Loss Of Xylan Research Articles

Evaluation of Ammonia Pretreatment for Enzymatic Hydrolysis of Sugarcane Bagasse to Recover Xylooligosaccharides.

Sugarcane bagasse is a useful biomass resource. In the present study, we examined the efficacy of ammonia pretreatment for selective release of hemicellulose from bagasse. Pretreatment of bagasse with aqueous ammonia resulted in significant loss of xylan. In contrast, pretreatment of bagasse with anhydrous ammonia resulted in almost no xylan loss. Aqueous ammonia or anhydrous ammonia-pretreated bagasse was then subjected to enzymatic digestion with a xylanase from the glycoside hydrolase (GH) family 10 or a xylanase from the GH family 11. The hydrolysis rate of xylan in bagasse pretreated with aqueous ammonia was approximately 50 %. In contrast, in the anhydrous ammonia-treated bagasse, xylan hydrolysis was > 80 %. These results suggested that anhydrous ammonia pretreatment would be an effective method for preparation of sugarcane bagasse for enzymatic hydrolysis to recover xylooligosaccharides.

Pretreatment of Sweet Sorghum Bagasse for Ethanol Production Using Na2CO3 Obtained by NaOH Absorption of CO2 Generated in Sweet Sorghum Juice Ethanol Fermentation

(1) Background: Commercial production of fuel ethanol currently uses sugarcane and corn as feedstocks. Attempts to develop other renewable feedstocks that are more abundant have led to lignocellulosic biomass, which requires pretreatment prior to enzymatic hydrolysis to generate fermentable sugars. One of the largest cost components of pretreatment is chemical cost. Ethanol fermentation also produces large quantities of CO2 as a co-product contributing to global warming. (2) Methods: Sweet sorghum has emerged as a potential new feedstock for ethanol production. In the present study, the CO2 produced in sweet sorghum juice (SSJ) fermentation was captured by absorption in 5 M NaOH. The resultant Na2CO3 solution was used for pretreatment of sweet sorghum bagasse (SSB), which is the solid residue in SSJ extraction. The pretreated SSB was fermented in SSJ to produce additional ethanol. (3) Results: CO2 absorption efficiency of 92.0% was observed. Pretreatment of SSB by the obtained Na2CO3 solution resulted in no loss of glucan and only 8.1 wt% loss of xylan. Ethanol yield from glucan in the pretreated SSB was 81.7% theoretical. (4) Conclusions: CO2 from SSJ fermentation captured as Na2CO3 could be used for efficient SSB pretreatment. Further study focusing on pretreatment process optimization is needed.

Alkaline and fungal pretreatments for improving methane potential of Napier grass

Alkaline and biological pretreatments were compared for enhancing the biological methane potential of Napier grass. The earlier reported biotreatments for Napier grass did not use the edible white-rot fungus Pleurotus sajor-caju, as in the present work. Dry Napier grass was ground to different particles sizes (20–30 mm, N1-L; ≤0.6 mm, N1-S). The N1-L grass was treated with alkali and designated as the alkali treated grass N2. The samples N1-S, N1-L and N2 were used separately as substrates for growing the fungus for 14 days at room temperature (30 ± 2 °C) in a solid-state biotreatment. Alkali treatment delignified the grass 2.1- to 10.7-fold better than the fungus. Fungal treatment resulted in 3.8- to 8.3-fold loss in glucan compared to alkali treatment. Maximum xylan loss occurred in the N1-S fine-ground grass after fungal growth. The fungus-grown grass samples (N1-FL, N1-FS, N2-F), the untreated ground samples (N1-L, N1-S) and the alkali treated sample (N2) were anaerobically digested to determine the biological methane potential. The fungus-grown grass samples had a maximum daily methane production in the range of 44–50 cm3 g VS−1, significantly higher than the samples not treated with the fungus. The alkali treated grass gave a significantly higher cumulative methane yield than the untreated grass and the biological methane potential was ∼71–77% of the theoretical methane potential. The proportion of methane in the total gas produced from the treated grass was in range of 74–83% by volume whereas it was 57–68% for the untreated grass.

Simplified sodium chlorite pretreatment for carbohydrates retention and efficient enzymatic saccharification of silvergrass

In this work, a simplified and cost-effective chlorite pretreatment method to improve the hydrolysabiliy of biomass was developed. Compared to common used sodium chlorite-acetic acid (SCA) pretreatment (18.1%), sodium chlorite (SC) pretreatment resulted in less xylan loss (7.8%), thus led more carbohydrates retention. Moreover, the Chinese silvergrass pretreated by SC for 2 h achieved higher glucose yield (70.5%) than the substrate pretreated by SCA under the same pretreatment conditions did (58.7%), after 48 h enzymatic hydrolysis by cellulase. By synergistic action of cellulase and xylanase, the glucose yield of SC pretreated (12 h) samples reached to 93.5% with 808.7 mg/g DM total reducing sugars yields. In addition, without the usage of acetic acid could decrease the process cost and result in less inhibitor generation in pretreatment process.

Low acid hydrothermal fractionation of Giant Miscanthus for production of xylose-rich hydrolysate and furfural

Low acid hydrothermal (LAH) fractionation was developed for the effective recovery of hemicellulosic sugar (mainly xylose) from Miscanthus sacchariflorus Goedae-Uksae 1 (M. GU-1). The xylose yield was maximized at 74.75% when the M. GU-1 was fractionated at 180°C and 0.3wt.% of sulfuric acid for 10min. At this condition, the hemicellulose (mainly xylan) degradation was 86.41%. The difference between xylan degradation and xylose recovery yield, i.e., xylan loss, was 11.66%, as indicated by the formation of decomposed products. The furfural, the value added biochemical product, was also obtained by 0.42g/L at this condition, which was 53.82% of furfural production yield based on the xylan loss. After then, the furfural production continued to increase to a maximum concentration of 1.87g/L, at which point the xylan loss corresponded to 25.87%.

TBL3 and TBL31, Two Arabidopsis DUF231 Domain Proteins, are Required for 3-O-Monoacetylation of Xylan.

Xylan, a major constituent of secondary cell walls, is made of a linear chain of β-1,4-linked xylosyl residues that are often substituted with glucuronic acid/methylglucuronic acid side chains and acetylated at O-2 and O-3. Previous studies have shown that ESK1, an Arabidopsis DUF231 protein, is an acetyltransferase catalyzing 2-O- and 3-O-monoacetylation of xylan. However, the esk1 mutation only causes a partial loss of xylan 2-O- and 3-O-monoacetylation, suggesting that additional xylan acetyltransferase activities are involved. In this report, we demonstrated the essential roles of two other Arabidopsis DUF231 genes, TBL3 and TBL31, in xylan acetylation. The expression of both TBL3 and TBL31 was shown to be induced by overexpression of the secondary wall master transcriptional regulator SND1 (secondary wall-associated NAC domain protein1) and down-regulated by simultaneous mutations of SND1 and its paralog NST1, indicating their involvement in secondary wall biosynthesis. β-Glucurondase (GUS) reporter gene analysis showed that TBL3 and TBL31 were specifically expressed in the xylem and interfascicular fibers in stems and the secondary xylem in root hypocotyls. Expression of fluorescent protein-tagged TBL3 and TBL31 in protoplasts revealed their localization in the Golgi, where xylan biosynthesis occurs. Although mutation of either TBL3 or TBL31 alone did not cause any apparent alterations in cell wall composition, their simultaneous mutations were found to result in a reduction in xylan acetylation. Further structural analysis demonstrated that the tbl3 tbl31 double mutant had a specific reduction in 3-O-acetylation of xylan. In addition, the tbl3 tbl31 esk1 triple mutant displayed a much more drastic decrease in 3-O-acetylation of xylan, indicating their functional redundancy in xylan 3-O-acetylation. These findings indicate that TBL3 and TBL31 are secondary wall-associated DUF231 genes specifically involved in xylan 3-O-acetylation.

Cell wall disruption in low temperature NaOH/urea solution and its potential application in lignocellulose pretreatment

Pretreatments of wheat straw by NaOH/urea solvent at low temperature were investigated. To understand the cell wall disruption during this low temperature process, and its impacts on enzymatic hydrolysis, morphology, cellulose crystal structure, and chemical properties were investigated by using the following instruments: optical microscopy, confocal laser scanning microscopy, Fourier transform infrared spectra, and X-ray diffraction. The results implied that the deconstruction of plant cell wall at low temperature was attributed to disruption of the hydrogen bonds in cellulose and solubilization of hemicellulose and lignin. Meanwhile, the pretreatment approach resulted in almost full recovery of cellulose, approximately 60 % of lignin and 70 % of xylan removal, respectively. It’s interesting to note that cellulose I crystal structure in the substrate pretreated at a solid loading of 10 % was partially changed to cellulose II structure, while wheat straw pretreated at a higher solid loading of 20 %, retained the cellulose I structure. Almost complete saccharification (>95 %) of cellulose in pretreated substrates was achieved at a relatively low cellulase loading of 10 FPU/g substrates within 48 h. The loss of xylan in pretreated substrate had a negative effect on the total sugar recovery.

Loss of Arabidopsis GAUT12/IRX8 causes anther indehiscence and leads to reduced G lignin associated with altered matrix polysaccharide deposition.

GAlactUronosylTransferase12 (GAUT12)/IRregular Xylem8 (IRX8) is a putative glycosyltransferase involved in Arabidopsis secondary cell wall biosynthesis. Previous work showed that Arabidopsis irregular xylem8 (irx8) mutants have collapsed xylem due to a reduction in xylan and a lesser reduction in a subfraction of homogalacturonan (HG). We now show that male sterility in the irx8 mutant is due to indehiscent anthers caused by reduced deposition of xylan and lignin in the endothecium cell layer. The reduced lignin content was demonstrated by histochemical lignin staining and pyrolysis Molecular Beam Mass Spectrometry (pyMBMS) and is associated with reduced lignin biosynthesis in irx8 stems. Examination of sequential chemical extracts of stem walls using 2D 13C-1H Heteronuclear Single-Quantum Correlation (HSQC) NMR spectroscopy and antibody-based glycome profiling revealed a reduction in G lignin in the 1 M KOH extract and a concomitant loss of xylan, arabinogalactan and pectin epitopes in the ammonium oxalate, sodium carbonate, and 1 M KOH extracts from the irx8 walls compared with wild-type walls. Immunolabeling of stem sections using the monoclonal antibody CCRC-M138 reactive against an unsubstituted xylopentaose epitope revealed a bi-lamellate pattern in wild-type fiber cells and a collapsed bi-layer in irx8 cells, suggesting that at least in fiber cells, GAUT12 participates in the synthesis of a specific layer or type of xylan or helps to provide an architecture framework required for the native xylan deposition pattern. The results support the hypothesis that GAUT12 functions in the synthesis of a structure required for xylan and lignin deposition during secondary cell wall formation.

Influence of Airflow on Laboratory Storage of High Moisture Corn Stover

Storing high moisture biomass for bioenergy use is a reality in many areas of the country where wet harvest conditions and environmental factors prevent dry storage from being feasible. Aerobic storage of high moisture biomass leads to microbial degradation and self-heating, but oxygen limitation can aid in material preservation. To understand the influence of oxygen presence on high moisture biomass (50 %, wet basis), three airflow rates were tested on corn stover stored in laboratory reactors. Temperature, carbon dioxide production, dry matter loss, chemical composition, fungal abundance, pH, and organic acids were used to monitor the effects of airflow on storage conditions. The results of this work indicate that oxygen availability impacts both the duration of self-heating and the severity of dry matter loss. High airflow systems experienced the greatest initial rates of loss but a shortened microbially active period that limited total dry matter loss (19 %). Intermediate airflow had improved preservation in short-term storage compared to high airflow systems but accumulated the greatest dry matter loss over time (up to 27 %) as a result of an extended microbially active period. Low airflow systems displayed the best performance with the lowest rates of loss and total loss (10 %) in storage at 50 days. Total structural sugar levels of the stored material were preserved, although glucan enrichment and xylan loss were documented in the high and intermediate flow conditions. By understanding the role of oxygen availability on biomass storage performance, the requirements for high moisture storage solutions may begin to be experimentally defined.

순환식 암모니아 반응기(Ammonia Circulation Reactor (ACR))를 이용한 옥수수대의 전처리 및 효소 당화율 향상

목질계 바이오매스인 옥수수대 전처리를 위하여 고안된 순환식 암모니아 전처리 반응기(Ammonia Circulation Reactor (ACR))를 이용하여 연구하였다. 이 전처리 방법은 적은 양의 액체를 사용하도록 고안되었으며 이 연구에선 기존의 전처리 공정보다 낮은 전처리 온도(<TEX>$60{\sim}80^{\circ}C$</TEX>), 반응시간(4~12 hour) 그리고 고체:액체 비율(1:3~1:8) 등의 공정 조건을 실험 하여 효과를 비교하였다. 즉 여러 공정 조건에서 전처리 후 고형물의 잔류 고체량, 당, Lignin 함량, 그리고 효소당 화율 등을 측정하였다. 여러 실험 조건에서 공통적으로 관찰된 것은 전처리 조건이 더 가혹해 지면 Lignin의 제거율이 가장 큰 영향을 받았으며, 47.6~70.6% 범위로 나타났다. 반면 다른 당(Glucan, Xylan)은 손실이 비교적 작게 나타났다. 모든 실험 조건에서, 전처리된 고형물의 Glucan 손실율은 4.7~15.2% 범위로 변화가 크지 않았으며 Xylan 손실율은 여러 조건의 변화에 따라 7.4~25.8% 정도 범위로 나타났다. 암모니아 순환 전처리로 8~12 hour 동안 처리된 옥수수대는 90.1~94.5%의 높은 72-h Glucan 당화율을 (15 FPU-GC220+30 CBU)/g-glucan의 효소 투입으로 나타냈으며 순수 Cellulose인 Avicel의 당화율(92.7%)과 비슷하거나 높았다. 또한 8~12 hour 처리된 옥수수대의 초기 24-h Glucan 당화속도는 73.0~79.4%로 Avicel의 같은 시간 당화율인 69.5% 보다 높게 나타났다. 반응시간을 증가는 보다 많은 Lignin을 제거하였으며 따라서 효소 당화율 증가에 기인한 것으로 보인다. Ammonia circulation reactor (ACR) was devised for the effective pretreatment of corn stover. This method is designed to circulate aqueous ammonia continuously so that it can reduce the chemical and water consumption during pretreatment. In this study, ammonia pretreatment with various reaction conditions such as reaction time (4~12 hour), temperature (<TEX>$60{\sim}80^{\circ}C$</TEX>), and solid:liquid ratio (1:3~1:8) was tested. Chemical compositions including solid remaining after reaction, lignin and carbohydrates were analyzed and enzymatic digestibility was also measured. It was observed that as reaction conditions become more severe, lignin removal was significantly affected, which was in the range of 47.6~70.6%. On the other hands, glucan and xylan losses were not substantial as compared to that of lignin. At all tested conditions, the glucan loss was not changed substantially, which was between 4.7% and 15.2%, while the xylan loss varied, which was between 7.4% and 25.8%. With (15 FPU-GC220+30 CBU)/g-glucan of enzyme loading, corn stover treated using ammonia circulation reactor for 8~12 hours resulted in 90.1~94.5% of 72-h glucan digestibility, which was higher than 92.7% of <TEX>$Avicel^{(R)}$</TEX>-101. In addition, initial hydrolysis rate (at 24 hour) of this treated corn stover was 73.0~79.4%, which was shown to be much faster than 69.5% of <TEX>$Avicel^{(R)}$</TEX>-101. As reaction time increased, more lignin removal and it was assumed that the enhanced enzymatic digestibility of treated biomass was attributed to the lignin removal.

Effect of dimethyl sulfoxide on ionic liquid 1-ethyl-3-methylimidazolium acetate pretreatment of eucalyptus wood for enzymatic hydrolysis

Ground eucalyptus wood was pretreated with 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc)-dimethyl sulfoxide (DMSO) solutions with different mixing ratios under various conditions. The changes in the composition and structure of the biomass were investigated; and the enzymatic hydrolysis performance of the pretreated biomass was evaluated. [EMIM]OAc-DMSO pretreatment had a relatively mild effect on the composition of the biomass, but excessively high pretreatment temperatures led to massive loss of xylan after pretreatment. The enzymatic digestibility of the biomass was significantly improved with increased pretreatment temperature. X-ray diffraction analysis revealed that the disruption of cellulose crystal structure by [EMIM]OAc at a sufficiently high temperature was primarily responsible for the remarkable improvement in the digestibility. Appropriate addition of DMSO could help minimize the consumption of [EMIM]OAc without impairing the performance of the ionic liquid, and contribute to the improvement in pretreatment efficiency due to the viscosity reduction effect on the pretreatment liquor.

IRX14 and IRX14-LIKE, Two Glycosyl Transferases Involved in Glucuronoxylan Biosynthesis and Drought Tolerance in Arabidopsis

IRX14 and IRX14-LIKE (IRX14L) are two closely related glycosyl transferases in the glycosyl transferase 43 (GT43) family of Arabidopsis. A T-DNA insertion mutant for IRX14 results in comparatively minor changes, such as irregular xylem, while a mutation for IRX14L results in no changes. However, an irx14 and irx14L double mutant severely affects growth and development, with the dwarf plants failing to produce an inflorescence stem. Plants that are homozygous for IRX14 but heterozygous for IRX14L (irx14 irx14L(±)) exhibit an intermediate phenotype, including noticeably smaller leaves, stems, and underdeveloped siliques. Additionally, the T-DNA insertion mutant for IRX14 was found to result in a drought-tolerant phenotype. Carbohydrate analysis of total cell wall extracts revealed a reduction in xylose for the irx14 and irx14 irx14L(±) mutants, consistent with a defect in glucuronoxylan biosynthesis. Immunolocalization of xylan with the LM10 antibody revealed a loss of xylan in irx14 mutants and a further reduction in the irx14 irx14L(±) mutants. IRX14L likely functions redundantly with IRX14 in glucuronoxylan biosynthesis, with IRX14 having a more important role in the process.

Fungal treatment of cornstalks enhances the delignification and xylan loss during mild alkaline pretreatment and enzymatic digestibility of glucan

Fungal treatment with Irpex lacteus was used to enhance the delignification and xylan loss during mild alkaline pretreatment and subsequent enzymatic conversion in this research. The 15-day bio-treatment can modify the lignin structure and increase losses of lignin (from 75.67% to 80.00%) and xylan (from 40.68% to 51.37%) during alkaline pretreatment, making the enzymatic conversion more efficient. The high digestibility of glucan can be obtained after the bio-treatment and alkaline pretreatment at near room-temperature (30°C), and the maximum digestibility increased 14% in comparison with that after the sole alkaline pretreatment. The bio-treatment enhanced delignification and glucan digestibility more significantly when the alkaline pretreatment was performed at lower severity. Additionally, Nuclei Growth model with a time-dependent rate constant can describe well the delignification and xylan loss. Results indicated that the bio-treatment increased the rate constant of initial reaction, but accelerated the decline of rate constant during alkaline pretreatment.

Characterisation of the heterogeneous alkaline pulping kinetics of hemp woody core

A model was developed, based on the power law of growth and Avrami’s concepts in nuclei growth to describe the heterogeneous nature of alkaline pulping kinetics, taking into account the effects of effective alkali concentration and temperature. It was then applied against published data to estimate model parameters. The final form of the model applied to alkaline pulping of thin hemp woody core in flow-through reactors could be represented by a first order rate equation with a time-dependent rate constant: - d Y d t = A ∗ OH - b ∗ exp - E RT n ∗ Y ∗ t n - 1 . The rate equations applied for delignification, cellulose and xylan losses. It was found that the heterogeneous kinetic models predicted well the delignification and xylan loss of hemp woody core, with R 2 values of 0.96 and 0.97, respectively. The model was, however, less accurate in predicting cellulose loss. The values n, which could represent the acceleration/deceleration extent of growth of reacting volumes, were found to be less than unity. This demonstrated the heterogeneous characteristics of alkaline pulping for hemp woody core.

Kinetics of polysaccharide degradation during ethanol–alkali delignification of giant reed—Part 1. Cellulose and xylan

The degradation kinetics of the principal polysaccharides (cellulose and xylan) of the agro-fibre crop Arundo donax L. (giant reed) during ethanol–alkali delignification is reported. Based on the properties of a multi-component reaction system, the degradation kinetics of both polysaccharides was accurately described in terms of two simultaneous irreversible first-order reactions corresponding to removal of two kinetically homogeneous fractions. The moderate cellulose losses during pulping (about 4.5%) result mainly from the removal of the more reactive cellulose fraction, that accounted for 4% of initial cellulose. The bulk of the cellulose (96%) degrades slowly with three orders lower rate with pulping progress. The apparent activation energy of cellulose fractions degradation was estimated as 105.2 and 106.5 kJ mol −1, respectively. Substantial loss of xylan during pulping (about 55%, as a homoxylan) is caused by fast removal of the first very reactive fraction, covering about 48% of total xylan. The degradation rate of the second xylan fraction is only one order higher of the bulk cellulose degradation. The activation energy of xylan fractions degradation was found as 74.4 and 140.9 kJ mol −1, respectively.

Hydrothermal and pulp processing of Eucalyptus.

Hydrothermal processing of Eucalyptus wood was performed at operation temperature of 181 degrees C, processing time or 37.5 min and solid water ratio of 1/6 to ensure a maximum loss of xylan recuperation with minimum cellulose fibre degradation. Under those conditions, the loss of xylan was 22% less than that achieved with the conditions 196 degrees C, 50.6 min and 1/8 (solid/water). IN In addition, an experimental design was used to study the influence of process variables: temperature (145-175 degrees C), pulping time (40-120 min) and ethanol concentration (40-70% weight concentration), on the properties of pulps (yield, kappa number, viscosity, cellulose, xylan, lignin acetyl groups contents and brightness) and paper sheets (stretch index, burst index and tear index) obtained from the solid fraction after hydrothermal treatment of Eucalyptus globulus. Pulps with acceptably high physical and chemical properties can be obtained operating at 175 degrees C for 90 min with 55% ethanol concentration.

Characterization and fermentation of steam exploded cotton gin waste

Cotton gin waste was collected from a cotton ginning plant in Virginia and characterized before and after steam explosion to evaluate its potential applications for higher value products such as ethanol. The raw cotton gin waste had high levels of ash ( 10.5 wt% ) and acid insoluble material ( 28.8 wt% ). The xylan and cellulose contents were, respectively, 9 and 37 wt% . The cotton gin waste was steam exploded in a batch gun at severities ranging from 2 to 4.9. Substantial solubilization/degradation of fiber material (9– 17 wt% ) occurred during steam explosion pretreatment especially at the high severities. Mannan, galactan, and arabinan were completely solubilized/degraded at severities greater than 3.56. Both glucan and xylan were solubilized/degraded at all severities, but xylan loss was considerably higher. The steam exploded material was essentially cellulose and acid insoluble material and small fractions of xylan at severities greater than 3.56. Steam explosion improved the enzyme hydrolysis of the material from 42% to 67% during 24 h incubation. E. coli KO11 was effective in converting the enzyme hydrolyzed substrate to ethanol. The highest ethanol yield (83% of theoretical yield) was achieved for material treated at a severity of 3.56. Both xylose and glucose were fermented to ethanol by the microorganism.

COMPARISON OF CHARACTERISTICS OF SOFTWOOD AND HARDWOOD SULPHITE PULPS DURING THE BLEACHING PROCESS

Softwoods (spruce+fir, and fir only) and hardwoods (mixed hardwood, and birch only) unbleached sulphite paper grade pulps were bleached with three-stage processes (chlorination, caustic extraction, hypochlorite) and a comparison was made on behavious of softwood and hardwood sulphite pulps during the bleaching.1) In comparison with softwood unbleached sulphite of the same Sieber number, hardwood sulphite pulps were lower in the bleaching loss (Fig. 1), and higher in brightness of bleached pulp (Table 1 and 2) and consumption of caustic soda (Fig. 2). The yields of boths oftwood and hardwood bleached pulps were lower than those expected from their lignin contents calculated from Sieber number of unbleached pulps.2) The loss of xylan and mannan in pulps during bleaching process were very small and total amounts of them were about 0.2% in both softwood and hardwood unbleached pulps (Sieber number about 52) (Table 5). The dissolved carbohydrate materials were mainly xylan in the case of hardwood pulp, while considerable amount of mannan was found in addition to xylan in the case of softwood pulp. Considerable amounts of uronic acids were also removed during these treatments and the loss mounted to 20-30% of original uronic acid contents of both softwood and hardwood unbleached sulphite pulps (Table 3 and 4).3) Lignin contents of unbleached pulps were determined UV-absorptiometrically on phosphoric acid solution. It was shown that the lignin content of the herdwood unbleached sulphite pulps was about 20% less than that of softwood unbleached sulphite pulps of the same Sieber number (Fig. 5 and 6). It seems that the difference in the yield of softwood and hardwood bleached sulphite pulps was mainly due to the difference in the lignin contents.4) The amounts of lignin eliminated from unbleched sulphite pulps were determined UV-absorp-tiometrically in the bleaching process. Lignin in unbleached hardwood sulphite pulp was easier to remove than that of softwood pulp during caustic extraction after chlorination (Fig. 8) and hypochlorite bleaching. Considerable amount (about 35%) of the former was also removed even by 1% NaOH extraction at 20°C for 1 hr. (Fig. 9)