present in strains with integrated UGT73A36, UGT73A39, and DbB5GT. C Mass spectrometry analysis of betacyanins. The presence of isobetanin (retention time at 4.54 min) and betanin (retention time 3.85 min) in beetroot extract standard sample is shown in mass spectra (left). The spectra of the yeast cultures (right) confirm the synthesis of betanin (and not isobetanin) in strains with integrated UGT73A36, UGT73A39, and DbB5GT