Co‐production of galactonic acid and lactobionic acid from cheese whey using recyclable engineered <i>Pseudomonas putida</i>

Whey is a main by‐product generated during cheese manufacture. It contains abundant lactose and proteins and is a valued raw material in many countries. Pseudomonas putida KT2440 is a promising microbial strain for biobased chemical production. In our previous studies, this strain was confirmed owning high ability to oxidise galactose. Besides, we have constructed a recombinant strain P. putida KT2440 (pBB‐GDH1) harbouring a novel glucose dehydrogenase that capable of oxidising lactose. Based on these, the potential of this engineered P. putida in whey utilisation deserves further exploration. This research aimed to establish a bioprocess to convert whey lactose into galactonic acid and lactobionic acid using engineered P. putida . Lactose in cheese whey powder was hydrolysed by Bacillus coagulans β‐galactosidase into glucose and galactose. P. putida KT2440 (pBB‐GDH1) was inoculated into the whey powder hydrolysate and galactose was converted into galactonic acid. Then, the bacterial cells were recovered and employed for lactobionic acid production from fresh whey powder solution. Three independent experiments were performed, and the mean value were taken as the results. Pseudomonas putida KT2440 (pBB‐GDH1) exhibited a higher lactose‐oxidising activity compared with the wild‐type strain. It could utilise glucose and proteins in cheese whey powder hydrolysate for growth and convert galactose to galactonic acid. 25.45 g/L galactonic acid was obtained with a productivity of 1.06 g/L/h. The recovered cells maintained excellent lactose oxidation ability. After optimisation of biocatalytic reactions, 301.58 g/L lactobionic acid was obtained from cheese whey powder containing 300 g/L lactose in a 3 L bioreactor. The lactobionic acid productivity reached 2.28 g/L/h with a yield of 96.67%. This study established a sustainable and economic aldonic acids co‐production strategy from cheese whey powder.