Pretreatment and Enzymatic Hydrolysis of Sorghum Bran

Sorghum bran has potential to serve as a low‐cost feedstock for production of fuel ethanol. Sorghum bran from a decortication process (10%) was used for this study. The approximate chemical composition of sorghum bran was 30% starch, 18% hemicellulose, 11% cellulose, 11% protein, 10% crude fat, and 3% ash. The objective of this research was to evaluate the effectiveness of selected pretreatment methods such as hot water, starch degradation, dilute acid hydrolysis, and combination of those methods on enzymatic hydrolysis of sorghum bran. Methods for pretreatment and enzymatic hydrolysis of sorghum bran involved hot water treatment (10% solid, w/v) at 130°C for 20 min, acid hydrolysis (H₂SO₄), starch degradation, and enzymatic hydrolysis (60 hr, 50°C, 0.9%, v/v) with commercial cellulase and hemicellulose enzymes. Total sugar yield by using enzymatic hydrolysis alone was 9%, obtained from 60 hr of enzyme hydrolysis. Hot water treatment facilitated and increased access of the enzymes to hemicellulose and cellulose, improving total sugar yield up to 34%. Using a combination of starch degradation, optimum hot water treatment, and optimum enzymatic hydrolysis resulted in maximum total sugar yield of up to 75%.     

High‐Starch and High‐β‐Glucan Barley Fractions Milled with Experimental Mills

This study focused on the performance of two hulless barley cultivars (Doyce and Merlin) and one commercial husked (hulled) sample using experimental milling. The purpose was to use experimental milling as a preliminary indicator of the milled streams with potential use for fuel ethanol production and fractions that could be used in food products. Experimental mills designed for flour production evaluation from wheat were Chopin CD1 Auto, Quadrumat Sr, Buhler, and an experimental Ross roller mill walking flow. Results indicate that the shorts had the highest levels of β‐glucan from all the mills. However, the β‐glucan content in the break flours was highest with the roller mill walking flow and the Chopin CD1 for the hulless cultivars. The lowest β‐glucan content in the break flour was found with the Buhler for Doyce. Break flour and, to a slightly lesser extent, reduction flour from all cultivars tested on all mills contained the highest starch content (up to 83%) and are therefore most appropriate for use as feedstock for fuel ethanol production. Conversely, bran and shorts from all cultivars and mills were lowest in starch (as low as 25%), making them ideal as low‐starch food ingredients.     

Activity‐Guided Fractionation to Identify Blue Wheat (UC66049 Triticum aestivum L.) Constituents Capable of Inhibiting In Vitro Starch Digestion

The inhibition or delay of starch digestion by dietary compounds could help manage postprandial blood glucose levels. The objective of this study was to identify constituents from whole grain blue wheat capable of decreasing α‐amylase‐catalyzed starch digestion. An activity‐guided fractionation approach based on liquid chromatography was used to identify solvent‐ and alkaline‐extractable blue wheat constituents reducing α‐amylase‐mediated starch digestion in vitro. Fatty acids, potentially released from cell wall polymers by alkaline hydrolysis, inhibited the digestion of amylose, probably through the formation of amylose‐lipid complexes. However, the degradation of amylopectin was not affected by fatty acids. In addition, 1‐(3,5‐dihydroxyphenyl)heneicosan‐2‐one, a 5‐(2′‐oxoalkyl)resorcinol, was found to reduce starch digestion. However, because the digestion of both amylopectin and amylose was reduced, the inhibition mechanism was different from that of fatty acids. Further research is needed to evaluate whether this component also reduces starch digestion in vivo. Other phenolic compounds of blue wheat such as anthocyanins or hydroxycinnamates were not identified as major starch digestion inhibitors by using the activity‐guided fractionation approach.     

Protein engineering of Sulfolobus solfataricus maltooligosyltrehalose synthase to alter its selectivity

Maltooligosyltrehalose synthase (MTSase) is one of the key enzymes involved in trehalose production from starch and catalyzes an intramolecular transglycosylation reaction by converting the alpha-1,4- to alpha,alpha-1,1-glucosidic linkage. Mutations at residues F206, F207, and F405 were constructed to change the selectivity of the enzyme because the changes in selectivity could reduce the side hydrolysis reaction of releasing glucose and thus increase trehalose production from starch. As compared with wild-type MTSase, F405Y and F405M MTSases had decreased ratios of the initial rate of glucose formation to that of trehalose formation in starch digestion at 75 degrees C when wild-type and mutant MTSases were, respectively, used with isoamylase and maltooligosyltrehalose trehalohydrolase (MTHase). The highest trehalose yield from starch digestion was by the mutant MTSase having the lowest initial rate of glucose formation to trehalose formation, and this predicted high trehalose yield better than the ratio of catalytic efficiency for hydrolysis to that for transglycosylation.     

Methods for Characterization of Residual Starch in Distiller's Dried Grains with Solubles (DDGS)

The objective of this study was to establish methods for determining the content and components of residual starch in distiller's dried grains with solubles (DDGS), a coproduct from dry‐grind corn ethanol production. Four DDGS prepared in our laboratory and one DDGS obtained from a commercial ethanol manufacturer were used for the study. Quantitative analysis of total residual sugar (TRS) in DDGS was performed by determining d ‐glucose produced by enzymatic hydrolysis of oligosaccharides and residual starch remaining in hexane‐defatted DDGS after being dispersed in 90% DMSO. The TRS consisted of free glucose, oligosaccharides, and residual starch. The commercial manufacturer's DDGS contained more TRS (15.8%, w/w db) than the laboratory‐processed DDGS (2.4–2.9%, w/w db). The content of residual starch remaining in the commercial DDGS (5.5% w/w db) was also larger than the laboratory‐processed DDGS (1.9–2.5% w/w db). Analyses of molecular weight distribution showed that the residual starch in DDGS consisted of short‐chain amylose and amylopectin, respectively, as the major and minor components. The short‐chain amylose molecules constituted 86.5–94.1% of the residual starch. The major population of the short‐chain amyloses had an average degree of polymerization (DP) of 85, closely resembling the length of enzyme‐resistant fragments of amylose‐lipid complexes.     

Logistic模型模拟乙醇发酵产物动力学

乙醇发酵产物动力学的研究有助于更好的认识发酵过程,为其工业放大及生产操作条件的优化提供理论基础。基于Logistic方程的菌体生长动力学模型可较好的描述细胞生长期及细胞自身抑制作用,但由于该模型方程中的比例参数与积分常数没有明显的生物学意义,使其应用受到了限制。该文从生物学与化学工程学结合角度对Logistic模型方程重新参数化,将发酵产物乙醇生成动力学与酵母生长动力学方程类比,给出了乙醇浓度的显式函数模型,模型中不再出现酵母菌浓度变量,大大简化了模型,并且赋予参数其物理意义;在研究了以葡萄糖和玉米淀粉为原料乙醇质量浓度、总糖质量浓度在不同底物质量浓度和料液比条件下随发酵时间的变化规律的基础上运用该模型拟合了以葡萄糖和玉米淀粉为原料进行乙醇发酵的试验数据,结果表明:模型值与试验数据具有较好一致性,拟合度均大于0.97,可见该重新参数化的Logistic模型可以描述发酵生产乙醇过程中产物乙醇的动力学行为,具有预测工业上实际发酵过程中乙醇浓度的潜力。     

木薯燃料乙醇生产的技术提升及全生命周期能耗分析

发展燃料乙醇是中国替代能源战略大框架下的成熟模式,木薯燃料乙醇因为不耗用粮食原料也日益提上发展日程.该文引入生命周期理论,对木薯燃料乙醇系统的三个阶段进行了能耗分析,重点讨论了燃料生产阶段采用新旧工艺对周期能耗的影响.能耗计算发现,采用新工艺可以较大地增加系统周期的净能量产出,提高系统的能效;加强副产品的开发,使用农家肥替代化肥也可产生同样的效果.     

Effects of chemical modification on in vitro rate and extent of food starch digestion: an attempt to discover a slowly digested starch.

Differences in glycemic and insulinemic responses to dietary starch are directly related to the rate of starch digestion. Chemical modification of starch may allow for the production of a slowly digested starch that could be used for the treatment of certain medical modalities. An in vitro method was utilized to evaluate the effects of chemical modification on the rate and extent of raw and cooked starch digestion. The extent of starch digestion was significantly reduced by dextrinization, etherification, and oxidation. However, the rate of starch digestion was not significantly affected by chemical modification. For most modified starches, as the degree of modification increased, the extent of digestion decreased, suggesting an increase in the amount of resistant starch. The results of this study suggest that chemically modified starch has a metabolizable energy value of <16.7 kJ/g. Chemically modified starch ingredients may serve as a good source of resistant starch in human and animal diets.     

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.     

中国生物质燃料乙醇项目能量生产效率评估

为了对玉米和木薯乙醇的能量和可再生能量生产效率进行评估,该文统计了玉米和木薯乙醇生命周期能耗,并用市场价值量法按照主副产品的能耗进行了分配。计算出玉米和木薯燃料乙醇的净能量和净可再生能量。并计算了单产和化肥用量变化时的净能量和净可再生能量的变化。计算结果显示,玉米、木薯乙醇的净能量分别为1.472 MJ/L和2.417 MJ/L,净可再生能量分别为1.474 MJ/L和2.459 MJ/L。使用玉米、木薯生产燃料乙醇在能量生产和再生能量生产上都是可行的,木薯乙醇比玉米乙醇可行性更高,单产和化肥用量是提高能源利用和再生能源的关键因素,加强副产品的开发和使用有机肥代替化肥有利于提高系统的能效,提高系统的可再生性。     

Kinetics of the surface hydrolysis of raw starch by glucoamylase

The hydrolysis of raw starch catalyzed by glucoamylase has been studied with starch granules of different sizes by use of an amperometric glucose sensor by which the direct and continuous observation of the concentration of glucose can be achieved even in a thick raw starch suspension. The initial rate of the enzymatic hydrolysis in the raw starch suspension increased with increasing concentration of the enzyme to approach a saturation value and was proportional to the amount of substrate. Also, the rate was proportional to the specific surface area of the substrate. The experimental results can be explained well by the rate equations derived from a three-step mechanism, which consists of adsorption of the free enzyme onto the surface of the substrate, reaction of the adsorbed enzyme with the substrate, and liberation of the product.     

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.     

Biocatalysis for the production of industrial products and functional foods from rice and other agricultural produce

Many industrial products and functional foods can be obtained from cheap and renewable raw agricultural materials. For example, starch can be converted to bioethanol as biofuel to reduce the current demand for petroleum or fossil fuel energy. On the other hand, starch can also be converted to useful functional ingredients, such as high fructose and high maltose syrups, wine, glucose, and trehalose. The conversion process involves fermentation by microorganisms and use of biocatalysts such as hydrolases of the amylase superfamily. Amylases catalyze the process of liquefaction and saccharification of starch. It is possible to perform complete hydrolysis of starch by using the fusion product of both linear and debranching thermostable enzymes. This will result in saving energy otherwise needed for cooling before the next enzyme can act on the substrate, if a sequential process is utilized. Recombinant enzyme technology, protein engineering, and enzyme immobilization are powerful tools available to enhance the activity of enzymes, lower the cost of enzyme through large scale production in a heterologous host, increase their thermostability, improve pH stability, enhance their productivity, and hence making it competitive with the chemical processes involved in starch hydrolysis and conversions. This review emphasizes the potential of using biocatalysis for the production of useful industrial products and functional foods from cheap agricultural produce and transgenic plants. Rice was selected as a typical example to illustrate many applications of biocatalysis in converting low-value agricultural produce to high-value commercial food and industrial products. The greatest advantages of using enzymes for food processing and for industrial production of biobased products are their environmental friendliness and consumer acceptance as being a natural process.     

Mechanism and enzymatic contribution to in vitro test method of digestion for maize starches differing in amylose content

To determine the rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) contents in a starch sample, the addition of amyloglucosidase is often used to convert hydrolyzates from α-amylase digestion to glucose. The objectives of this study were to investigate the exact role of amyloglucosidase in determining the digestibility of starch and to understand the mechanism of enzymatic actions on starch granules. Four maize starches differing in amylose content were examined: waxy maize (0.5% amylose), normal maize (≈27% amylose), and two high-amylose starches (≈57 and ≈71% amylose). Notably, without amyloglucosidase addition, the RS content increased from 4.3 to 74.3% for waxy maize starch, 29.7 to 76.5% for normal maize starch, 65.8 to 88.0% for starch with 57% amylose, and 68.2 to 90.4% for the starch with 71% amylose. In the method without α-amylase addition, less RS was produced than without added amyloglucosidase, except in maize at 71% amylose content. Scanning electron microscopy (SEM) revealed the digestive patterns of pinholes with α-amylase and burrowing with amyloglucosidase as well as the degree of digestion between samples. To understand the roles of amyloglucosidase and α-amylase in the in vitro test, multiple analytical techniques including gel permeation chromatography, SEM, synchrotron wide-angle X-ray diffraction, and small-angle X-ray scattering were used to determine the molecular and crystalline structure before and after digestion. Amyloglucosidase has a significant impact on the SDS and RS contents of granular maize starches.     

Chemical composition of distillers grains, a review

In recent years, increasing demand for ethanol as a fuel additive and decreasing dependency on fossil fuels have resulted in a dramatic increase in the amount of grains used for ethanol production. Dry-grind is the major process, resulting in distillers dried grains with solubles (DDGS) as a major coproduct. Like fuel ethanol, DDGS has quickly become a global commodity. However, high compositional variation has been the main problem hindering its use as a feed ingredient. This review provides updated information on the chemical composition of distillers grains in terms of nutrient levels, changes during dry-grind processing, and causes for large variation. The occurrence in grain feedstock and the fate of mycotoxins during processing are also covered. During processing, starch is converted to glucose and then to ethanol and carbon dioxide. Most other components are relatively unchanged but concentrated in DDGS about 3-fold over the original feedstock. Mycotoxins, if present in the original feedstock, are also concentrated. Higher fold of increases in S, Na, and Ca are mostly due to exogenous addition during processing, whereas unusual changes in inorganic phosphorus (P) and phytate P indicate phytate hydrolysis by yeast phytase. Fermentation causes major changes, but other processing steps are also responsible. The causes for varying DDGS composition are multiple, including differences in feedstock species and composition, process methods and parameters, the amount of condensed solubles added to distiller wet grains, the effect of fermentation yeast, and analytical methodology. Most of them can be attributed to the complexity of the dry-grind process itself. It is hoped that information provided in this review will improve the understanding of the dry-grind process and aid in the development of strategies to control the compositional variation in DDGS.     

Importance of Location of Digestion and Colonic Fermentation of Starch Related to Its Quality

For decades, quality of starch‐based foods has been associated with the in vivo measured glycemic index or the in vitro digestion rate‐based categories of rapidly digestible, slowly digestible, and resistant starch (RS). Glycemic index has been related to health‐based endpoints mostly through correlative or observational studies, with mechanisms proposed but not well established. Here, we bring forth the concept of locational delivery of glucose from dietary starches to the distal small intestine to elicit an ileal brake effect, as well as short‐chain fatty acid production from RS fermentation to cause a colonic brake. Both effects slow gastric emptying and, in turn, extend nutrient (i.e., energy) delivery to the body and may decrease appetite and promote weight management. Slowly digestible starches are currently a popular topic of research, although where they are digested and the released glucose is delivered in the small intestine is not known. A proposal is to further study and establish this mechanism of appetite and food intake regulation so that starch‐based ingredients and foods can be developed that promote both the ileal and colonic brake mechanisms.     

广西木薯燃料乙醇项目能效评估

广西具有丰富的木薯资源,以木薯为原料生产的燃料乙醇是一种可再生的燃料。采用净能量和净可再生能量两个指标评估木薯燃料乙醇系统的能量和可再生能量生产的效率,并对木薯乙醇在生命周期内与外界环境的能量交换进行了统计,把能量消耗按照燃料和其副产品进行了分配;以及按照是否再生进行了分别统计。计算结果表明,使用木薯生产燃料乙醇在能量生产和再生能量生产上是可行的,木薯乙醇的净能量为2．417MJ／L,净可再生能量是2．458MJ／L;广西的木薯资源每年能净产出相当于3．508万t汽油的可再生燃料。木薯单产和化肥用量是提高能源利用和再生能源的关键因素;加强副产品的开发有利于提高系统的能效,使用可再生的有机肥代替化肥,能有效的提高系统的可再生性。     

生物质资源能源化与高值利用研究现状及发展前景

生物质是唯一能够直接转化为燃料的可再生能源,其开发利用既可以弥补低碳能源的需求,减少环境污染,也是中国实现"碳中和"目标的重要手段。该研究围绕以秸秆为主的生物质资源制备清洁能源和高值利用的总目标,系统分析生物质资源通过生物或热化学等转化途径制备气、液、固三相清洁能源的综合利用技术和模式,重点论述厌氧消化制备生物燃气、水热催化炼制醇烃燃料、裂解液化与生物油提质和生物质制备固体燃料4项技术发展现状与研究进展。在4项生物质转化技术中,厌氧消化制备生物天然气工业化程度最高,由于其大都基于大型养殖场建立,可有效解决原料收集问题,而且厌氧消化技术与沼气净化技术相对较为成熟,生物天然气可直接作为燃料、电力和热力来源供用户使用;由于生物质制备液体燃料中存在转化过程成本较高、产物分离困难、提质效率低、产品不稳定等问题,很难与当前应用端平稳接轨,因此水热催化炼制醇烃燃料、裂解液化制备生物油技术规模化发展水平较低;对于生物质制备固体燃料,其成型技术较为成熟,配套炉具的研发也有效解决了成型燃料应用端的问题,其规模化应用最大的难点在于原料的收集与存储。文章最后对未来生物天然气、生物质液体燃料与固体成型燃料发展前景进行展望,为实现农村生物质资源高效制备清洁能源及高值利用提供借鉴。     

Extraction of β‐Glucan from Oat Bran in Laboratory Scale

Effects of various enzymes and extraction conditions on yield and molecular weight of β‐glucans extracted from two batches of commercial oat bran produced in Sweden are reported. Hot‐water extraction with a thermostable α‐amylase resulted in an extraction yield of ≈76% of the β‐glucans, while the high peak molecular weight was maintained (1.6 × 10⁶). A subsequent protein hydrolysis significantly reduced the peak molecular weight of β‐glucans (by pancreatin to 908 × 10³ and by papain to 56 × 10³). These results suggest that the protein hydrolyzing enzymes may not be pure enough for purifying β‐glucans. The isolation scheme consisted of removal of lipids with ethanol extraction, enzymatic digestion of starch with α‐amylase, enzymatic digestion of protein using protease, centrifugation to remove insoluble material, removal of low molecular weight components using dialysis, precipitation of β‐glucans with ethanol, and air‐drying.     

一株降解生木薯淀粉的曲霉菌株的筛选、鉴定及其淀粉降解特性

本研究利用以生木薯淀粉为唯一碳源的筛选培养基,从腐烂木薯渣中分离筛选出一株可以降解生木薯淀粉的真菌菌株RSDF-7。根据RSDF-7形态和18SrDNA与28SrDNA之间的内转录间隔区（internal transcribed spacer,ITS）序列分析的结果,初步认定该菌株为曲霉属。菌株RSDF-7的粗酶液对多种不同的生淀粉底物均有水解效果;在以大米和玉米淀粉为底物时,其生淀粉分解活力比较高,分别为42%和40%。菌株RSDF-7的粗酶液具有良好的低pH稳定性,对生木薯淀粉的最适作用温度为50℃,最适作用pH为4.5。在30min的吸附后,RSDF-7的粗酶液对生木薯淀粉的吸附力高达60%。使用HPLC对粗酶液的酶解产物进行检测,结果发现酶解产物中仅存在葡萄糖,表明菌株RSDF-7所产的生淀粉降解酶主要为糖化酶。扫描电镜观察结果发现,经RSDF-7粗酶液酶解后的生木薯粉颗粒破裂,形成空洞,说明RSDF-7粗酶液对生淀粉有较强的水解作用。可以预见,经纯化后的曲霉菌株RSDF-7生淀粉酶将来可以用于基于酶解的木薯淀粉转化。