Background: Xanthan gum is an industrialized polysaccharide produced by Xanthomonas genus. Alternative carbon sources for Xanthomonas culturing may help reducing its production cost. Nejayote, a residue from maize nixtamalization process, is an alternative culture medium substrate to produce xanthan. In this study, industrial and semi-industrial nejayote alone or in combination with supplements, were tested for xanthan production by Xantomonas campestris (1 × 108 cells/mL inoculum), using YGC medium as control, in 100 mL and 1 L volumes. Cellular growth was determined by the colorimetric MTT reduction assay (OD 540 ). Xanthan pyruvate and acetyl groups from nejayote plus supplement cultures in the bioreactor were evaluated (OD 570).
Results: Industrial nejayote steadily produced up to 4 g/L xanthan, as compared with YGC medium control, which increased its production over time up to 9.3 g/L at 96 h. Cellular activity assay revealed that the highest values after 24 h (3.88 and 2.71 OD 540 for YGC and industrial nejayote, respectively). Nejayote supplemented with MgSO4 •7 H2O resulted in the highest xanthan production (10.8 g/L), but low cell growth (3.6 and 1.82 OD 540 for YGC and nejayote plus supplement, respectively), after 96 h of culture. Furthermore, gum yield reached up to 6 g/L and 1.9 OD 540, after 96 h of nejayote plus supplement culture, using a 14 L bioreactor. Xanthan pyruvate and acetyl groups from nejayote plus supplement cultures in the bioreactor resulted in similar amounts (0.107 and 0.130 OD 570 , respectively), compared with a commercial biopolymer (0.148 and 0.127 OD 570 respectively).
Conclusions: X. campestris effectively grew and produced industrial-quality xanthan gum in nejayote substrate-containing culture medium, thus providing an inexpensive alternative for bioremediation.