酚酮类对树干毕赤酵母乙醇发酵及脂肪酸组成的影响

Effect of phenolic ketones on ethanol fermentation and cellular lipid composition of Pichia stipitis

摘要:

木质素降解产物对微生物产生的抑制作用，是燃料乙醇生物炼制的主要瓶颈之一。本文以树干毕赤酵母为发酵菌株，研究木质素降解产物中3种酚酮类 (4-羟基苯乙酮、4-羟基-3-甲氧基苯乙酮、4-羟基-3,5-二甲氧基苯乙酮) 对其木糖乙醇发酵及酵母细胞脂肪酸组成的影响。采用高效液相色谱 (HPLC) 和气相色谱-质谱联用 (GC/MS) 技术对乙醇发酵性能和酵母细胞脂肪酸组成进行分析。研究结果表明，酚酮类物质对乙醇发酵呈现抑制作用且其分子量越低抑制作用越明显，当4-羟基苯乙酮浓度为1.50 g/L时，发酵24 h的木糖利用率、乙醇得率和乙醇浓度分别下降了42.47%、5.30%和9.76 g/L；培养基中存在酚酮类物质时，酵母细胞中的不饱和脂肪酸的比例上升，添加1.50 g/L的3种酚酮类物质后，树干毕赤酵母细胞不饱和脂肪酸和饱和脂肪酸的比例从原来的2.58分别上升到3.03、3.06和3.61，酵母细胞膜的流动性随之上升，不稳定性提高。因此，酚酮类物质能够降低酵母生长、提高不饱和脂肪酸的比例以及降低乙醇发酵能力，有效降低或去除木质素降解产物含量是提高木质纤维原料生物炼制的关键。

Abstract:

Lignin degradation products are toxic to microorganisms, which is one of the bottlenecks for fuel ethanol production. We studied the effects of phenolic ketones (4-hydroxyacetophenone, 4-hydroxy-3-methoxy-acetophenone and 4-hydroxy-3,5-dimethoxy-acetophenone) derived from lignin degradation on ethanol fermentation of xylose and cellular lipid composition of Pichia stipitis NLP31. Ethanol and the cellular fatty acid of yeast were analyzed by high performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry (GC/MS). Results indicate that phenolic ketones negatively affected ethanol fermentation of yeast and the lower molecular weight phenolic ketone compound was more toxic. When the concentration of 4-hydroxyacetophenone was 1.5 g/L, at fermentation of 24 h, the xylose utilization ratio, ethanol yield and ethanol concentration decreased by 42.47%, 5.30% and 9.76 g/L, respectively, compared to the control. When phenolic ketones were in the medium, the ratio of unsaturated fatty acids to saturated fatty acids (UFA/SFA) of yeast cells was improved. When 1.5 g/L of three aforementioned phenolic ketones was added to the fermentation medium, the UFA/SFA ratio of yeast cells increased to 3.03, 3.06 and 3.61, respectively, compared to 2.58 of the control, which increased cell membrane fluidity and instability. Therefore, phenolic ketones can reduce the yeast growth, increase the UFA/SFA ratio of yeast and lower ethanol productivity. Effectively reduce or remove the content of lignin degradation products is the key to improve lignocellulose biorefinery.