An innovative strategy of recycling miscellaneous waste carbohydrates from high-fructose syrup production for Pichia pastoris fermentation

Recycling waste carbon source for fermentation is of great interests and high practical value. However, the process suffered some problems like unclear carbohydrate composition, low nutrition content, presence of various contaminants and high cost for pretreatment. Currently, the high-fructose syrup (HFS) production industry in China generates a large amount of waste liquid containing miscellaneous waste carbohydrates (MWC), which has a notable environmental impact. To recycle MWC for Pichia pastoris fermentation, the composition of MWC was analyzed and the fermentation processes were optimized. The composition of MWC was determined as 802.3 g L−1 total carbohydrate, 480 g L−1 glucose, 92 g L−1 fructose, 103.6 g L−1 maltose, 36.8 g L−1 maltotriose and 89.9 g L−1 other oligosaccharides with different degrees of polymerization (DPs 4–16). After the fermentation medium and conditions for pGAP/pAOX1-P. pastoris were optimized, MWC were employed as the alternative carbon source to culture the two strains to produce endo-β-1,3-glucanase in 7-L bioreactors. Using MWC for pGAP-P. pastoris culture, the dry cell weight (DCW) and endo-β-1,3-glucanase activity reached 69.1 g L−1 and 171.8 U mL−1, respectively, which were the same levels as in the batch using glucose as the carbon source. When using MWC and the self-designed DO-Stat-Time feeding strategy for pAOX1-P. pastoris culture, the maximum DCW and enzyme activity reached 83.6 g L−1 and 212.3 U mL−1, which improved 41.4% and 34.9%, respectively compared with the control group. This study established cleaner production procedures for both HFS and P. pastoris fermentation industries by considerably reducing environmental pollution and decreasing the production cost.