Fractionation of flax shives with pressurized aqueous ethanol

Fractionation of flax shives into major biopolymer constituents, such as cellulose, hemicelluloses, and lignin, was carried out with pressurized aqueous ethanol in a pressurized low-polarity water extractor. The effect of processing parameters such as temperature, ethanol concentration, flow rate, sample size and solvent/feed ratio on the simultaneous extraction of hemicelluloses and lignin was determined. More than 80% of total hemicelluloses and ∼78% of total lignin were removed simultaneously in a single step under the following conditions: 180 °C, 30% (v/v) ethanol concentration, 3 mL/min flow rate, and 45 mL/g solvent/feed ratio. Under these extraction conditions, cellulose degradation was negligible. Further, the separation of lignin from hemicelluloses was carried out using two simple alternative methodologies based on precipitation. Since no acidic or alkali catalysts were used, the degradation of biopolymers was negligible and the oligomer/monomer ratio of sugars was 825:1. Characterization of fractionated biopolymers was carried out with scanning electron microscopy and a Fourier-transform infrared spectrometer (FT-IR). FT-IR spectra of isolated lignin and hemicelluloses showed that both polymers were comparable to commercially available products.     

Thermochemical characterisation of straws and high yielding perennial grasses

The research is concerned with thermochemical characterisation of straws and high yielding perennial grasses. Crops selected for this study include wheat straw (Triticum aestivum), rape straw (Brassica napus), reed canary grass (Phalaris arundinacea) and switch grass (Panicum virgatum). Thermogravimetric analysis (TGA) was used to examine the distribution of char and volatiles during pyrolysis up to 900 °C. Utilising multi-heating rate thermogravimetric data, the Friedman iso-conversional kinetic method was used to determine pyrolysis kinetic parameters. Light and medium volatile decomposition products were investigated using pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) up to 520 °C. The 22 highest yielding identifiable cellulose, hemicellulose and lignin biomass markers were semi-quantified taking into consideration peak areas from GC chromatograms. Notable differences can be seen in butanedioic acid, dimethyl ester (hemicelluloses decomposition products), 2-methoxy-4-vinylphenol (lignin marker) and levoglucosan (intermediate pyrolytic decomposition product of cellulose) content when comparing perennial grasses with straw. From results presented in this study, perennial grasses such as switch grass, have the most attractive properties for fast pyrolysis processing. This is because of the observed high volatile yield content of 82.23%, heating value of 19.64 MJ/kg and the relatively low inorganic content.     

Dissolving lignocellulosic biomass in a 1-butyl-3-methylimidazolium chloride-water mixture

An ionic liquid (IL)-water mixture employed to treat lignocellulosic biomass is promising. The addition of water decreases viscosity and process cost so as to improve the IL practical application. In this work, effects of temperature (50-170 °C), water content (0-80 wt%), treating duration (0.5-4 h) and pressure (0.1-3.2 MPa) on treating legume straw process using a 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl)-water mixture were experimentally investigated. Legume straw was found to be partially dissolved, and the dissolved substances can be flocculated by adding the coagulating agent—water (equal to volume of the solution). For this process at 0.1 MPa, the maximum 29.1 wt% legume straw is dissolved in the [C₄mim]Cl-water mixture with water content of 20 wt% at 150 °C during 2 h, which is much higher than 9.8 wt% using pure [C₄mim]Cl. A hemicellulose-free lignin-rich material (64.0 wt% lignin and 35.3 wt% cellulose) is obtained by adding the water. Even for 0.5 h, 22.3 wt% of legume straw is dissolved in the case of water content of 20 wt%, 150 °C and 0.1 MPa. High pressure favors the dissolution of legume straw but lignin content in the residue has no obvious change. The addition of proper amount of water facilitates the dissolution of legume straw and a relative rapid dissolving rate can be achieved in a [C₄mim]Cl-water mixture. There are great differences in chemical and physical properties between legume straw and the obtained samples (residue and floc) due to the dissolution and reconstitution.     

Effect of pre-extraction on soda-anthraquinone (AQ) pulping of rice straw

The effect of hot-water and alkaline pre-extraction of rice straw on soda-anthraquinone pulping was carried out. The pre-extraction with hot water at 150 °C for 1 h dissolved 34.7% biomass and the pre-extracted liquor comprised of 16.6% sugars, 6.7% lignin, 6.6% acetic acid and other unknown products. But the pre-extraction with 1% NaOH at 100 °C for 1 h dissolved 10.2% sugars, 5.1% lignin and 10% acetic acid from rice straw. Pre-extracted rice straw was cooked by soda-anthraquinone process with varying alkali charges. The pulp from pre-extracted rice straw was low in kappa number with reduced pulp yield. The drainage resistance (°SR) improved obviously on pre-extraction of rice straw. Pulp strength properties such as the tensile index and the burst index were found to be lower, but the tear index was higher both with hot-water and alkaline pre-extraction. After bleaching, the gaps of the overall pulp yield and strength properties between pre-extracted and non-extracted rice straw became narrower. The alkaline pre-extraction showed improved yield and properties compared with hot-water pre-extracted rice straw.     

Structural characterization and isolation of lignin and hemicelluloses from barley straw

Structural characterization and isolation of lignin and hemicelluloses from crops are very important for industrial utilization. In this paper, the sequential treatments of barley straw using 90% dioxane, 80% acidic dioxane, 100% dimethyl sulfoxide, and 8% NaOH released total 93% of original lignin and 87% of original hemicelluloses. The extractions with acidic dioxane and dimethyl sulfoxide produced the original hemicelluloses and high-condensed lignin mainly from the middle lamella. FT-IR and NMR analyses show that the hemicelluloses of barley straw contain acidic arabinxylans as the major polysaccharides, which are substituted by α-l-arabinofuranose, 4-O-methyl-glucuronic acid, acetyl group (DS = 0.13), and xylose at O-3 and/or O-2 of xylan, and lignin contains β-O-4′ as a predominant interunit linkage with high amounts of β-5′ and β-1′. The guaiacyl and syringyl units are more etherified, and the proportion of erythro-β-O-4′ is slightly higher than that of threo-β-O-4′ in the lignin of barley straw.     

Processing of Lespedeza stalks by pretreatment with low severity steam and post-treatment with alkaline peroxide

The steam pre-treatment with low severity preserves valuable biomass components, and further delignification with alkaline peroxide could improve hydrolysis. A combination of low severity steam pretreatment and alkaline peroxide post-treatment of Lespedeza stalks was investigated. The post-treatment of steam-pretreated Lespedeza stalks with alkaline peroxide significantly increased the cellulose content and changed the structure of the cellulose-rich fractions. A glucose yield of 503.5 mg g⁻¹ raw material from enzyme hydrolysis was obtained when the steam-pretreated material (184 °C for 4 min) was post-treated with 2% hydrogen peroxide at 60 °C for 24 h with a substrate concentration of 3.3%. Its hydrolysis yield is 88.8%, which is higher than that of samples processed by steam pretreatment alone (63.7%). The samples obtained by post-treatment with alkaline peroxide were found to have a smoother surface and looser structure in scanning electron microscopy images. The isolated lignin preparations had a yield range from 10.9 to 14.7 (% dry matter). The lignin was characterized by thermogravimetric analysis/differential thermal analysis, Fourier transform infrared spectroscopy, and gel permeation chromatography. Alkaline peroxide treatment increased the thermal stability of lignin, and decreased the amounts of all functional groups. Depolymerization and repolymerization occurred during the alkaline peroxide treatment.     

Effect of heat on rheology,surface hydrophobicity and molecular weight distribution of glutens extracted from flours with different bread-making quality

Gluten was extracted from flours of several different wheat varieties of varying baking quality. Creep compliance was measured at room temperature and tan δ was measured over a range of temperatures from 25 to 95 °C. The extracted glutens were heat-treated for 20 min at 25, 40, 50, 60, 70 and 90 °C in a water bath, freeze-dried and ground to a fine powder. Tests were carried out for extractability in sodium dodecyl sulphate, free sulphydryl (SH) groups using Ellman's method, surface hydrophobicity and molecular weight (MW) distribution (MWD) using field-flow fractionation and multi-angle laser light scattering. With increasing temperature, the glutens showed a decrease in extractability, with the most rapid decreases occurring between 70 and 90 °C, a major transition in tan δ at around 60 °C and a minor transition at 40 °C for most varieties, a decrease in free SH groups and surface hydrophobicity and a shift in the MWD towards higher MW. The poor bread-making variety Riband showed the highest values of tan δ and Newtonian compliance, the lowest content of free SH groups and the largest increase of HMW/LMW with increasing temperature. No significant correlations with baking volume were found between any of the measured parameters.     

Ester and ether linkages between hydroxycinnamic acids and lignins from wheat,rice, rye,and barley straws,maize stems,and fast-growing poplar wood

Treatment of solvent extracted wheat, rice, rye, and barley straws, maize stems, and fast-growing poplar wood with 60% aqueous ethanol in 0.2 M HCl at 75 °C for 3 h released 51.8, 51.2, 47.2, 43.7, 54.0, and 16.7% of the original lignin, and 44.3, 50.3, 30.9, 36.1, 40.0, and 25.5% of the original hemicelluloses, respectively. It was found that the bulk of p-coumaric acid (PCA) (67.0–83.5%) was esterified at the lignin side chains, while ferulic acid (FA) is linked to lignin side chains through both ether bonds (51.6–68.3%) and ester bonds (31.7–48.4%), indicating that FA may form intra- and/or inter-molecular ester–ether bridges between lignin fragments, which is first proposed in this study. In addition to p-hydroxybenzoic acid esterified to lignins in the cell walls of wheat straw and fast-growing poplar wood, a small portion of ether-linked p-hydroxybenzoic acid in the lignin preparations, obtained from rice, rye, and barley straws and maize stems, was also detected. It was also detected that noticeable amounts of syringic and vanillic acids were predominantly esterified to the lignin molecules in the cell walls of the materials studied.     

Temperature-induced structural and chemical changes in cork from Quercus cerris

The effects of temperature on anatomical and chemical characteristics of Quercus cerris cork were examined. Cork samples were subjected to isothermal air heating between 150 °C and 400 °C and analyzed for mass loss, cellular structure and chemical composition.The thermal decomposition of Q. cerris cork is similar to that of Q. suber cork. Cork is thermally stable below 200 °C and after that degradation depended on temperature and heating time with increasing mass loss, i.e. 3% at 200 °C 10 min and 46% at 350 °C 60 min. With temperature and starting at 200 °C, cells expanded, cell wall thickness was reduced and corrugations were lost.Extractives degraded at lower temperatures, although aliphatic extractives were found to be more stable. Suberin from Q. cerris was more heat resistant than Q. suber suberin, while lignin showed similar resistance.These results provide a basis for studies on the production of Q. cerris bark expanded cork agglomerates for insulation purposes.     

Partial purification and characterization of polyphenoloxidase from durum wheat (Triticum durum L.)

A bright yellow color of pasta is an important qualitative trait for the durum wheat industry. Final color is the result of the balance between yellow and brown components in semolina. Polyphenoloxidase (PPO) is implicated as playing a significant role in darkening. This study aimed to characterize PPO activity of durum wheats. PPO was extracted and partially purified by ion-exchange chromatography on a column packed with diethyaminoethyl cellulose (DEAE). This procedure led to 26.33-fold purification with 24.7% recovery. The optimum temperature and pH of PPO were found to be 40 °C and 6.5, respectively. Heat stability of durum wheat PPO decreased as the temperatures increased from 30 to 80 °C. The z-value was calculated as 23.4 °C. It increased to 26.3 and 48.4 °C in the presence of 40% sucrose and 1 M NaCl, respectively. Durum wheat PPO was shown to use several phenolic compounds as substrate. Among the substrates used, the greatest substrate specificity was observed with catechol. Durum wheat PPO was sensitive to inhibitors such as ascorbic acid, cysteine, oxalic acid and citric acid. Ascorbic acid was the most effective inhibitor.     

Extraction of flax shive using sodium ethoxide catalyst in anhydrous ethanol

This work investigated the yield and nature of solvent-soluble organic compounds extracted from flax shive using a room temperature reaction (20 °C) with sodium ethoxide catalyst at four different concentrations (0.2, 0.5, 0.7, and 1.0 M) in anhydrous ethanol. Results were compared with the use of aqueous sodium hydroxide (1.0 M) at two different reaction temperatures (20 °C and 100 °C). Quantitative yield from flax shive varied linearly with sodium ethoxide concentration and averaged 54.5 mg/g on a dry-mass basis (db) at 1.0 M. In contrast, the quantitative yield using 1.0 M sodium hydroxide was much lower, averaging 2.2 mg/g (db). Yield did not differ significantly due to changes of particle size in either case, or due to changes of temperature over the range considered in the case of sodium hydroxide.Analyses using proton nuclear magnetic resonance (¹H NMR) confirmed all extracts to contain aromatic compounds, thus likely lignin derived, but found differences in chemical characteristics between the two extraction methods. One key difference was the presence of compounds with methyl ether groups in sodium hydroxide extracts that were absent in the case of sodium ethoxide extracts. Given that flax contains a mixed guaiacyl-syringyl lignin, methyl ether groups would be expected to be present. Control reactions on three model compounds were carried out to confirm that transesterification occurred with sodium ethoxide. These control reactions also demonstrated that methyl ether groups would be expected to remain intact under the extraction conditions reported here. In light of the higher yield of solvent soluble compounds recovered by extraction with basic ethanol, flax shive may represent a source of value-added phenolic constituents. This processing method may also represent a useful pre-treatment prior to the production of biofuels by cellulose degrading organisms.     

Bioprocess preparation of wheat straw fibers and their characterization

Plant fiber reinforced thermoplastic composites have gained much attraction in structural applications such as building and automotive products. Agricultural residues such as wheat straw, bagasse, and corn stover can also be exploited as readily available natural fiber resources for similar applications. The objective of this study was to extract fibers from wheat straw and also to determine the usefulness of fungal retting of wheat straw before extracting the fibers. Wheat straw was mechanically defibrillated using a laboratory-scale mechanical refiner before and after fungal retting. Fiber characteristics such as physico-chemical and mechanical properties, surface characteristics, and thermal properties of the resultant fibers were measured in order to explore the possibilities of using the fibers as reinforcing materials. Retted fibers were stronger than un-retted fibers. The length and diameter of the retted fibers were lower than the un-retted fibers. FT-IR spectroscopic analysis of the wheat straw fibers indicated the fractional removal of hemicelluloses and lignin from the retted fiber. X-ray photoelectron spectroscopy (XPS) of the fibers showed the partial removal of extractives from the surface of the retted fibers. Also, the oxygen to carbon ratio (O/C) of the fibers illustrated that there is more lignin type surface structure for both retted and un-retted fibers. However, slightly higher ratio of oxygen to carbon in the retted fiber indicated a more carbohydrate-rich fiber than the un-retted fiber. Thermal degradation characteristics demonstrated the suitability of processing wheat straw fibers with thermoplastics.     

Effects of transition season management on soil N dynamics and system N balances in rice–wheat rotations of Nepal

In the low-input rice–wheat production systems of Nepal, the N nutrition of both crops is largely based on the supply from soil pools. Declining yield trends call for management interventions aiming at the avoidance of native soil N losses. A field study was conducted at two sites in the lowland and the upper mid-hills of Nepal with contrasting temperature regimes and durations of the dry-to-wet season transition period between the harvest of wheat and the transplanting of lowland rice. Technical options included the return of the straw of the preceding wheat crop, the cultivation of short-cycled crops during the transition season, and combinations of both. Dynamics of soil N_min, nitrate leaching, nitrous oxide emissions, and crop N uptake were studied throughout the year between 2004 and 2005 and partial N balances of the cropping systems were established. In the traditional system (bare fallow between wheat and rice) a large accumulation of soil nitrate N and its subsequent disappearance upon soil saturation occurred during the transition season. This nitrate loss was associated with nitrate leaching (6.3 and 12.8 kg ha⁻¹ at the low and high altitude sites, respectively) and peaks of nitrous oxide emissions (120 and 480 mg m⁻² h⁻¹ at the low and high altitude sites, respectively). Incorporation of wheat straw at 3 Mg ha⁻¹ and/or cultivation of a nitrate catch crop during the transition season significantly reduced the build up of soil nitrate and subsequent N losses at the low altitude site. At the high altitude site, cumulative grain yields increased from 2.35 Mg ha⁻¹ with bare fallow during the transition season to 3.44 Mg ha⁻¹ when wheat straw was incorporated. At the low altitude site, the cumulative yield significantly increased from 2.85 Mg ha⁻¹ (bare fallow) to between 3.63 and 6.63 Mg ha⁻¹, depending on the transition season option applied. Irrespective of the site and the land use option applied during the transition season, systems N balances remained largely negative, ranging from −37 to −84 kg N ha⁻¹. We conclude that despite reduced N losses and increased grain yields the proposed options need to be complemented with additional N inputs to sustain long-term productivity.     

Comparative study of organosolv lignins from wheat straw

Dewaxed wheat straw was treated with acetic acid–H₂O (65/35, v/v), acetic acid–H₂O (80/20, v/v), acetic acid–H₂O (90/10, v/v), formic acid–acetic acid–H₂O (20/60/20, v/v/v), formic acid–acetic acid–H₂O (30/60/10, v/v/v), methanol–H₂O (60/40, v/v) and ethanol–H₂O (60/40, v/v) using 0.1% HCl as a catalyst at 85 °C for 4 h, in which 78.2, 80.0, 88.2, 89.4, 94.1, 23.5 and 37.4% of the original lignin, and 42.4, 58.7, 70.0, 65.1, 76.5, 14.2 and 22.2% of the original hemicelluloses was released, respectively. Lignins obtained were characterized by their content of hemicelluloses, composition of phenolic acids and aldehydes, molecular weight, thermal stability and by UV, Fourier transform infrared (FT-IR), ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The results showed that aqueous organic acid was more effective than aqueous organic alcohol for extensive delignification and selective fractionation of cellulose, lignin and hemicelluloses from the straw. In particular, the addition of formic acid gave a significant effect on the dissolution of lignin. All the acid-insoluble lignin fractions contained small amounts of contaminated hemicelluloses as shown by their content of neutral sugars, 0.9–4.3%, and had weight-average molecular weight between 3960 and 4340 g mol⁻¹. An increase in concentration of acetic acid or formic acid in organosolv resulted in an increment in release of guaiacyl units and in lignin condensation. However, the lignin preparations released during the treatment with aqueous organic alcohol without organic acid contained almost equal amounts of non-condensed guaiacyl and syringyl units with fewer p-hydroxyphenyl units. The β-O-4 ether bonds together with β-β, β-5 and 5-5′ carbon–carbon linkages were identified to be present in lignin substructures.     

Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20–85 °C) or pressure/heat combinations (100–600 MPa at 20, 40 and 50 °C) for 15 min to investigate their gelatinization and rheological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 °C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 °C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 °C, 500 MPa at 50 °C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G′) dramatically increased from 70 °C or 400 MPa. The G′ values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible.     

Characteristics, composition and thermal stability of Acacia senegal (L.) Willd. seed oil

The chemical composition, main physicochemical properties and thermal stability of oil extracted from Acacia senegal seeds were evaluated. The oil, moisture and the ash contents of the seeds were 9.80%, 6.92% and 3.82%, respectively. Physicochemical properties of the oil were iodine value, 106.56 g/100 g of oil; saponification value, 190.23 mg KOH/g of oil; refractive index (25 °C), 1.471; unsaponifiable matter, 0.93%; acidity, 6.41% and peroxide value, 5.43 meq. O₂/kg of oil. The main fatty acids in the oil were oleic acid (43.62%) followed by linoleic acid (30.66%) and palmitic acid (11.04%). The triacylglycerols (TAGs) with equivalent carbon number ECN 44 (34.90%) were dominant, followed by TAGs ECN 46 (28.19%), TAGs ECN 42 (16.48%) and TAGs ECN 48 (11.23%). The thermal stability analysed in a normal oxidizing atmosphere showed that the oil decomposition began at 268.6 °C and ended at 618.5 °C, with two stages of decomposition at 401.5 °C and 576.3 °C. According to these results, A. senegal seed oil has physicochemical properties, fatty acids composition and thermal characteristics that may become interesting for specific applications in several segments of food and non-food industries.     

Sequential extractions and structural characterization of lignin with ethanol and alkali from bamboo (Neosinocalamus affinis)

A sequential process with the combination of ethanol and alkali aqueous solutions was utilized to extract lignin from bamboo (Neosinocalamus affinis), a potential lignocellulosic material. In this case, the successive treatments of dewaxed bamboo with 70% ethanol at 80 °C, 0.2 and 0.5 M NaOH, 70% ethanol containing 0.6 M NaOH, and 1.0, 2.0, and 3.0 M NaOH at 50 °C, resulted in a total yield of acid-insoluble lignin fractions of 10.06%, corresponding to release of 62.25% original lignin from the cell walls. The lignin fractions obtained were then characterized by GPC, FT-IR, NMR spectroscopy, and sugar analysis. As compared to the alkali lignin fractions, the ethanol-soluble lignin fraction had a relatively higher molecular weight (2670 g/mol) and the content of carbohydrates primarily consisted of glucose 2.01% and xylose 1.90%. This suggested that the carbohydrate chains linked to lignin may increase the hydrodynamic volume of lignin and therefore increase the apparent molecular weight of the ethanol-soluble lignin. HSQC spectra analysis revealed that the alkali lignin fractions consisted mainly of β-O-4′ linkages combined with small amounts of β-β′, β-5′, β-1′ linkages, and p-hydroxycinnamyl alcohol end groups. Furthermore, minor amounts of esterified p-coumaric and ferulic acids were also detected in the lignins isolated.     

Thermogravimetric analysis and the optimisation of bio-oil yield from fixed-bed pyrolysis of rice husk using response surface methodology (RSM)

The effects of pyrolysis temperature, heating rate, particle size, holding time, and gas flow rate were investigated to optimize bio-oil yield from rice husk pyrolysis. Thermogravimetric analysis showed thermal degradation of hemicellulose, cellulose and lignin, indicating faster decomposition of cellulose compared to lignin. The optimisation process was analysed by employing central composite design (CCD) in response surface methodology (RSM) using Design Expert Version 7.5.1 (StatEase, USA). A two-level fractional factorial was initially carried out and followed by RSM. The statistical analysis showed that pyrolysis temperature, heating rate, particle size and holding time significantly affected the bio-oil yield. By utilising response surface method, these four factors were investigated, analysed and optimal conditions were obtained at pyrolysis temperature of 473.37 °C, heating rate of 100 °C/min, particle size of 0.6 mm and holding time of 1 min. Confirmation runs gave 48.30% and 47.80% of bio-oil yield compared to 48.10% of predicted value. Furthermore, the pyrolytic bio-oils obtained from fixed-bed pyrolysis were examined using gas chromatographic/mass spectroscopy (GC/MS), Fourier transform infrared (FTIR) methods, elemental analyzer, pH probe and bomb calorimeter.     

Pretreatment of partially delignified hybrid poplar for biofuels production: Characterization of organosolv hemicelluloses

In this study, extraction of hemicelluloses from the carbohydrate-enriched residues was successfully carried out with organic solvent and the residue was used for bio-based energy production. The chemical composition and physico-chemical properties of six hemicelluloses released were elucidated by a combination of sugar analysis, molecular determination, Fourier transform infrared, and ¹H, ¹³C and 2D-HSQC NMR spectroscopy. The results showed that the successful treatments resulted in a fractionation of the native hemicelluloses. The sugar analysis indicated that xylose (47.14-56.91%) was found to be the major sugar components and small amounts of glucose (14.1-19.06%) and mannose (12.41-18.09%) were also observed in these hemicellulosic fractions. Further studies by NMR spectroscopy exhibited that the acetylated hemicellulosic fraction had a main structure of (1 → 4)-linked β-d-xylopyranosyl backbone with 4-O-methyl-α-d-glucuronic acid as a side chain and a minor structure of linear β-(1 → 4)-linked glucomannans. Furthermore, these hemicelluloses possessed a low substituted degree which was beneficial for enzymatic saccharification.     

Dough/crumb transition during French bread baking

The modifications occurring during dough to crumb (D/C) transition of French bread (350 g) were studied in an instrumented pilot-scale oven for doughs with different contents of minor components, soluble, lipids and puroindolines. Internal temperature measurements showed that, for most compositions, complete D/C transition occurred between 55 and 70 °C, after 5 min of baking, and coincided with maximum loaf expansion. Differential scanning calorimetry (DSC) in excess of water performed on samples taken during baking (3 and 5 min) showed that starch gelatinization and melting developed continuously during D/C transition for various contents of the soluble fraction in dough. Dynamic thermomechanical analysis (DMA) on dough showed that dough stiffened between 60 and 70 °C, as seen by the increase of elastic modulus E′ by more than one decade, for all dough compositions. Relating these changes to the results of baking experiments, D/C transition was assigned first to gluten reticulation and, to a lesser extent, to continuous starch granule swelling.