温度对固定化酵母酒精分批发酵的影响及动力学模型

该文以甜高粱茎秆汁液为原料,探讨了温度（25～37 ℃）对甜高粱汁固定化酵母酒精分批发酵的影响,并对不同温度下固定化酵母乙醇发酵的动力学模型进行了研究。结果表明：温度的升高可以提高细胞生长速率,但过高的温度却阻碍了细胞的生长,从而影响了酒精的产量。应用Hinshelwood模型,分别对酒精发酵过程中细胞生长动力学和酒精合成动力学进行了模拟,得到25～34℃范围内不同温度下各种动力学参数。在此基础上,进一步研究了温度同细胞生长动力学参数之间的内在联系,得到酒精分批发酵过程中酵母细胞质量浓度的变化同温度以及底物质量浓度之间的一般关系式,验证试验结果表明,该模型具有很好的适用性。     

以羽毛、人发为枯草芽胞杆菌KD-N2液体发酵碳、氮源生产角蛋白酶模型的建立

以枯草芽胞杆菌(Bacillus subtilis)KD-N2为发酵菌种,分别以羽毛、人发为碳、氮源,研究了5 L发酵罐内角蛋白酶的发酵动力学。根据Logistic方程和Luedeking-Piret方程建立了菌体生长和产物生成动力学模型。根据实验数据确定了模型参数,以羽毛为唯一碳、氮源发酵过程中菌体生长动力学模型为dX/dt =0.1013(1－X/0.3742)X,角蛋白酶生成动力学模型为dP/dt =276.69dX/dt －3.6X,以人发为碳、氮源底物发酵过程中菌体生长动力学模型为dX/dt =0.0728(1－X/0.197)X,角蛋白酶生成动力学模型为dP/dt =422.34dX/dt + 5.187X。     

产细菌素的嗜酸乳杆菌WS发酵动力学模型的建立(简报)

为了嗜酸乳杆菌进一步工业化生产,需要确定嗜酸乳杆菌的发酵动力学模型,该文将嗜酸乳杆菌WS接种到MRS培养基进行发酵培养,根据其发酵过程特点,在Logistic方程和Luedeking-Pitet方程的基础上,建立了嗜酸乳杆菌WS发酵过程中菌体生长、基质消耗和产物形成的动力学模型,并用实际发酵实验值进行验证.结果表明,模型预测值和实验值吻合较好,说明该文建立的模型能较好地预测实际的发酵过程.     

CO一步法C. autoethanogenum发酵产乙醇的工艺研究

合成气/CO发酵制备燃料乙醇是一项具有吸引力的新技术,为促进C.autoethanogenum在该技术中的应用,对C.autoethanogenum的乙醇发酵工艺及过程参数进行了研究。结果表明,C.autoethanogenum代谢木糖的产物以乙酸为主,只产生少量乙醇;与无机氮源相比较,C.autoethanogenum在含有机氮源的培养基中生长迅速,菌体浓度高。在3 L发酵罐中进行C.autoethanogenum的批式发酵试验,采用木糖生长-CO发酵两步法,乙醇主要在CO发酵阶段产生,最高乙醇质量浓度为1.71 g/L;发酵罐经改进之后,采用CO一步法发酵,虽然得到的菌体浓度降低了,但是发酵时间延长,最高乙醇质量浓度达到7.36 g/L,而乙酸质量浓度在整个发酵过程中均低于1.1 g/L。此外,研究发现发酵液的pH值和氧化还原电位ORP与乙酸/乙醇产物分布密切相关,尤其是pH值。上述研究结果可为C.autoethanogenum发酵CO生产乙醇的中试放大提供参考。     

分枝杆菌降解植物甾醇制备雄烯二酮转化过程研究

在分批发酵中研究了分枝杆菌（Mycobacterium sp-UV-8）的菌体生长、基质消耗及产物生成的特征,基于Logistic方程和Leudeking-piret方程建立了描述分批发酵过程的动力学模型及模型参数,并对实验数据与模型进行了验证比较,平均相对误差均小于7 ％,模型计算值与试验数据拟合良好,基本反映了Mycobacterium sp-UV-8分批发酵过程的动力学特征,表现出很好的适用性,为产业化设计和生产提供了可靠的保障。     

弹性蛋白酶分批发酵动力学模型的建立

对70L发酵罐内Bacillus sp.EL31410分批发酵动力学模型进行了研究。在Logistic方程和Luedeking-Piret方程的基x础上,建立了弹性蛋白酶分批发酵动力学模型。根据实验数据确定了模型参数,得到菌体生长动力学模型为dx/dt=0.180(1-x/9.77)x,弹性蛋白酶生产动力学模型为dp/dt=-dx/dt=4.278x以及葡萄糖消耗动力学模型-ds/dt=0.03(dx/dt)-7.53x。将模型预测值与实验值进行比较,结果表明模型具有良好的适用性。     

棉籽粕固态发酵过程及其动力学模型构建

为了研究枯草芽孢杆菌Bs-1在工业化条件下发酵棉籽粕的过程,该文采用槽式发酵方式,测定了发酵过程中物料堆温、含水率、粗蛋白、酸溶性蛋白和游离棉酚质量分数;并采用Logistic方程建立芽孢杆菌Bs-1生长模型,在其与粗蛋白、酸溶性蛋白和游离棉酚质量分数相关性分析的基础上,构建了固态发酵动力学模型并进行了发酵成本分析。结果表明:棉籽粕槽式发酵过程中的温度和含水率均呈现一定的变化规律;粗蛋白质量分数、酸溶性蛋白质量分数分别较发酵前提高了9.28%和46.51%,游离棉酚质量分数降低了42.31%。Bs-1的生长与粗蛋白质量分数(R2=0.831)和酸溶性蛋白质量分数(R2=0.867)呈正相关,与游离棉酚质量分数(R2=0.976)呈负相关;建立了棉籽粕固态发酵动力学模型。分析表明,该模型计算值与试验值能较好吻合,且发酵成本低。表明该模型可应用于工业化生产,对实现发酵棉籽粕的产业化生产,具有较好的参考价值。     

机械活化玉米淀粉的微生物降解性能

为了提高玉米淀粉的微生物降解反应活性,采用搅拌球磨机对玉米淀粉进行机械活化,以活化时间为60 min的玉米淀粉和原淀粉为原料,酒曲为降解试剂进行微生物降解反应,并以降解产物的葡萄糖值（Dextrose Equivalent,DE）为评价指标,分别研究了糊化温度、pH值、淀粉浓度、降解时间、降解温度、酒曲培养液用量等因素对降解产物中葡萄糖值的影响,并采用扫描电镜对淀粉降解过程中的颗粒进行形貌观察。结果表明,机械活化预处理能提高玉米淀粉微生物降解反应液中葡萄糖的含量,且活化淀粉未经糊化就能直接被微生物降解,降解60 min时的DE值为36.76%,与原淀粉相比,提高了27.80个百分点。说明机械活化作用破坏玉米淀粉紧密的颗粒表面和结晶结构,有效地提高了微生物降解反应活性。     

甜高粱茎汁及茎渣同步糖化发酵工艺优化

为了提高甜高粱秸秆乙醇生产中茎汁和茎渣的利用,以甜高粱茎汁及其渣为发酵原料,对茎汁茎渣混合原料同步糖化乙醇发酵的工艺条件进行优化研究。采用Plackett-Burman(PB)筛选设计试验筛选出影响甜高粱茎秆渣汁同步糖化乙醇发酵的显著因素。采用响应面法建立了同步糖化发酵乙醇生产的乙醇产量数学模型。根据该模型进行了工艺参数的优化,以乙醇产量为指标,试验所得甜高粱茎秆渣汁同步糖化化乙醇发酵的优化工艺条件为:发酵温度36.58℃,混合纤维素酶添加量=23.5(FBU/m L)/35.25(CBU/m L),甜高粱渣汁质量体积比为8.2%,理论预测乙醇产量为89.2%,在此条件下进行验证试验,乙醇产量为88.98%,平均质量浓度,验证了数学模型的有效性,为提高甜高粱茎汁及茎渣混合原料同步糖化发酵产乙醇和提高发酵效率提供参考。     

耐高温东方伊萨酵母乙醇发酵特性

燃料乙醇作为一种可再生清洁能源,越来越受到人们的广泛关注,选育出一株耐高温乙醇发酵菌株对于提高乙醇发酵效率、降低能耗和生产成本具有重要意义。该文对分离自烟叶腐解物中的耐高温乙醇发酵菌株HN-1进行生理生化特性试验及分子生物学鉴定,并对其发酵特性进行初步研究。结果表明:HN-1菌株为东方伊萨酵母,能够利用葡萄糖和果糖发酵生产乙醇,但不能利用木糖、半乳糖等。该菌株的最适生长温度为38℃,乙醇发酵的合适温度范围为38~45℃,且随着发酵温度的升高,乙醇生成速率加快,发酵时间缩短。38℃乙醇发酵的最适葡萄糖浓度为120 g/L,乙醇产量为58.19 g/L,乙醇产率为0.460 g/g。利用玉米秸秆水解液发酵,乙醇产量为20.74 g/L,乙醇产率为0.468 g/g,达到葡萄糖理论转化率的91.6%。该研究为生物乙醇的高温发酵提供了宝贵的菌种资源和技术支撑。     

Effect of Harvest Moisture Content on Selected Yellow Dent Corn: Dry‐Grind Fermentation Characteristics and DDGS Composition

Efficiently utilizing the nongrain portion of the corn plant as ruminant food and the grain for ethanol will allow the optimization of both food and fuel production. Corn and corn stover could be more effectively used if they were harvested earlier before dry down. Corn harvested at different moisture contents (MCs) may exhibit different processing characteristics for the ethanol industry, because of differences in physical and chemical properties. Therefore, the objective of this study was to investigate the effect of corn harvest MC on dry‐grind fermentation characteristics and dried distillers grains with solubles (DDGS) composition. Pioneer hybrid 32D78 was harvested at seven different dates from August 21 to November 23, 2009, with harvest MCs ranging from 73 to 21% (wb). The corn samples with different harvest MCs were evaluated by a conventional dry‐grind process. Final ethanol concentration from the corn with harvest MC of 54% (kernel dent stage) was 17.9% (v/v), which was significantly higher (0.5–1.2 percentage points) than the mature corn with lower harvest MCs (P < 0.05). Ethanol conversion efficiencies for the corn with harvest MCs of 73 and 54% (wb) were 98.5 and 93.2%, respectively, whereas ethanol conversion efficiencies for the corn with lower harvest MCs were significantly lower (P < 0.05), ranging between 83.2 and 88.3%. For DDGS composition, with corn harvest MC decreasing from 73 to 21% (wb), the residual starch concentration increased from 7.7 to 15.2%, the crude protein concentration decreased from 29.4 to 24.9%, and the neutral detergent fiber concentration decreased from 26.6 to 20.6%.     

Comparison of Enzymatic (E‐Mill) and Conventional Dry‐Grind Corn Processes Using a Granular Starch Hydrolyzing Enzyme

A new low temperature liquefaction and saccharification enzyme STARGEN 001 (Genencor International, Palo Alto, CA) with high granular starch hydrolyzing activity was used in enzymatic dry‐grind corn process to improve recovery of germ and pericarp fiber before fermentation. Enzymatic dry‐grind corn process was compared with conventional dry‐grind corn process using STARGEN 001 with same process parameters of dry solid content, pH, temperature, enzyme and yeast usage, and time. Sugar, ethanol, glycerol and organic acid profiles, fermentation rate, ethanol and coproducts yields were investigated. Final ethanol concentration of enzymatic dry‐grind corn process was 15.5 ± 0.2% (v/v), which was 9.2% higher than conventional process. Fermentation rate was also higher for enzymatic dry‐grind corn process. Ethanol yields of enzymatic and conventional dry‐grind corn processes were 0.395 ± 0.006 and 0.417 ± 0.002 L/kg (2.65 ± 0.04 and 2.80 ± 0.01 gal/bu), respectively. Three additional coproducts, germ 8.0 ± 0.4% (db), pericarp fiber 7.7 ± 0.4% (db), and endosperm fiber 5.2 ± 0.6% (db) were produced in addition to DDGS with enzymatic dry‐grind corn process. DDGS generated from enzymatic dry‐grind corn process was 66% less than conventional process.     

Ethanol Production from Pearl Millet Using Saccharomyces cerevisiae

Four pearl millet genotypes were tested for their potential as raw material for fuel ethanol production in this study. Ethanol fermentation was performed both in flasks on a rotary shaker and in a 5‐L bioreactor using Saccharomyces cerevisiae (ATCC 24860). For rotary‐shaker fermentation, the final ethanol yields were 8.7–16.8% (v/v) at dry mass concentrations of 20–35%, and the ethanol fermentation efficiencies were 90.0–95.6%. Ethanol fermentation efficiency at 30% dry mass on a 5‐L bioreactor reached 94.2%, which was greater than that from fermentation in the rotary shaker (92.9%). Results showed that the fermentation efficiencies of pearl millets, on a starch basis, were comparable to those of corn and grain sorghum. Because pearl millets have greater protein and lipid contents, distillers dried grains with solubles (DDGS) from pearl millets also had greater protein content and energy levels than did DDGS from corn and grain sorghum. Therefore, pearl millets could be a potential feedstock for fuel ethanol production in areas too dry to grow corn and grain sorghum.     

Hydrolysis and Fermentation of Pericarp and Endosperm Fibers Recovered from Enzymatic Corn Dry‐Grind Process

A modified dry‐grind corn process has been developed that allows recovery of both pericarp and endosperm fibers as coproducts at the front end of the process before fermentation. The modified process is called enzymatic milling (E‐Mill) dry‐grind process. In a conventional dry‐grind corn process, only the starch component of the corn kernel is converted into ethanol. Additional ethanol can be produced from corn if the fiber component can also be converted into ethanol. In this study, pericarp and endosperm fibers recovered in the E‐Mill dry‐grind process were evaluated as a potential ethanol feedstock. Both fractions were tested for fermentability and potential ethanol yield. Total ethanol yield recovered from corn by fermenting starch, pericarp, and endosperm fibers was also determined. Results show that endosperm fiber produced 20.5% more ethanol than pericarp fiber on a g/100 g of fiber basis. Total ethanol yield obtained by fermenting starch and both fiber fractions was 0.370 L/kg compared with ethanol yield of 0.334 L/kg obtained by fermenting starch alone.     

Effects of Different Mill Types on Ethanol Production Using Uncooked Dry‐Grind Fermentation and Characteristics of Residual Starch in Distiller's Dried Grains (DDG)

This study aimed to investigate impacts of milling methods on ethanol production using an uncooked dry‐grind (cold fermentation) process and characterize residual starch in the distiller's dried grains (DDG) coproduct. Four corn lines with different chemical compositions were ground with cyclone, ultra‐centrifugal, or hammer mills equipped with a screen of 0.5 mm opening and used for the cold fermentation process. Greater starch hydrolysis and ethanol yield were obtained from cyclone‐milled corn, resulting from larger damaged starch contents and smaller particle sizes of the ground corn. Corn grains and ground corn after five‐month storage showed less starch hydrolysis than the freshly ground counterpart. Residual starch (2.8–8.0%) with large proportions of intact amylopectin contents (up to 42.5%) was found in the DDG from all types of milling. The results suggested that the entrapment of starch granules in ground corn and a low activity of amylolytic enzymes at a high ethanol concentration were accountable for the remaining of starch in the DDG.     

Pericarp Fiber Separation from Corn Flour Using Sieving and Air Classification

In the dry‐grind process, starch in ground corn (flour) is converted to ethanol, and the remaining corn components (protein, fat, fiber, and ash) form a coproduct called distillers dried grains with solubles (DDGS). Fiber separation from corn flour would produce fiber as an additional coproduct that could be used as combustion fuel, cattle feed, and as feedstock for producing valuable products such as “cellulosic” ethanol, corn fiber gum, oligosaccharides, phytosterols, and polyols. Fiber is not fermented in the dry‐grind corn process. Its separation before fermentation would increase ethanol productivity in the fermenter. Recently, we showed that the elusieve process, a combination of sieving and elutriation (air flow), was effective in fiber separation from DDGS. In this study, we evaluated the elusieve process for separating pericarp fiber from corn flour. Corn flour remaining after fiber separation was termed “enhanced corn flour”. Of the total weight of corn flour, 3.8% was obtained as fiber and 96.2% was obtained as enhanced corn flour. Neutral detergent fiber (NDF) of corn flour, fiber, and enhanced corn flour (dry basis) were 9.0, 61.5, and 5.7%, respectively. Starch content of corn flour, fiber, and enhanced corn flour (dry basis) were 68.8, 23.5, and 71.3%, respectively. Final ethanol concentration from enhanced corn flour (14.12% v/v) was marginally higher than corn flour (13.72% v/v). No difference in ethanol yields from corn flour and enhanced corn flour was observed. The combination of sieving and air classification can be used to separate pericarp fiber from corn flour. The economics of fiber separation from corn flour using the elusieve process would be governed by the production of valuable products from fiber and the revenues generated from the valuable products.     

Improvement of Dry‐Fractionation Ethanol Fermentation by Partial Germ Supplementation

Ethanol fermentation of dry‐fractionated grits (corn endosperm pieces) containing different levels of germ was studied with the dry‐grind process. Partial removal of the germ fraction allows for marketing the germ fraction and potentially more efficient fermentation. Grits obtained from a dry‐milling plant were mixed with different amounts of germ (2, 5, 7, and 10% germ of the total sample) and compared with control grits (0% germ). Fermentation rates of germ‐supplemented grits (2, 5, 7, and 10% germ) were faster than control grits (0% germ). Addition of 2% germ was sufficient to achieve a high ethanol concentration (19.06% v/v) compared with control grits (18.18% v/v). Fermentation of dry‐fractionated grits (92, 95, and 97% grits) obtained from a commercial facility was also compared with ground whole corn (control). Fermentation rates were slower and final ethanol concentrations were lower for commercial grits than the control sample. However, in a final experiment, commercial grits were subjected to raw starch hydrolyzing (RSH) enzyme, resulting in higher ethanol concentrations (20.22, 19.90, and 19.49% v/v for 92, 95, and 97% grits, respectively) compared with the whole corn control (18.64% v/v). Therefore, high ethanol concentrations can be achieved with dry‐fractionated grits provided the inclusion of a certain amount of germ and the use of RSH enzyme for controlled starch hydrolysis.     

Dry‐Grind Processing of Corn with Endogenous Liquefaction Enzymes

An amylase corn has been developed that produces an α‐amylase enzyme that is activated in the presence of water at elevated temperatures (>70°C). Amylase corn in the dry‐grind process was evaluated and compared with the performance of exogenous amylases used in dry‐grind processing. Amylase corn (1–10% by weight) was added to dent corn (of the same genetic background as the amylase corn) as treatments and resulting samples were evaluated for dry‐grind ethanol fermentation using 150‐g and 3‐kg laboratory procedures. Ethanol concentrations during fermentation were compared with the control treatment (0% amylase corn addition or 100% dent corn) which was processed with a conventional amount of exogenous α‐amylase enzymes used in the dry‐grind corn process. The 1% amylase corn treatment (adding 1% amylase corn to dent corn) was sufficient to liquefy starch into dextrins. Following fermentation, ethanol concentrations from the 1% amylase corn treatment were similar to that of the control. Peak and breakdown viscosities of liquefied slurries for all amylase corn treatments were significantly higher than the control treatment. In contrast, final viscosities of liquefied slurries for all amylase corn treatments were lower than those of the control. Protein, fat, ash, and crude fiber contents of DDGS samples from the 3% amylase corn treatment and control were similar.     

预发酵方式对餐厨垃圾酸化抑菌及甲烷发酵的影响

餐厨垃圾水分和有机物含量高,在收集储运过程中易酸腐变臭,影响其资源化利用。该文在新鲜餐厨垃圾中分别接种酵母菌和乙酸菌进行乙醇和乙酸预发酵,预发酵后的餐厨垃圾与酒糟混合进行甲烷发酵,并与不接任何菌种的对照组比较,考察2种预发酵方式对餐厨垃圾酸化抑菌及其与酒糟混合甲烷发酵的影响。研究结果表明,乙酸和乙醇预发酵对餐厨垃圾均具有良好的酸化抑菌效果,其大肠杆菌和金黄葡萄球菌数均比对照组降低了2个数量级以上;累积甲烷产量由高到低的顺序是:乙醇预发酵对照乙酸预发酵组,前者累积产甲烷量比对照组和乙酸预发酵组分别提高21.3%和49.8%;乙醇预发酵组乙醇浓度最高,而乙酸和丙酸浓度均最低;相反,乙酸预发酵组挥发性脂肪酸浓度积累导致产甲烷菌活性较低,其产气效率最低。因此,乙醇预发酵是一种既能实现餐厨垃圾酸化抑菌,又能维持发酵系统的稳定性,提高其后续产甲烷效率的有效预发酵方式。     

Protease Treatment to Improve Ethanol Fermentation in Modified Dry Grind Corn Processes

To improve fractionation efficiency in modified dry grind corn processes, we evaluated the effectiveness of protease treatment in reducing residual starch in endosperm fiber. Three schemes of protease treatment were conducted in three processes: 1) enzymatic milling or E‐Mill, 2) dry fractionation with raw starch fermentation or dry RS, and 3) dry fractionation with conventional fermentation or dry conv. Kinetics of free amino nitrogen production were similar in both dry and wet fractionation (E‐Mill), indicating that proteolysis was effective in all three schemes. At the end of fermentation, endosperm fiber was recovered and its residual starch measured. Using protease treatment, residual starch in the endosperm fiber was reduced by 1.9% w/w (22% relative reduction) in dry conv and 1.7% w/w (8% relative reduction) in dry RS, while no reduction was observed in the E‐Mill process. Protease treatment increased ethanol production rates early in fermentation (≤24 hr) but final ethanol concentrations were unaffected in both dry RS and E‐Mill. In dry conv, the addition of protease resulted in a decline in final ethanol concentration by 0.3% v/v, as well as a higher variability in liquefaction product concentration (higher standard deviations in the glucose and maltose yields). Protease treatment can be used effectively to enhance modified dry grind processes.