Saccharification of explosively dried corn

Very rapid or explosive drying of grains such as corn leads to obvious physical changes in the macrostructure of the grain kernel, probable alteration in starch molecular structure, and reduction in starch average molecular weight. These changes lead to greater susceptibility to attack by liquefying and saccharifying enzymes. Rates of formation of nonreducing and reducing sugars by liquefying and saccharifying enzymes applied to explosively dried and milled yellow dent corn and small-kernel flint corn were 3.3-10.6 times greater than rates for the normally milled grains. The enzymatic conversion of explosively dried flint corn containing absorbed ethyl alcohol, as would be the case if it had been used as an adsorbent to dewater aqueous ethyl alcohol, was not significantly different from that of ethyl-alcohol-free flint corn.     

Biological pretreatment of corn stover with Phlebia brevispora NRRL‐13108 for enhanced enzymatic hydrolysis and efficient ethanol production

Biological pretreatment of lignocellulosic biomass by white‐rot fungus can represent a low‐cost and eco‐friendly alternative to harsh physical, chemical, or physico‐chemical pretreatment methods to facilitate enzymatic hydrolysis. In this work, solid‐state cultivation of corn stover with Phlebia brevispora NRRL‐13018 was optimized with respect to duration, moisture content and inoculum size. Changes in composition of pretreated corn stover and its susceptibility to enzymatic hydrolysis were analyzed. About 84% moisture and 42 days incubation at 28°C were found to be optimal for pretreatment with respect to enzymatic saccharification. Inoculum size had little effect compared to moisture level. Ergosterol data shows continued growth of the fungus studied up to 57 days. No furfural and hydroxymethyl furfural were produced. The total sugar yield was 442 ± 5 mg/g of pretreated corn stover. About 36 ± 0.6 g ethanol was produced from 150 g pretreated stover per L by fed‐batch simultaneous saccharification and fermentation (SSF) using mixed sugar utilizing ethanologenic recombinant Eschericia coli FBR5 strain. The ethanol yields were 32.0 ± 0.2 and 38.0 ± 0.2 g from 200 g pretreated corn stover per L by fed‐batch SSF using Saccharomyces cerevisiae D5A and xylose utilizing recombinant S. cerevisiae YRH400 strain, respectively. This research demonstrates that P. brevispora NRRL‐13018 has potential to be used for biological pretreatment of lignocellulosic biomass. This is the first report on the production of ethanol from P. brevispora pretreated corn stover. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:365–374, 2017     

双酶法水解辐照改性马铃薯淀粉动力学研究

为了解辐照改性马铃薯淀粉的酶解特性,用α-淀粉酶和糖化酶同时作用于马铃薯原淀粉和经400 kGy剂量辐照处理后淀粉,考察了pH值、酶解温度、α-淀粉酶用量、糖化酶用量对反应速率的影响.以米氏方程为基础,用Lineweaver-Burk法求解动力学参数.结果表明,辐照后马铃薯淀粉的酶解反应速率明显高于马铃薯原淀粉.在单一水解体系中,α-淀粉酶和糖化酶对辐照前后马铃薯淀粉的降解都遵循Michaelis-Menten方程,α-淀粉酶的Km分别为11.343 mg· mL-1和9.386 mg· mL-1,Vmax分别为0.406 mg（mL·min）-1和1.079 mg（mL·min）-1;糖化酶的Km分别为10.307 mg· mL-1和8.905 mg·mL-1,Vmax分别为0.338 mg（mL·min）-1和0.821mg（mL·min）-1;水解产物葡萄糖对反应体系具有竞争性抑制剂的作用,其抑制常数Ki分别为1.298 mg·mL-1和0.934 mg·mL-1.研究结果表明辐照有效提高了马铃薯淀粉的酶解反应活性.     

In vitro and in vivo digestion of octenyl succinic starch

This study aimed to understand effects of octenyl succinic anhydride (OSA) modification of normal corn (NCS) and high-amylose corn (HA7) starch on their enzymatic hydrolysis rates. After modification with 3% and 10% OSA, resistant starch (RS) contents of the cooked OS-NCS increased from 0.8% of the control starch to 6.8% and 13.2% (Englyst Method), respectively, whereas that of the cooked OS-HA7 decreased from 24.1% to 23.7% and 20.9%, respectively. When the cooked NCS, HA7 and OS (10%)-HA7 were used to prepare diets for rats at 55% (w/w) starch, RS contents of the diets were 1.1%, 13.2% and 14.6%, respectively. After feeding to the rats, 20.2–31.1% of the starch in the OS (10%)-HA7-diet was not utilized in vivo and was found in rat feces, which was substantially larger than that of the HA7-diet (≤4.9%) and NCS-diet (≤0.2%). The body weights of the rats, however, remained similar between different groups.     

Construction of combinatorial library of starch-binding domain of Rhizopus oryzae glucoamylase and screening of clones with enhanced activity by yeast display method

Most of the glucoamylases (GA), which catalyze the hydrolysis of -1,4 and -1,6 glycosidic linkages, have a distinct region called a starch-binding domain (SBD). We have developed a powerful method for screening a library of GA mutants by a combination of GA display and SBD mutagenesis on the yeast-cell surface. In the case of Rhizopus oryzae glucoamylase (RoGA), three amino acids (63S, 71T, 73S) of the SBD were combinatorially mutated to enhance the degradation activity toward cooked corn starch and the mutated RoGAs were displayed on yeast-cell surface by cell-surface engineering. After the first screening by halo assay using an iodine-starch reaction, about 200 of the 8000 colonies formed clear halos. Incubation of the yeast with the mutated and displayed RoGAs caused direct degradation of cooked corn starch. Repeated screening revealed that some of the mutants produced a degradation rate around 1.4-fold higher than did wild type. The results obtained from the DNA sequences of the mutated SBDs indicated that amino-acid residues with a carbonyl group (D, E, Q, N) in the SBD enhance the degradation ability of the GA by enhancing the binding activity of the SBD.     

Effect and aftereffect of gamma radiation pretreatment on enzymatic hydrolysis of wheat straw

Irradiation pretreatment of wheat straw was carried out at different doses by using Co-60 gamma radiation. The weight loss and fragility of wheat straw after irradiation, the combination effect of irradiation and mechanical crushing on enzymatic hydrolysis of wheat straw as well as the aftereffect of irradiation were examined. It is shown that irradiation can cause significant breakdown of the structure of wheat straw. The weight loss of wheat straw increased and the size distribution after crushing moved to fine particles at elevated irradiation doses. The glucose yield of enzymatic hydrolysis of wheat straw increased with increasing doses and achieved the maximum (13.40%) at 500 kGy. A synergistic effect between irradiation and crushing was observed, with a glucose yield of 10.24% at a dose of 500 kGy with powder of 140 mesh. The aftereffect of irradiation had important impact on enzymatic hydrolysis of wheat straw. The aftereffect (at 22nd day) of 400 kGy irradiation accounted for 20.0% of the initial effect for glucose production, and the aftereffects of 50, 100, 200 (at 9th day) and 300 kGy (at 20th day) accounted for 12.9%, 14.9%, 8.9% and 9.1%, respectively, for reducing sugar production.     

Direct fermentation of gelatinized sago starch to acetone–butanol–ethanol by Clostridium acetobutylicum

Direct fermentation of gelatinized sago starch into solvent (acetone–butanol–ethanol) by Clostridium acetobutylicum P262 was studied using a 250 ml Schott bottle anaerobic fermentation system. Total solvent production from fermentation using 30 g sago starch/l (11.03g/l) was comparable to fermentation using corn starch and about 2-fold higher than fermentation using potato or tapioca starch. At the range of sago starch concentration investigated (10–80 g/l), the highest total solvent production (18.82 g/l) was obtained at 50 g/l. The use of a mixture of organic and inorganic nitrogen source (yeast extract + NH₄NO₃) enhanced growth of C. acetobutylicum, starch hydrolysis and solvent production (24.47 g/l) compared to the use of yeast extract alone. This gave the yield based on sugar consumed of 0.45 g/g. Result from this study also showed that the individual concentrations of nitrogen and carbon influenced solvent production to a greater extent than did carbon to nitrogen (C/N) ratio.     

High-concentration alcoholic production from hydrolysate of raw ground corn by a tetraploid yeast strain

Summary The suitable conditions for high-concentration ethanol production from raw ground corn by a tetraploid yeast strain were examined. We found that the glucoamylase preparation which ia usually employed for alcoholic fermentation of cooked starch could effectively saccharify raw ground corn starch.     

High-efficiency, one-step starch utilization by transformed Saccharomyces cells which secrete both yeast glucoamylase and mouse alpha-amylase.

Transformed, hybrid Saccharomyces strains capable of simultaneous secretion of glucoamylase and alpha-amylase have been produced. These strains could carry out direct, one-step assimilation of starch, with conversion efficiency greater than 93% during a 5-day growth period. One of the transformants converted 92.8% of available starch into reducing sugars in only 2 days. Glucoamylase secretion by these strains resulted from expression of one or more chromosomal STA genes derived from Saccharomyces diastaticus. The strains were transformed by a plasmid (pMS12) containing mouse salivary alpha-amylase cDNA in an expression vector containing yeast alcohol dehydrogenase promoter and a segment of yeast 2 micron plasmid. The major starch hydrolysis product produced by crude amylases found in culture broths was glucose, indicating that alpha-amylase and glucoamylase acted cooperatively.     

High-efficiency, one-step starch utilization by transformed Saccharomyces cells which secrete both yeast glucoamylase and mouse alpha-amylase

Transformed, hybrid Saccharomyces strains capable of simultaneous secretion of glucoamylase and alpha-amylase have been produced. These strains could carry out direct, one-step assimilation of starch, with conversion efficiency greater than 93% during a 5-day growth period. One of the transformants converted 92.8% of available starch into reducing sugars in only 2 days. Glucoamylase secretion by these strains resulted from expression of one or more chromosomal STA genes derived from Saccharomyces diastaticus. The strains were transformed by a plasmid (pMS12) containing mouse salivary alpha-amylase cDNA in an expression vector containing yeast alcohol dehydrogenase promoter and a segment of yeast 2 micron plasmid. The major starch hydrolysis product produced by crude amylases found in culture broths was glucose, indicating that alpha-amylase and glucoamylase acted cooperatively.     

Permanent Staining with Iodine Vapor

Sections of cooked rice have been stained with iodine vapor, and the method has given greater permanency than any heretofore reported. The method, which permits the use of a counter-stain, has been applied also to starches, starch pastes, uncooked rice flour, and cooked rice flour. The resulting color is of moderate intensity, so that structure is revealed and the birefringence of ungelatinized starch is not impaired. Preparations made more than a year ago have retained their characteristic blue or lavender color.     

纤维二糖发酵生产丙酮丁醇

分别考察C.acetobutylicum 810705、810706以不同浓度的麸皮和玉米粉添加物作为营养元素,纤维二糖直接进行丙酮丁醇(ABE)发酵的结果,发现2株菌对于玉米粉和麸皮的浓度变化趋势一致,C.acetobutylicum 810706转化率较高。纤维二糖ABE发酵工艺条件表明:玉米粉添加量为总糖含量的30%、底物糖质量浓度60 g/L,pH 6.5、温度35℃时,C.acetobutylicum 810706转化率达到37.38%,总溶剂质量浓度22.43 g/L,比葡萄糖、木糖ABE发酵转化率高。模拟纤维素酶水解产物配制混合糖培养基,其溶剂转化率较单独的葡萄糖、木糖发酵的转化率高,为34.95%。对比纤维素酶水解条件,C.acetobutylicum 810706具有优良的纤维素酶水解同步糖化ABE发酵能力。     

Effect of γ Irradiation on the Microflora of Freshwater Fish: III. Spoilage Patterns and Extension of Refrigerated Storage Life of Yellow Perch Fillets Irradiated to 0.1 and 0.2 Megarad1

Maximal shelf life was determined and microbial flora were compared for irradiated (0.1 and 0.2 Mrad) and nonirradiated yellow perch fillets stored at 1 C. Shelf life was estimated by organoleptic determinations. Microbiological studies included determination of the effects of irradiation on the total aerobic microbial population, lag phase, and rate of growth. Genera of organisms isolated from fillets through the course of microbial spoilage were identified, and the proteolytic activity of the organisms was determined. Plate counts for fish prior to irradiation showed the presence of approximately 10(6) organisms per g of sample. Irradiation to 0.1 and 0.2 Mrad produced 1.4 and 3 logarithm reductions of the initial count, respectively. Irradiation to 0.1 and 0.2 Mrad approximately doubled the product's shelf life. Organisms initially isolated from the nonirradiated fillets, in order of decreasing number, consisted of Flavobacterium, Micrococcus-Sarcina, Achromobacter-Alcaligenes-Mima, Pseudomonas, Microbacterium, Vibrio, Bacillus, Corynebacterium, Lactobacillus, Brevibacterium, and Aeromonas. By the 6th and 9th days of fillet storage, Pseudomonas and the Achromobacter group were the predominant organisms. All members of the genus Flavobacterium, but not all members of the genus Pseudomonas, were proteolytically active on raw fish juice-agar and skim milk-agar media. The Achromobacter group was found to be nonproteolytic on both media. Residual flora of fillets irradiated to 0.1 and 0.2 Mrad consisted of the Achromobacter group, Lactobacillus, Micrococcus-Sarcina, and Bacillus. Their sequence in predominance, however, varied with dose level. Not all proteolytic bacteria in the fillets were eliminated by 0.1 and 0.2 Mrad; proteolytic Micrococcus-Sarcina survived these treatments.     

Acid hydrolysis of native and annealed starches and branch-structure of their Naegeli dextrins

Eight commercial starches, including common corn, waxy corn, wheat, tapioca, potato, Hylon V, Hylon VII, and mung bean starch, were annealed by a multiple-step process, and their gelatinization characteristics were determined. Annealed starches had higher gelatinization temperatures, reduced gelatinization ranges, and increased gelatinization enthalpies than their native starches. The annealed starches with the highest gelatinization enthalpies were subjected to acid hydrolysis with 15.3% H2SO4, and Naegeli dextrins were prepared after 10 days' hydrolysis. Annealing increased the acid susceptibility of native starches in the first (rapid) and the second (slow) phases with potato starch showing the greatest and high amylose starches showing the least changes. Starches with a larger shift in onset gelatinization temperature also displayed a greater percent hydrolysis. The increase in susceptibility to acid hydrolysis was proposed to result from defective and porous structures that resulted after annealing. Although annealing perfected the crystalline structure, it also produced void space, which led to porous structures and possible starch granule defects. The molecular size distribution and chain length distribution of Naegeli dextrins of annealed and native starches were analyzed. The reorganization of the starch molecule during annealing occurred mainly within the crystalline lamellae. Imperfect double helices in the crystalline lamellae improved after annealing, and the branch linkages at the imperfect double helices became protected by the improved crystalline structure. Therefore, more long chains were observed in the Naegeli dextrins of annealed starches than in native starches.     

Process development of starch hydrolysis using mixing characteristics of Taylor vortices

In food industries, enzymatic starch hydrolysis is an important process that consists of two steps: gelatinization and saccharification. One of the major difficulties in designing the starch hydrolysis process is the sharp change in its rheological properties. In this study, Taylor–Couette flow reactor was applied to continuous starch hydrolysis process. The concentration of reducing sugar produced via enzymatic hydrolysis was evaluated by varying operational variables: rotational speed of the inner cylinder, axial velocity (reaction time), amount of enzyme, and initial starch content in the slurry. When Taylor vortices were formed in the annular space, efficient hydrolysis occurred because Taylor vortices improved the mixing of gelatinized starch with enzyme. Furthermore, a modified inner cylinder was proposed, and its mixing performance was numerically investigated. The modified inner cylinder showed higher potential for enhanced mixing of gelatinized starch and the enzyme than the conventional cylinder.     

Changes in the Microflora of Irradiated Petrale Sole (Eopsetta jordani) Fillets Stored Aerobically at 0.5 C

The microfloral changes on irradiated petrale sole fillets during aerobic (packaged with oxygen-permeable film), refrigerated storage were determined by the identification of bacterial and yeast isolates to the generic level. The samples were irradiated at 0.0, 0.1, 0.15, 0.2, 0.3, and 0.4 Mrad by use of a cobalt-60 gamma source, were stored at 0.5 C, and were examined periodically for spoilage, total microbial population, and composition. The preirradiation flora of the fresh fillets consisted of coryneforms, Achromobacter, Micrococcus, Flavobacterium, Pseudomonas, and Lactobacillus. Immediately after irradiation, Micrococcus, Achromobacter, coryneforms, and Bacillus were predominant. The flora of the nonirradiated fillets at the time of spoilage consisted of Pseudomonas and Achromobacter. The flora of the irradiated fillets at the time of spoilage consisted of Achromobacter and Trichosporon.     

Acetone–butanol–ethanol production from corn stover pretreated by alkaline twin-screw extrusion pretreatment

In this study, the alkaline twin-screw extrusion pretreated corn stover was subjected to enzymatic hydrolysis after washing. The impact of solid loading and enzyme dose on enzymatic hydrolysis was investigated. It was found that 68.2 g/L of total fermentable sugar could be obtained after enzymatic hydrolysis with the solid loading of 10 %, while the highest sugar recovery of 91.07 % was achieved when the solid loading was 2 % with the cellulase dose of 24 FPU/g substrate. Subsequently, the hydrolyzate was fermented by Clostridium acetobutylicum ATCC 824. The acetone–butanol–ethanol (ABE) production of the hydrolyzate was compared with the glucose, xylose and simulated hydrolyzate medium which have the same reducing sugar concentration. It was shown that 7.1 g/L butanol and 11.2 g/L ABE could be produced after 72 h fermentation for the hydrolyzate obtained from enzymatic hydrolysis with 6 % solid loading. This is comparable to the glucose and simulated hydrozate medium, and the overall ABE yield could reach 0.112 g/g raw corn stover.     

Optimization of conditions for production of sago starch-based foam

Production of sago starch-based foam involved mixing of sago starch with polyvinyl alcohol (PVA) or polyvinyl pyrrolidone (PVP) followed by preparation of electron beam irradiated sago starch/PVA and sago starch/PVP sheets and expanding them in a microwave. The results revealed that good foams with high linear expansion and closed cell structure can be produced from 25:15 of sago starch:PVA and 30:10 of sago starch:PVA blends prepared at 80 °C and electron beam irradiated at 15 kGy or 10 kGy for the cross-linking process. An increment of sago starch in the blends enhanced the linear expansion of the foams produced. Change in the blend morphology was observed when it was exposed to higher irradiation doses as electron beam irradiation induced the cross-linking in PVA and PVP, and leaching of amylose and amylopectin from the starch granules. Sago starch/PVA blend is more suitable for foam production because it produced flexible and glossy foam as compared to sago starch/PVP blend which produced very rigid foam.     

Ethanol production from non-starch carbohydrates of wheat bran

Wheat bran (WB), produced worldwide in large quantities as a by-product of the wheat milling industry, constitutes a significant underutilized source of sugars. This paper describes various methods of hydrolyzing the abundant polysaccharides in bran to yield a sugar feedstock suitable for fermentation into bioethanol. Firstly, the starch in the bran was released using amylolytic enzymes. The fibrous material remaining was further hydrolyzed. Acid hydrolysis, heat pretreatment followed by enzymatic hydrolysis and direct enzymatic hydrolysis were compared in terms of total sugar yield and pentose sugar yield. The maximum total sugar yield was achieved when small amounts of acid were added at the pretreatment step prior to enzymatic hydrolysis. This form of pretreatment released most pentosans and significantly enhanced the hydrolysis of cellulose. The overall sugar yield of this combined hydrolysis method reached 80% of the theoretical and it consisted of 13.5 g arabinose, 22.8 g xylose and 16.7 g glucose per 100 g starch-free bran.     

Amylolysis of raw corn by Aspergillus niger for simultaneous ethanol fermentation

The novelty of this approach was hydrolysis of the raw starch in ground corn to fermentable sugars that are simultaneously fermented to ethanol by yeast in a non-sterile environment. Thus, the conventional cooking step can be eliminated for energy conservation. A koji of Aspergillus niger grown on whole corn for 3 days was the crude enzyme source. A ratio of 0.2 g dry koji/g total solids was found sufficient. Optimum pH was 4.2. Ethanol concentration was 7.7% (w/w) in the aqueous phase with 92% raw starch conversion. Agitation increased rate. Sacharification was the rate-limiting step. The initial ethanol concentration preventing fermentation was estimated to be 8.3% by weight.