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Bioprocess for hydrolysis of galacto-oligosaccharides in soy molasses and tofu whey by recombinant Pseudomonas chlororaphis

Solaiman Daniel, Daniel K.Y. Solaiman, Richard D. Ashby, Nicole V. Crocker
Biocatalysis and agricultural biotechnology 2020 v.24 pp. 101529
Pseudomonas chlororaphis, alpha-galactosidase, biopolymers, bioprocessing, biosurfactants, byproducts, chromosomes, culture media, fermentation, galactooligosaccharides, gene expression, genes, genetic engineering, hydrolysis, molasses, plasmid vectors, raffinose, secretion, stachyose, tofu, wastes, whey
The main objective of the study was to develop a bioprocess to hydrolyse galacto-oligosaccharides (GOs) using genetically engineered Pseudomonas chlororaphis which could produce biopolymers and biosurfactants. To this end, alpha-galactosidase genes were expressed in P. chlororaphis transformants either via a plasmid vector (i.e., strain [dAG]) or integrated into the chromosome (i.e., strain [chr::AG]). Pseudomonas secretion signals for protein were tested to facilitate extracellular secretion of the gene product. Furthermore, a two-stage condensed-cell-density fermentation process was adopted to enable hydrolysis of GOs by the P. chlororaphis recombinants. The results showed that the recombinant P. chlororaphis strains could hydrolyse GOs in culture media containing raffinose alone, stachyose alone, crude soy molasses, and tofu whey waste byproducts. Specifically, the most active recombinant P. chlororaphis [dAG] strain reduced the levels of raffinose (0.5% w/v) to <0.1% (w/v) and stachyose (0.21% w/v) to 0.15% (w/v) in E* medium after 7-d incubation. When used in E* medium containing soy molasses (SM), [dAG] strain reduced raffinose (0.1% w/v) and stachyose (0.56% w/v) to 0.03% w/v and 0.25% w/v, respectively, after a 7-d incubation. In E* medium containing tofu whey (TW), [dAG] reduced raffinose (0.11% w/v) and stachyose (0.27% w/v) to 0.05% w/v and 0.08% w/v, respectively, after an 8-d incubation. The other recombinant P. chlororaphis strain [chr::AG] was also capable of reducing GO levels in supplemented E* media but at a lower reactivity than the [dAG] strain (see detail in text).