Poly(ε-L-lysine) and poly(L-diaminopropionic acid) co-produced from spent mushroom substrate fermentation: potential use as food preservatives

Poly(ε-L-lysine) and poly(L-diaminopropionic acid) are valuable homopoly (amino acids) with antimicrobial properties and mainly produced in submerged fermentation. In this study, we investigated their co-production using waste biomass and spent mushroom substrate in solid-state fermentation. Simultaneous production of poly(L-diaminopropionic acid) and poly(ε-L-lysine) was achieved in a single fermentation process using pearl oyster mushroom residues as substrate, with the supplement of glycerol and corn steep liquor. After optimization of the fermentation parameters, the maximum yield of poly(ε-L-lysine) and poly(L-diaminopropionic acid) reached 51.4 mg/g substrate and 25.4 mg/g substrate, respectively. The optimal fermentation conditions were 70% initial moisture content, pH of 6.5, 30°C and an inoculum size of 14%. Furthermore, the fermentation time was reduced from 8 days to 6 days using repeated-batch solid-state fermentation. Finally, the antimicrobial effects of poly(L-diaminopropionic acid) and poly(ε-L-lysine) were evaluated in freshly pressed grape juice, which indicated tremendous potential of this mixture in its use as biological preservative.

聚ε-赖氨酸（Poly(ε-L-lysine)）与聚L-二氨基丙酸（poly(L-diaminopropionic acid)）是两类具备抗菌活性的高价值均聚氨基酸（homopoly(amino acids)），传统生产方式以深层发酵（submerged fermentation）为主。本研究探索了以废弃生物质与菇渣（spent mushroom substrate）为基质的固态发酵（solid-state fermentation）工艺，实现了二者的共生产。以珍珠菇菌渣作为发酵底物，辅以甘油（glycerol）与玉米浆（corn steep liquor），成功在单批次发酵流程中同步合成了聚L-二氨基丙酸与聚ε-赖氨酸。经发酵参数优化后，聚ε-赖氨酸与聚L-二氨基丙酸的最高产量分别达到51.4 mg/g底物与25.4 mg/g底物，最优发酵条件为：初始含水率70%、pH值6.5、发酵温度30℃、接种量14%。采用重复分批固态发酵（repeated-batch solid-state fermentation）工艺后，发酵周期从8天缩短至6天。最后，本研究在鲜榨葡萄汁中对聚L-二氨基丙酸与聚ε-赖氨酸的抗菌效果进行了评价，结果表明该混合产物作为生物保鲜剂拥有巨大的应用潜力。