Production of 2-keto-gluconic acid from glucose by immobilized Pseudomonas plecoglossicida resting cells.

2-Keto-d-gluconic acid (2KGA) is an important organic acid derived from d-glucose and is used to produce the food antioxidant erythorbic acid. To improve the 2KGA production performance and cell reusability, various carriers such as calcium alginate, k-carrageenan, chitosan, and poly(vinyl alcohol)-alginate were evaluated to immobilize Pseudomonas plecoglossicida JUIM01 resting cells. Calcium alginate was shown to be a suitable carrier since the immobilized cells had the highest number of reuse times and produced the highest 2KGA concentration of 171.77 g/L, with a productivity of 3.58 g/L·h and conversion ratio of 98.38%. The cell concentration, cultivation temperature, aeration rate and initial glucose concentration were further optimized in a 5-L airlift bioreactor to obtain the best 2KGA production performance by calcium alginate-immobilized P. plecoglossicida cells. Under the optimal conditions including a cell concentration of 4.0 g/L, glucose concentration of 126.0 g/L, temperature of 34 °C and aeration rate of 2.8 L/min, 134.45 g/L 2KGA was produced by alginate-immobilized P. plecoglossicida cells within 30 h, with a total productivity of 4.48 g/L·h and yield of 1.07 g/g (conversion ratio of over 99.0%). The immobilized cells maintained a stable conversion capacity after nine reuses and 25 days of storage at 4 °C, which indicated that calcium alginate immobilization of P. plecoglossicida cells had industrial practicability for 2KGA production.