Cellulose Fermentation: Effect of Substrate Pretreatment on Microbial Growth

The effects of chemical, physical, and enzymatic treatments of rice straw and sugarcane bagasse on the microbial digestibility of cellulose have been investigated. Treatment with 4% NaOH for 15 min at 100 C increased the digestibility of cellulose from 29.4 to 73%. Treatment with 5.2% NH₃ could increase digestibility to 57.0% Treatments with sulfuric acid and crude cellulase preparation solubilized cellulose but did not increase the digestibility. Grinding or high-pressure cooking of the substrate had little effect on increasing the digestibility of cellulosic substrates by the Cellulomonas species.     

Semisolid fermentation of ryegrass straw

Candida utilis, Aureobasidium pullulans, and Trichoderma viride were grown on pretreated ryegrass straw. The pretreatment consisted of hydrolysis of straw with 0.5 N H₂SO₄ (water-substrate, 3:1) at 121 C, 100 C, and room temperature and adjustment of the hydrolysate to pH 4.5 to 5.0 with 5 N NH₄OH. The 121 C pretreatment yielded a material containing 30% sugar and 2.3% N. The fermentation was carried on semisolid substrate (moisture level, 75%) in rotating jars for 2 to 3 days at room temperature. The organisms grew rapidly during the period from 18 to 42 h of incubation. During this period the number of microbial cells increased by 20- to 200-fold, and the level of NH₃-N decreased from 1.3 to 0.9%. The fermentation resulted in a fourfold increase in protein, fivefold increase in crude fat, and 40% increase in the digestibility of straw. The best result in terms of increasing protein and digestibility of straw was obtained when C. utilis was grown on straw preheated at 121 C.     

New crop residues and forages for Western Canada: Assessment of feeding value in vitro and response to ammonia treatment

A survey was conducted on the feed value for ruminants of a variety of crop residues and forages, with particular emphasis on crop residues and forages not currently grown extensively in Western Canada. Crop residues with feed values significantly higher than wheat (Triticum aestivum L.) or barley (Hordeum vulgare L.) straw were investigated, and the response to ammonia treatment was evaluated, to determine which materials could be appreciably improved in feed value by this technique. Some of the crop residues evaluated by digestibility in vitro and crude-protein content had a significantly higher feed value, without chemical processing, than the cereal straws often given to cattle in Western Canada. Ammonia treatment improved both the organic matter digestibility in vitro and crude-protein content of some residues significantly, while other materials showed only an improvement in crude protein. The organic matter digestibility in vitro of sunflower (Helianthus annus L.) crop residue and Jerusalem-artichoke (Helianthus tuberosis L.) forage and residue was initially higher than that of alfalfa (Medicago sativa L.) or sweet clover [Melilotus officinalus (L.) Lam] and did not increase appreciably with ammonia treatment. Faba-bean (Vicia faba L.) residue was only slightly inferior to these materials and showed a moderate improvement after treatment with ammonia. Untreated bullrush-millet [Pennisetum americanum (L.) Schum] whole-crop forage was equivalent to alfalfa and sweet clover in digestibility in vitro and responded quite well to ammonia treatment. Kochia (Kochia scoparia Shrad) forage had a relatively high digestibility in vitro and crude-protein content when harvested at the flowering stage. Mature kochia had a digestibility in vitro equivalent to barley straw and did not respond well to ammonia treatment.     

Fermentation characteristics and feeding value of ensiled poultry litter containing wheat straw,bagasse or sawdust

Poultry excreta substantially increased the crude protein (CP) content and the calcium and phosporus content of the base bedding materials. The crude fibre (CF) content of sawdust (52.3%) was higher than that of wheat straw (38.9%) and bagasse (30.2%). Dry matter digestibility in vitro (IVDMD) of wheat straw, bagasse and sawdust poultry litters (PL) was 65.4, 64.5 and 48.1%, respectively. Green sorghum fodder when ensiled alone or with 20% wheat straw PL, sawdust PL or bagasse PL on fresh basis contained 4.67, 7.80, 10.00 and 7.55% CP, respectively. Nitrogen-free extract (NFE) content of PL silages was lower than that of the control. Apart from wheat straw PL, all silages accumulated considerable amounts of lactic acid. The total volatile fatty acids (TVFA) concentrations were similar for all silages. The addition of PL caused an increase in the proportion of ammonia nitrogen. A feeding trial with crossbred adult male cattle revealed no significant difference in dry matter (DM), CP and ether extract (EE) digestibility of wheat straw and bagasse PL silages. The CF digestibility was similar for all the silages. Sawdust PL silage, however, was significantly lower (P < 0.05) in digestibility of DM, EE and NFE compared to other PL based silages. The DCP and TDN values for the control, wheat straw, bagasse and sawdust PL silages were 2.0, 60.1; 4.3, 45.3; 6.1, 50.3 and 2.9, 41.9 kg/100 kg DM, respectively.     

Ammoniation of wheat straw and native grass hay during baling of large round bales

Wheat straw and native grass hay were treated with anhydrous ammonia during baling with a large round baler. In Experiment 1, ammonia (3.2 and 7.1% w/w of straw DM) was applied by use of a Cold-flow Converter to wheat straw that either had not been sprayed or had been sprayed with one of two rates of water as it passed over the pick-up frame of the baler. Straw water concentrations immediately after baling were 13.8 and 23.8%, respectively, for the low and high rates of water application. Straw water concentrations were about 12 percentage units lower than anticipated, and indicate that water penetration of the hard cuticular surface of the straw was low. Treatment with 3.2% ammonia of straw not sprayed with water increased the crude protein content from 3.2 to 5.7% immediately after baling. However, none of the ammonia-nitrogen (NH₃-N) was retained 45 days after baling, and dry matter digestibility in vitro (IVDMD) of the straw was not increased. Straw that was treated with low levels of both ammonia and water contained 6.0% crude protein after storage, and IVDMD increased 27% (i.e., 36.7 vs. 28.9%; P < 0.001). Retention of NH₃-N after storage ranged from ?1.4 (low level of ammonia and no added water) to 14.8% (low level of both ammonia and water) and was increased (P < 0.001) by added water at the low level of ammonia application.The effects of crimping wheat straw during baling and addition of a surfactant (0.2% v/v) to aqua-ammonia on crude protein content, retention of NH₃-N and the IVDMD of straw were studied in Experiment 2. Water content of ammoniated straw in Experiment 2 (ca.14%) was similar to that of straw sprayed with the low level of water in Experiment 1. Crimping did not visibly disrupt the surface of the straw, nor affect crude protein content or IVDMD. Addition of surfactant to the aqua-ammonia increased (P < 0.01) the crude protein content after storage of non-crimped and crimped straw, respectively, by 0.3 and 1.5 percentage units (P < 0.05 for crimping by surfactant interaction). Straw IVDMD was not increased by either crimping or addition of surfactant to the aqua-ammonia. Retention of NH₃-N after storage, which ranged from 26 to 49%, was greater than that of Experiment 1, and was attributed to the lower level of ammonia application (1.7% of straw DM). Native grass hay readily adsorbed aqua-ammonia. Water content of the hay was increased from 12.2 to 28.7%, and the crude protein content was increased from 4.4 to 13.9% by ammoniation. The studies indicate that while ammoniation of crop residues during the baling operation is a possible means of treatment, low retention of NH₃-N remains a problem. Disruption of the hard cuticular surface of residues such as wheat straw may improve penetration of aqua-ammonia and therefore the effectiveness of treatment.     

Different sources of ammonia for improving the nutritive value of low quality roughages

The study was undertaken to investigate the effectiveness of anhydrous NH₃, aqueous NH₄OH and urea + urease as sources of ammonia for treating maize stover, rice and wheat straws at graded treatment rates of 0, 25 and 50 g NH₃/kg DM of roughage and at two moisture levels of 20 and 40% in all combinations in improving dry matter digestibility in vitro (IVDMD), organic matter digestibility in vitro (IVOMD) and crude protein (CP) contents when allowed to react for 15 or 30 days.Rate of ammonia was the most important factor in enhancing IVDMD, IVOMD and CP. Moisture level and days of reaction had a less important influence on the parameters measured. While anhydrous NH₃ was most effective in improving IVDMD and IVOMD of maize stover, aqueous NH₄OH had a similar effect in increasing IVDMD and IVOMD of rice and wheat straws and urea + urease was the least effective but promising. Highest responses in IVDMD and IVOMD were obtained with rice straw, followed by wheat straw and, lastly, maize stover.In a second experiment maize stover which was treated with aqueous NH₄OH at 0, 25 and 50 g NH₃/kg DM at two moisture levels of 20 and 40% was given to Black Headed Persian rams. Digestibility of DM and OM and voluntary feed intake were improved significantly (P < 0.01) by ammonia treatment and there was also a significant (P < 0.01) response to increasing moisture levels.     

Digestibility of diets containing increasing levels of NaOH-treated or untreated wheat straw

Sodium hydroxide-treated or untreated wheat straw was included in a basal alfalfamaize diet at 0, 10, 20 and 40%. As the level of straw increased, the apparent digestibility of dry matter (DM) and organic matter (OM) by sheep, decreased linearly (P < 0.01), with a faster decrease (P < 0.05) for diets containing untreated straw. The digestibility of DM decreased by 0.22 and 0.41% and OM by 0.24 and 0.42% for treated and untreated straw diets, respectively, with each 1% increase of straw in the diets.Addition of treated straw increased (P < 0.05) digestibility of cell wall constituents (CWC), acid detergent fibre (ADF) and hemicellulose (HC). However, when untreated straw was added, the digestibility of HC was reduced, whereas the digestibility of CWC and ADF was dependent on the level of straw added. Increasing levels of NaOH-treated straw in the diets produced linear increases (P < 0.05) in digestibility of CWC, ADF and HC. However, significant (P < 0.05) linear or quadratic responses were not noted in the digestibility of CWC, ADF and HC with increasing levels of untreated straw in the diet. Apparent digestibility of crude protein was not affected by addition of either NaOH-treated or untreated straw to the diet.In general, although changes in nutrient digestibility of the basal component small, large changes in the digestibility of nutrients in the straw component were apparent and accounted for the major differences in digestibility of the diets. The absence of curvilinearity in the regression equations suggested that there were no associative effects.     

Alkali treatment and fermentation of straw for animal feed

The feed value of annual ryegrass straw was improved by treatment with various concentrations of NaOH or NH₃ followed by fermentation of the treated straw with a mixed culture of Cellulomonas sp. and Alcaligenes faecalis. Laboratory feeding trials with voles showed that NaOH or NH₃ treatment considerably increased the feed efficiency of straw, but apparently gave a poorly palatable product. Fermentation tended to decrease the in vitro rumen digestibility (IVRD) of alkali-treated straw. The fermentations were carried out aerobically on a semisolid straw matrix having 11–86% moisture. Treatment by both NaOH and NH₃ increased the IVRD of straw. NH₃ also increased the nitrogen content in straw. The optimum condition for alkaline treatment of the straw was 4–6% NaOH for 1 hr or with 3% NH₃ for four weeks at room temperature. A minimum of 63% moisture was needed for significant fermentation of the straw. The combined effects of NaOH treatment and fermentation more than doubled crude protein, doubled crude fat, and increased IVRD by 75%. The NH₃ plus fermentation treatment tripled crude protein, doubled crude fat, and increased IVRD by 60%. Acetic acid was the main volatile fatty acid in the fermented straw.     

The feeding value of ammoniated flax straw,wheat straw and wheat chaff for beef cattle

Two experiments were conducted to assess the feeding value of ammoniated and untreated flax straw, wheat straw and wheat chaff in comparison to a mixed bromegrass/alfalfa hay. Anhydrous ammonia was applied to the crop residues at the rate of 35 kg t⁻¹ dry matter. In the first experiment, the effect of ammoniation on crude protein, acid detergent fibre (ADF), neutral detergent fibre (NDF) and acid detergent lignin (ADL), digestible organic matter in vitro and in vivo (DOM%), ADF and NDF digestibility of the crop residues was determined. In the second experiment, ammoniated flax straw, ammoniated wheat straw, ammoniated and untreated wheat chaff, each supplemented with barley, were compared to bromegrass/alfalfa hay as feed sources for wintering beef cows.Ammoniation increased the crude protein content of the crop residues ∼2-fold. Wheat straw DOM in vitro and in vivo was not increased by ammoniation. Ammoniation increased the DOM in vitro of wheat chaff from 36.3 to 46% and flax straw from 35.2 to 46.3%. The DOM in vivo increased from 53.3 to 63.4% (P < 0.05) for wheat chaff and from 33.9 to 58.4% (P < 0.05) for flax straw following ammoniation. Digestibility of ADF increased from 9.9 to 43.9% (P < 0.05) and of NDF from −0.6 to 37.9% (P < 0.05) in flax straw with ammoniation. Non-significant increases in ADF and NDF digestibility were observed for all other crop residues. Lignin content was not changed in the crop residues by ammoniation.In the winter feeding trial, young cows gained more weight than older cows (P < 0.05). Average daily gains of cows were greatest for hay followed by ammoniated flax straw, ammoniated chaff, untreated chaff and ammoniated wheat straw rations (P < 0.05). Increases in backfat in the younger cows was greatest with hay and ammoniated flax straw, followed by ammoniated chaff and ammoniated wheat straw (P < 0.05). Untreated chaff caused no increase in backfat thickness.Ammoniated flax straw (3.2 kg day⁻¹) given with barley (5.6 kg day⁻¹), is similar in feeding value to medium quality bromegrass/alfalfa hay. Furthermore, wheat chaff and ammoniated wheat chaff show good potential as alternatives to hay in winter feeding.     

Microbial biomass production from rice straw by fermentation with Penicillium janthinellum

Production of microbial biomass through fermentation of pretreated rice straw using Penicillium janthinellum (St-F-3B) is reported, with emphasis on the use of non-effluent generating pretreatment procedures. The fungus readily metabolized a rice straw substrate that had been subjected to alkali pretreatment by steaming at atmospheric pressure followed by the neutralization of the alkali. The crude protein content of the microbial biomass averaged 15–20%. The fermentation could be carried out in aerated-agitated fermenters using fertilizer grade nutrient salts to produce a biomass with 17.5% crude protein. When operated on a semicontinuous basis using 20% of the previous batch as inoculum, successive batches produced a biomass product with 12–19% crude protein content in 48 h. The problems of developing a technology for protein from agricultural residues with particular reference to developing countries are discussed.     

Effect on digestibility and nitrogen content of barley straw of different ammonia treatments

The article discusses the effect on solubility in cellulolytic enzyme suspensions, digestibility in vitro and crude protein content (F × 6.25) of treating barley straw with various dosages of NH₃ (2.6–5.9%), at various temperatures (15–75°C) for various treatment times (1–14 days).An increase in any of the above factors resulted in an increased intensity of treatment, with an increase in temperature of 15°C being equal to an increased NH₃-dosage level of 1.5% or prolongation of the treatment time by a factor of 4.5Digestibility in vitro increased with increased intensity of treatment, until a maximum level was obtained. Beyond this point, an increase in NH₃-dosage, or especially in temperature, tended to decrease digestibility in vitro. Maximum digestibility could be obtained, for example, with 2.6% NH₃, 62°C and 4 days incubation, or 5.9% NH₃, 30°C and 3–7 days incubation.Likewise, both solubility in cellulolytic enzyme suspensions and crude protein content increased with increased intensity of treatment, up to a certain level. Thereafter, increased dosing with NH₃, higher temperatures or longer incubation times had little or no effect. However, maximum values were obtained with a greater intensity of treatment than the maximum digestibility in vitro, and no tendency towards decreased values was observed.Increased enzyme solubility, beyond that corresponding to maximum digestibility in vitro, was accompanied by an increased rate of fermentation and a decreased content of neutral detergent fibre.Treatment with heat (100°C) and pressure after incubation, to simulate pelleting before evaporation of surplus NH₃, was also investigated. Only after the lowest incubation temperatures, however, was there an obvious tendency towards increased digestibility. The enzyme solubility was, on the other hand, very obviously increased. Crude protein content was also slightly increased by the heat- and pressure-treatment.     

Improvement of the bioconversion and biotransformation efficiencies of the oyster mushroom (Pleurotus sajor-caju) by supplementation of its rice straw substrate with oil seed cakes

Supplementing the rice straw substrate colonized by the mushroom, Pleurotus sajor-caju, with powdered oil seed cakes (mustard, niger, sunflower, cotton, and soyabean) increased the mushroom yields between 50 and 100%, compared to the unsupplemented substrate. Oil seed cake supplementation also effected an increase in the solubility of the rice straw substrate; there was an increase in the contents of free sugars and amino acids, and a decrease in cellulo-hemicellulosics. Correspondingly, there was also an increase in the activities of carboxymethylcellulase, hemicellulase, and protease. In vitro dry matter enzymatic digestibility measured by two-step enzymatic digestibility of the spent straw (material remaining from the straw substrate, supplemented with the oil seed cakes), indicated a significant increase over that of the spent straw derived from the unsupplemented lot.     

Biodegradation of wheat straw lignocarbohydrate complexes (LCC)

Summary In laboratory and semi-industrial scale experiments the influence of the substrate water content, temperature, and incubation time on the progress of solid state fermentation of straw colonized by white rot fungi was investigated. The parameters used to evaluate the fermentation process were degradation of total organic matter and lignin, in vitro digestibility, the content of water soluble substances in the substrate and the pH.The degradation of total organic matter was species specific. Only Trametes hirsuta enhanced the degradation at elevated temperature (30 °C). With Abortiporus biennis, Ganoderma applanatum, and Pleurotus serotinus, elevated temperature had and adverse effect. Prolonged incubation only improved degradation of straw by the relatively slowgrowing fungi Ganoderma applanatum, Lenzites betulina, and Pleurotus sajor caju.Elevated temperature and prolonged incubation shifted the relative degradation rates in favour of total organic matter degradation. With Ganoderma applanatum, Pleurotus ostreatus, and Pleurotus serotinus lignin degradation, even on an absolute scale, was less at 30 °C than at 22 °C.In general, the in vitro digestibility also decreased, when the incubation time and temperature were raised. With Ganoderma applanatum the in vitro digestibility dropped below the value of the sterile straw control.Solid state fermentation of straw was at an optimum at a medium water content of 75 ml/25 g of substrate. However, most of the fungi tested could digest straw over a wide range of water content. At higher water contents (125–150 ml/25 g of substrate) an increased production of aerial mycelium was observed.In semi-industrial batch experiments (40 kg) with Abortiporus biennis the in vitro digestibility dropped below the reference value for sterile straw during the first 19 days of incubation. Later, the in vitro digestibility again rose and reached its optimum after about 60 days. The in vitro digestibility in the semi-industrial experiments was always lower than in the laboratory experiments (+9% and +25%, respectively).In long term experiments (2.5 kg batches, 8 months of incubation) very different values for the in vitro digestibility were found, and these depended on the fungus used (Abortiporus biennis, +16%; Pleurotus ostreatus, +4%; and Ganoderma applanatum, –27%).     

The effect of white-rot basidiomycetes on chemical composition andin Vitro digestibility of wheat straw

Five white-rot basidiomycetes were evaluated for their potential to improve ruminal degradation of wheat straw.Polyorus brumalis, Lyophyllum ulmarium III,Trametes gibbosa, Pleurotus ostreatus, and aPleurotus ostreatus mutant were incubated on wheat straw for 30 d at 28°C. Detergent fiber, crude protein andin vitro dry matter digestibility (IVDMD) were determined. The results showed increasing crude protein and ash contents in fungus-treated straw. IVDMD values were increased in straws treated withP. ostreatus, P. ostreatus mutant andT. gibbosa only. Relative to untreated wheat straw the detergent fiber content—neutral detergent fiber (NDF), and acid detergent fiber (ADF) was reduced in fungus-treated straw and out of three fractions—hemicellulose, cellulose and lignin, hemicellulose showed the largest proportionate loss whereas lignin the smallest one in all 5 samples of fungus treated straw.     

The effect of ammoniation on the intake and nutritive value of straw

Studies were conducted to compare the increases in dry matter digestibility (DMD) in vitro and in vivo and to determine the metabolisable energy (ME) value of straw ammoniated at ambient temperature. Two stacks of straw sealed with polyethylene were allowed to react with 3% (w/w) anhydrous NH₃ for 30 and 56 days, respectively. Both DMD in vitro and nitrogen tests were carried out over an eight-week period subsequent to opening the stacks. Digestibility in vivo was measured with 12 wether lambs. The non-treated and ammoniated straws were given ad libitum, with a supplement of either ground barley or a lamb concentrate which contained 16% crude protein (CP).There was a mean increase of 15 percentage units in DMD in vitro for the ammoniated straw irrespective of whether it was treated for 30 or 56 days. The corresponding increase in mean DMD in vivo was 14.2 units. The CP content of the straw was increased from 3.1 to 7.6%. The increase in DMD in vitro and total N content was maintained throughout the sampling period. Approximately 58% of the anhydrous NH₃ added to the straw appeared to have been irreversibly “bound” to the straw. The ME values for the ammoniated straw were 6.78 and 7.49 MJ/kg when the straw was supplemented with either barley or the lamb concentrate, respectively. Straw ammoniation had a marked effect on intake. The overall increase in intake was 70% for the treated compared with the non-treated material.     

Arrowroot (Maranta arundinacea), food,feed, fuel,and fiber resource

Arrowroot biomass and processing residues were evaluated as as a feed, fuel and fiber resource. Ensiled aerial biomass and coarse and fine arrowroot processing residues contained 10.8–21.1% crude protein; 11.1–30.2% crude fiber; 3.8–17.0% ash; and an in vitro dry matter digestibility of 38.5–60.3%. Theoretical yields of 0.27 and 1.60 l of methane at standard temperature and pressure per liter of rhizome wash water and starch-settling water were calculated, respectively. Fuel alcohol production potential from yeast-supplemented aerial biomass and coarse residue were identified. Laboratory pulping of coarse residue was performed. The coarse residue has qualities that may be suited to tear-resistant specialty grade papers, such as wrapping paper and bags. The utilization of arrowroot by-products may lead to increased cultivation of this species as a food, feed, fuel and fiber resource. By-product utilization will also reduce environmental pollution presently resulting from direct discharge of unused by-products.     

Effects of Phytoecdysteroids (PEDS) Extracted from Cyanotis arachnoidea on Rumen Fermentation,Enzyme Activity and Microbial Efficiency in a Continuous-Culture System

The objective of this study was to evaluate the effects of supplementation of phytoecdysteroids (PEDS) extracted from Cyanotis arachnoidea on rumen fermentation, enzymes activity and microbial efficiency in a dual flow continuous-culture system. A single-factor experimental design was used with twelve fermenters in 4 groups with 3 replicates each. Fermenters were incubated for a total of 7 days that included first 4 days for adaptation and last 3 days for sampling. PEDS was added at levels of zero (as control), 5, 10, and 15 mg/g of the substrate (DM). The results showed that increasing supplementation levels of PEDS resulted in incremental digestibility of dry matter (DMD) (quadratic, P = 0.001) and organic matter (OMD) (quadratic, P = 0.031), but unchanged digestibility of neutral detergent fiber (NDFD), crude protein (CPD) and acid detergent acid (ADFD). As supplementation levels of PEDS increased, there were decreased response in the concentration of ammonia nitrogen (NH₃-N) (linear, P = 0.015) and increased response in molar proportions of butyrate (linear, P = 0.004), but unchanged response in total volatile fatty acid (TVFA) and the molar proportion of acetate and propionate, respectively. Increasing PEDS supplementation levels decreased the ratio of acetate to propionate (linear, P = 0.038), suggesting an alteration of rumen fermentation pattern occurring due to PEDS supplementation in the diet. Supplementation of PEDS significantly increased activities of glutamate dehydrogenase (quadratic, P = 0.001), alanine dehydrogenase (quadratic, P = 0.004), glutamate synthase (linear, P = 0.038), glutamine synthetase (quadratic, P = 0.011), respectively. There were no discernible differences in the activity of carboxymethyl cellulose (CMCase), xylanase and protease regardless of the treatments. The daily production of microbial nitrogen (linear, P = 0.002) and microbial efficiency (MOEEF) (linear, P = 0.001) increased linearly as supplementation levels of PEDS increased. The decreased response of fluid NH₃-N and the increased response of MN indicated that PEDS positively increased the synthesis of microbial proteins.     

Effect of different supplements on bioprocessing of wheat straw by Phlebia brevispora: changes in its chemical composition, in vitro digestibility and nutritional properties

Bioprocessing of wheat straw was carried out by Phlebia brevispora under solid state conditions. Effect of different supplements on lignocellulolytic enzymes production, degradation of straw cell wall fibers and its resultant effect on nutritional quality of wheat straw were studied. Ammonium chloride and malt extract were more effective in terms of ligninolysis and enhanced in vitro digestibility. The concentration of the selected supplements and the moisture content was worked out using response surface methodology in order to minimize the loss in total organic matter so as to selectively degrade lignin. The experiment was scaled up to batches of 200 g under optimized conditions and the degraded substrate was analyzed for its biochemical properties. P. brevispora degraded 290 g/kg of lignin and enhanced the in vitro digestibility from 150 to 268 g/kg (78%). Crude protein, amino acids, total phenolic contents and antioxidant properties were significantly higher in degraded straw.     

Delignification of Wheat Straw by Pleurotus spp. under Mushroom-Growing Conditions

Pleurotus sajor-caju, P. sapidus, P. cornucopiae, and P. ostreatus mushrooms were produced on unsupplemented wheat straw. The yield of mushrooms averaged 3.6% (dry-weight basis), with an average 18% straw weight loss. Lignin losses (average, 11%) were lower than cellulose (20%) and hemicellulose (50%) losses. The cellulase digestibility of the residual straw after mushroom harvest was generally lower than that of the original straw. It does not appear feasible to simultaneously produce Pleurotus mushrooms and a highly delignified residue from wheat straw.     

Effect of refiner defibrizing on the fermentability of ryegrass straw

The effects of two grinding methods, hammer milling and defibrizing by disk refining, on the fermentability of ryegrass straw were investigated. Disk refined or defibrized straw produced more sugar than hammer milled straw. Release of sugar was especially pronounced when H₂SO₄ was added to the straw during the defibrizing process. In vitro rumen digestibility was significantly higher (P < 0.1) for defibrized than for hammer milled straw. With semisolid culture the level of yeast growth was about three times as high on the defibrized as on hammer milled straw. A scanning electron micrograph revealed that defibrizing removed the waxy surface of the straw as well as separating fiber bundles, so that the surface area of the exposed fiber structure was increased.