Posgrado de Ingeniería Química, Universidad Michoacana de San Nicolás de Hidalgo, Francisco J. Múgica S/N, Ciudad Universitaria, 58030, Morelia, Mich, México.
Facultad de Ingeniería Química, Universidad Michoacana de San Nicolás de Hidalgo, Francisco J. Múgica S/N, Ciudad Universitaria, 58030, Morelia, Mich, México.
Microb Cell Fact. 2023 Jun 29;22(1):119. doi: 10.1186/s12934-023-02110-5.
A processing methodology of raw starch extraction from avocado seeds (ASs) and a sequential hydrolysis and fermentation bioprocess in just a few steps was successfully obtained for the bioethanol production by a single yeast Saccharomyces cerevisiae strain and this research was also to investigate the optimum conditions for the pretreatment of biomass and technical procedures for the production of bioethanol. It successfully resulted in high yields and productivity of all the experiments from the laboratory scale and the pilot plant. Ethanol yields from pretreated starch are comparable with those in commercial industries that use molasses and hydrolyzed starch as raw materials.
Before the pilot-scale bioethanol production, studies of starch extraction and dilute sulfuric acid-based pretreatment was carefully conducted. The amount of starch extracted from dry and fresh avocado seed was 16.85 g ± 0.34 g and 29.79 ± 3.18 g of dry starch, representing a yield of ∼17% and 30%, respectively. After a dilute sulfuric acid pretreatment of starch, the released reducing sugars (RRS) were obtained and the hydrolysate slurries containing glucose (109.79 ± 1.14 g/L), xylose (0.99 ± 0.06 g/L), and arabinose (0.38 ± 0.01 g/L). The efficiency of total sugar conversion was 73.40%, with a productivity of 9.26 g/L/h. The ethanol fermentation in a 125 mL flask fermenter showed that Saccharomyces cerevisiae (Fali, active dry yeast) produced the maximum ethanol concentration, p at 49.05 g/L (6.22% v/v) with a yield coefficient, Y of 0.44 gg, a productivity or production rate, r at 2.01 g/L/h and an efficiency, Ef of 85.37%. The pilot scale experiments of the ethanol fermentation using the 40-L fermenter were also successfully achieved with essentially good results. The values of pY, r, and Ef of the 40-L scale were at 50.94 g/L (6.46% v/v), 0.45 gg, 2.11 g/L/h, and 88.74%, respectively. Because of using raw starch, major by-products, i.e., acetic acid in the two scales were very low, in ranges of 0.88-2.45 g/L, and lactic acid was not produced, which are less than those values in the industries.
The sequential hydrolysis and fermentation process of two scales for ethanol production using the combination of hydrolysis by utilizing dilute sulfuric acid-based pretreatment and fermentation by a single yeast Saccharomyces cerevisiae strain is practicable and feasible for realistic and effective scale-up strategies of bioethanol production from the starch of avocado seeds.
从鳄梨种子（ASs）中提取生淀粉的加工方法以及在几个步骤中进行的顺序水解和发酵生物工艺已成功获得，用于由单一酵母酿酒酵母菌株生产生物乙醇，并且该研究还旨在研究生物质预处理的最佳条件和生产生物乙醇的技术程序。它成功地从实验室规模和中试工厂获得了所有实验的高产量和生产力。预处理淀粉的乙醇产率可与使用糖蜜和水解淀粉作为原料的商业行业相媲美。
在进行中试规模的生物乙醇生产之前，仔细研究了淀粉提取和稀硫酸预处理。从干鳄梨种子和鲜鳄梨种子中提取的淀粉量分别为 16.85 g ± 0.34 g 和 29.79 g ± 3.18 g 的干淀粉，分别代表约 17%和 30%的产率。稀硫酸预处理淀粉后，得到释放的还原糖（RRS），并且水解物浆液含有葡萄糖（109.79 g ± 1.14 g/L）、木糖（0.99 g ± 0.06 g/L）和阿拉伯糖（0.38 g ± 0.01 g/L）。总糖转化率效率为 73.40%，生产力为 9.26 g/L/h。在 125 mL 摇瓶发酵罐中的乙醇发酵表明，酿酒酵母（Fali，活性干酵母）产生的最大乙醇浓度为 49.05 g/L（6.22%v/v），产率系数 Y 为 0.44 gg，生产率或生产速率 r 为 2.01 g/L/h，效率 Ef 为 85.37%。使用 40-L 发酵罐的中试规模乙醇发酵实验也成功完成，结果基本良好。40-L 规模的 pY、r 和 Ef 值分别为 50.94 g/L（6.46%v/v）、0.45 gg、2.11 g/L/h 和 88.74%。由于使用生淀粉，两个规模的主要副产物，即两种规模的乙酸非常低，范围为 0.88-2.45 g/L，并且不产生乳酸，这些值均小于工业值。
利用稀硫酸预处理进行水解和利用单一酵母酿酒酵母菌株进行发酵相结合的两个规模的顺序水解和发酵工艺用于从鳄梨种子淀粉生产乙醇是可行的，适用于生物乙醇生产的现实有效的放大策略。
