Organic Acid Pretreatment Research Articles

Comparative analysis of bioenergy and mycoprotein production from apple pomace: Strategies for enhancement and environmental benefits

Apple pomace constitutes a major waste stream of the food processing industry that is characterized by high concentrations of free sugars and structural carbohydrates. This study comparatively explored alternative apple pomace valorization strategies. To this regard, the integration of hydrothermal and organic acid pretreatment as a strategy to enhance anaerobic digestion biomethane yield and alternative production of mycoprotein as a valuable secondary product via the use of Aspergillus oryzae and Neurospora intermedia edible fungi were investigated. In scenario 1, both pretreatment liquors and solid residues underwent anaerobic digestion to produce biomethane. In scenario 2, pretreatment liquors and solid residues underwent fungal cultivation and anaerobic digestion, respectively. Additionally, to optimize bioenergy yield and minimize wastewater generation in scenario 2, the fungal growth effluent was also subjected to anaerobic digestion. In scenario 1, employing methane for transportation showed the potential to decrease GHG by 314.8 kt CO2 eq, translating to US$72.4 million in social cost savings. Similarly, in scenario 2, replacing edible fungal biomass in the food market could lead to a substantial reduction in emissions by 824.2 kt CO2 eq and a corresponding US$227.0 million in social cost savings.

Effect of hydrothermal-acid pretreatment on methane yield and microbial community in anaerobic digestion of rice straw

Hydrothermal pretreatment has been proposed to enhance straw methane yield during anaerobic digestion recently. However, the combined effect of hydrothermal and organic acid pretreatment (HTOAP) needs further investigation. This study identified optimal pretreatment at 120 °C with 3 % acetic acid for 24 h by orthogonal design method. The HTOAP increased the reducing sugar content by destroying the lignocellulosic structure. A 79 % increment of methane production after HTOAP was observed compared to the untreated group. Microbial analysis showed that HTOAP enriched the relative abundance of lignocellulose-degraders, such as W5053, Thermanaerovibrio, Caldicoprobacter, as well as the syntrophic acetate oxidizing bacteria Syntrophaceticus. Moreover, Methanobacterium conducted hydrogenotrophic methanogenesis dominantly. Furthermore, the potential function analysis showed that HTOAP stimulated the expression of key enzymes in the hydrogenotrophic pathway, including carbon-monoxide dehydrogenase (EC 1.2.7.4) and coenzyme F420 hydrogenase (EC 1.12.98.1). This investigation illustrated the potential of HTOAP of rice straw to facilitate methane production.

Enhanced nutrient recovery from anaerobically digested poultry wastewater through struvite precipitation by organic acid pre-treatment and seeding in a bubble column electrolytic reactor

Limited mineralization of organic phosphorus to phosphate during the anaerobic digestion process poses a significant challenge in the development of cost-effective nutrient recovery strategies from anaerobically digested poultry wastewater (ADPW). This study investigated the influence of organic acids on phosphorus solubilization from ADPW, followed by its recycling in the form of struvite using a bubble column electrolytic reactor (BCER) without adding chemicals. The impact of seeding on the efficiency of PO43− and NH3-N recovery as well as the size distribution of recovered precipitates from the acid pre-treated ADPW was also evaluated. Pre-treatment of the ADPW with oxalic acid achieved complete solubilization of phosphorus, reaching ∼100% extraction efficiency at pH 2.5. The maximum removal efficiency of phosphate and ammonia-nitrogen from the ADPW were 88.9% and 90.1%, respectively, while the addition of 5 and 10 g/L struvite seed to the BCER increased PO43− removal efficiency by 9.6% and 11.5%, respectively. The value of the kinetic rate constant, k, increased from 0.0176 min−1 (unseeded) to 0.0198 min−1, 0.0307 min−1, and 0.0375 min−1 with the seed loading rate of 2, 5, and 10 g/L, respectively. Concurrently, the average particle size rose from 75.3 μm (unseeded) to 82.1 μm, 125.7 μm, and 148.9 μm, respectively. Results from XRD, FTIR, EDS, and dissolved chemical analysis revealed that the solid product obtained from the recovery process was a multi-nutrient fertilizer consisting of 94.7% struvite with negligible levels of heavy metals.

Effect of organic acid-soaking and sonication on the formation of volatile compounds and α-dicarbonyl compounds in Robusta coffee

In this study, the effects of organic acid-soaking (malic, citric, tartaric, and succinic acid) and sonication on the formation of flavor and α-dicarbonyl compounds in Robusta (C. canephora syn. Coffea robusta) green beans were investigated. A total of 20 volatile compounds were identified in Robusta coffee. Furfural and 5-methyl furfural, two dominant volatile compounds in Arabica coffee, increased after organic acid pretreatment. In Robusta coffee processed from 3% malic acid-soaked coffee beans, furfural and 5-methyl furfural increased by 90.99% and 24.92%, respectively, compared to the control. In Robusta coffee processed from 3% malic acid-sonicated (280 W, 1 h) coffee beans, furfural and 5-methyl furfural increased by 236.03% and 114.77%, respectively. α-Dicarbonyls (glyoxal, methylglyoxal, and diacetyl) were significantly (p < 0.05) decreased in all Robusta coffees after organic acid pretreatment. In Robusta coffee processed from coffee beans soaked and sonicated in tartaric acid solution, the α-dicarbonyls decreased by up to 44% and 58%, respectively, compared to the control. This study suggested the pretreatment methods to enhance the flavor substances and reduce the α-DCs in Robusta coffee.

Efficient co-production of xylo-oligosaccharides and fermentable sugars from sugarcane bagasse by glutamic acid pretreatment

In the production of xylo-oligosaccharides (XOS) by organic acid pretreatment, it is often difficult to isolate organic acids from XOS. Here, an acidic amino acid, glutamic acid (GA), was used to pretreat sugarcane bagasse (SCB) to prepare XOS and fermentable sugars. The effects of GA concentration, hydrolysis temperature, and pretreatment time on the yield and polymerization distribution of XOS were investigated. After hydrolysis by 0.2 M GA at 140 °C for 30 min, the maximum yield of X2-5 was 53.3%, and the concentrations of xylose and furfural were 1.8 g/L and 0.1 g/L, respectively. Meanwhile, GA increased the pore size and porosity of SCB as well as the number of functional groups of amino acid residues, which improved the enzymatic efficiency and the maximum yield of glucose was 95.3%. Thus, GA pretreatment provides a more economical, environmentally friendly and sustainable method for the co-production of XOS and glucose from SCB.

Novel dual-action vanillic acid pretreatment for efficient hemicellulose separation with simultaneous inhibition of lignin condensation

Aromatic acids play a selective role in the separation of hemicellulose. Phenolic acids have demonstrated an inhibitory effect on lignin condensation. In the current study, vanillic acid (VA), which combines the characteristics of aromatic and phenolic acids, is used to separate eucalyptus. The efficient and selective separation of hemicellulose is achieved simultaneously at 170 °C, 8.0% VA concentration, and 80 min. The separation yield of xylose increased from 78.80% to 88.59% compared to acetic acid (AA) pretreatment. The separation yield of lignin decreased from 19.32% to 11.19%. In particular, the β-O-4 content of lignin increased by 5.78% after pretreatment. The results indicate that VA, as a “carbon positive ion scavenger”, it preferentially reacts with the carbon-positive ion intermediate of lignin. Surprisingly, the inhibition of lignin condensation is achieved. This study provides a new starting point for the development of an efficient and sustainable commercial technology by organic acid pretreatment.

Enhancing enzymatic saccharification of sunflower straw through optimal tartaric acid hydrothermal pretreatment

Sunflower straw, a usually neglected and abundant agricultural waste, has great potential for contributing to environmental protection realizing its high-value of valorization if utilizing properly. Because hemicellulose contains amorphous polysaccharide chains, relatively mild organic acid pretreatment can effectively reduce its resistance. Through hydrothermal pretreatment, sunflower straw was pretreated in tartaric acid (1 wt%) at 180 °C for 60 min to enhance its reducing sugar recovery. After tartaric acid-assisted hydrothermal pretreatment, 39.9% of lignin and 90.2% of xylan were eliminated. The reducing sugar recovery increased threefold, while the solution could be effectively reused for four cycles. The properties of more porous surface, improved accessibility, and decreased surface lignin area of sunflower straw were observed through various characterizations, which explained the improved saccharide recovery and provided a basis for the mechanism of tartaric acid-assisted hydrothermal pretreatment. Overall, this tartaric acid hydrothermal pretreatment strategy greatly provided new impetus for the biomass refinery.

Rapid and mild fractionation of hemicellulose through recyclable mandelic acid pretreatment

The development of organic acid pretreatments from biological sources is essential to facilitate the progress of green and sustainable chemistry. In this study, the effectiveness of mandelic acid pretreatment (MAP) was analyzed for eucalyptus hemicellulose separation. 83.66% of xylose was separated under optimal conditions (temperature: 150 °C; concentration: 6.0 wt%; time: 80 min). The hemicellulose separation selectivity is higher than acetic acid pretreatment (AAP). The stable and effective separation efficiency (56.55%) is observed even after six reuses of the hydrolysate. Higher thermal stability, larger crystallinity index and optimized surface element distribution in the samples were demonstrated by MAP. Lignin condensation is effectively inhibited through MAP, as determined from the structural of different lignin. In particular, the demethoxylation of lignin by MA was found. These results open up a new way to construct a novel organic acid pretreatment for separating hemicellulose with high efficiency.

Mannitol assisted oxalic acid pretreatment of poplar for the deconstruction and separation of hemicellulose

The effect of mannitol (MA) on the poplar separation using mannitol-assisted oxalic acid (M/OA) pretreatment was revealed. The effects of reaction parameters on the separation efficiency were studied. The optimized conditions were OA 7.0%, MA 7.0%, temperature 150 °C, and time 60 min. The hemicellulose separation was 79.08%. The separation of cellulose and lignin decreased from 12.43% and 21.82–8.58% and 16.11%, respectively, under hemicellulose separation similar to those of conventional OA pretreatment. Smooth fiber surfaces with less lignin deposition were observed. There were more β-O-4 and fewer β-β in lignin. Additionally, larger amounts of aliphatic hydroxyl groups and smaller amounts of phenolic hydroxyl groups were observed, which implies that MA addition prevented lignin from condensing. An effective and environmentally friendly separation of hemicellulose was achieved by M/OA pretreatment. This provides a practical approach for resolving the stubborn problems of lignin cleavage and condensation during organic acid pretreatment.

Pretreatment of poplar with eco-friendly levulinic acid to achieve efficient utilization of biomass

Organic acid pretreatment is an effective method for green separation of lignocellulosic biomass. However, repolymerization of lignin seriously affects the dissolution of hemicellulose and the conversion of cellulose during organic acid pretreatment. Therefore, a new organic acid pretreatment, levulinic acid (Lev) pretreatment, was studied for the deconstruction of lignocellulosic biomass without adding additional additives. The preferred separation of hemicellulose was realized at Lev concentration 7.0%, temperature 170 °C, and time 100 min. The separation of hemicellulose increased from 58.38% to 82.05% compared with acetic acid pretreatment. It was found that the repolymerization of lignin was effectively inhibited in the efficient separation of hemicellulose. This was attributed to the fact that γ-valerolactone (GVL) is a good green scavenger of lignin fragments. The lignin fragments in the hydrolysate were effectively dissolved. The results provided theoretical support for creating green and efficient organic acid pretreatment and effectively inhibiting lignin repolymerization.

Pretreatment with dilute maleic acid enhances the enzymatic digestibility of sugarcane bagasse and oil palm empty fruit bunch fiber

Lignocellulose is resistant to degradation and requires pretreatment before hydrolytic enzymes can release fermentable sugars. Sulfuric acid has been widely used for biomass pretreatment, but high amount of degradation products usually occurred when using this method. To enhance accessibility to cellulose, we studied the performances of several dilute organic acid pretreatments of sugarcane bagasse and oil palm empty fruit bunch fiber. The results revealed that pretreatment with maleic acid yields the highest xylose and glucose release among other organic acids. The effects of concentration, duration of heating and heating temperature were further studied. Dilute maleic acid 1 % (w/w) pretreatment at 180 °C was the key to its viability as a substitute for sulfuric acid. Moreover, maleic acid did not seem to highly promote the formation of either furfural or 5-HMF in the liquid hydrolysate after pretreatment.

Efficient separation of eucalyptus hemicellulose and improvement of the stability of the remaining components by 1-amino-2-naphthol-4-sulfonic acid pretreatment

High selectivity of hemicellulose separation is difficult to achieve using organic acid pretreatment. This is attributed to the depolymerization and polycondensation of lignin, which is accompanied by the separation of hemicellulose. In this study, the separation of eucalyptus components was studied by 1-amino-2-naphthol-4-sulfonic acid (ns-A) pretreatment. An organic acid concentration of 9% at a pretreatment temperature of 170 °C performed for 80 min was determined as the optimum condition for ns-A pretreatment. The separation yield of hemicellulose increased to 82.76% compared with that of p-toluenesulfonic acid pretreatment. The separation yield of lignin decreased from 30.20% to 8.43%. The surface coverage of lignin increased from 0.70% to 0.83%. Furthermore, the recovery yield of the organic acids in the ns-A pretreatment process was 91%. The ns-A-pretreated acid solution provided stable, efficient separation within six reuse cycles. Lignin in eucalyptus was found to be rich in aliphatic hydroxyl groups and guaiacyl-syringyl units. Therefore, the depolymerization and polycondensation of lignin was inhibited while efficiently separating hemicellulose during ns-A pretreatment. This study provides a new method for the efficient separation of lignocellulosic biomass.

Improvement of Water Hyacinth Bioconversion by Different Organic and Mineral Acid Pretreatment and the Effect of Post-pretreatment Washing

Improvement of Water Hyacinth Bioconversion by Different Organic and Mineral Acid Pretreatment and the Effect of Post-pretreatment Washing

Superior separation of hemicellulose-derived sugars from eucalyptus with tropic acid pretreatment

Organic acid pretreatments can efficiently separate biomass-based hemicellulose and selectively produce hemicellulose-derived sugars. In this study, hemicellulose is separation as xylose, oligosaccharides in the tropic acid-catalyzed hydrothermal pretreatment of eucalyptus. The maximum yield of hemicellulose-derived sugars (85.78 %) with 71.25 % xylose selectivity (based on the total xylose in raw material) was achieved in the hydrolysate under optimal conditions (5 % TA, 160 ℃, 80 min). The yield of hemicellulose-derived sugar and the separation yield of hemicellulose increased by 11.06 % and 11.45 % compared with glycolic acid pretreatment in the similar severity factor. The separation yield of cellulose and lignin was decreased by 4.23 % and 0.98 %, respectively. This resulted in residual solids with higher biological stability (higher fiber crystallinity index, higher thermal stability, and higher lignin content). Therefore, higher hemicellulose separation selectivity and rich hemicellulose-derived sugars were obtained using TA pretreatment. The work would bring up a new method for biomass refining.

In-depth investigation of the bioethanol and biogas production from organic and mineral acid pretreated sugarcane bagasse: Comparative and optimization studies

Organic acid pretreatment has generated much interest as one of the high potential methods for promoting enzymatic saccharification of lignocellulosic materials. Organic acids are preferred during pretreatment because they are less hazardous than conventional ones and produce less inhibitory fermentation by-products. In the present study, three organic acids (oxalic acid, citric acid, and acetic acid) and inorganic acid (hydrochloric acid) were studied to produce bioethanol and biogas from sugarcane bagasse. An optimization design (Box–Behnken Design (BBD)) among different optimization designs of response surface methodology (RSM) was considered to determine the pretreatment optimum conditions. On this basis, citric acid (CA)pretreatment resulted in maximum glucose yield (7.93 mg/mL) during saccharification. FTIR analysis of the pretreated samples showed that the structure of lignocellulose was changed in higher proportions for the sample pretreated with an organic acid. An increase in cellulose portion and maximum removal of hemicellulose with lower furan generations was observed in organic acid samples. In this study, the maximum solubilization of hemicellulose in hydrochloric acid was also observed due to the abundance of free H+ ions to catalyze the reaction. The ethanol and biogas yield increased by 1.96 and 1.85-fold for citric acid and oxalic acid pretreated sugarcane bagasse, respectively than untreated samples. The present study concluded that oxalic acid and citric acid pretreatment showed the potential to enhance the yield of bioethanol and biogas, respectively. An organic acid in the pretreatment of lignocellulosic biomass can replace traditional methods of using inorganic acids in biorefineries.

Organic Acid Pretreatments and Optimization Techniques for Mixed Vegetable Waste Biomass Conversion into Biofuel Production

Organic Acid Pretreatments and Optimization Techniques for Mixed Vegetable Waste Biomass Conversion into Biofuel Production

Kinetics of Lignin Separation during the Atmospheric Fractionation of Bagasse with p-Toluenesulfonic Acid.

As a green and efficient component separation technology, organic acid pretreatment has been widely studied in biomass refining. In particular, the efficient separation of lignin by p-toluenesulfonic acid (p-TsOH) pretreatment has been achieved. In this study, the mechanism of the atmospheric separation of bagasse lignin with p-TsOH was investigated. The separation kinetics of lignin was analyzed. A non-simple linear relationship was found between the separation yield of lignin and the concentration of p-TsOH, the temperature and the stirring speed. The shrinking nucleus model for the separation of lignin was established based on the introduction of mass transfer and diffusion factors. A general model of the total delignification rate was obtained. The results showed that the process of lignin separation occurred into two phases, i.e., a fast stage and a slow stage. The results provide a theoretical basis for the efficient separation of lignin by p-TsOH pretreatment.

Effect of organic acid pre-treatment on polyphenol oxidase induced browning and sensory quality of frozen yam chips

Yam Dioscorea spp suffers about 30% postharvest losses annually. Processing into convenience products such as yam chips prolong shelf life although the action of enzymes including polyphenol oxidase (PPO) and peroxidase (POD) may affect the quality if not precluded. Pre-treatment of cut yam with pH modifiers and antioxidants before storage could reduce enzymatic browning. In this study we investigated the effectiveness of ascorbic acid, citric acid and lime juice treatment and 5 weeks (w) of frozen storage in reducing browning in yam chips without affecting sensory quality. PPO and POD activity of freshly prepared yam chips pre-treated with citric acid, ascorbic acid or lime juice and stored frozen at -18 °C for 5 weeks was determined. The yam chips were fried and the moisture, oil content and colour determined. Consumer acceptability sensory evaluation was conducted for the week 0 and 5 of stored samples. POD activity was significantly reduced (50%) by treatment with citric acid after five-weeks of frozen storage while treatment with ascorbic acid and lime juice had no effect on the enzyme activity. There was no significant difference in lightness between the different treatments although treated samples differed significantly from the untreated. Moisture content of all samples were lower after storage while oil content of the various treatments was significantly different. Notwithstanding these differences, consumer acceptability was not different between the various treatment and storage periods. Pre-treated frozen yam chips have a good consumer acceptance and potential for commercial application. Developing this product will add value to yams and reduce huge postharvest losses.

Optimization of Different Acid-Catalyzed Pretreatments on Co-Production of Xylooligosaccharides and Glucose from Sorghum Stalk.

There is an increasing emphasis on the transformation of lignocellulosic biomass into versatile products. The feasibility of preparing xylooligosaccharides (XOS) by hydrolysis of sorghum stalk (SS) using organic and inorganic acids was studied. The influences of different acids (gluconic acid, acetic acid, sulfuric acid, and oxalic acid), process time and temperature on the hydrolysis of SS were explored. The findings indicated XOS yield can be maintained at a high level under different conditions with organic acid pretreatments. Optimum yield of XOS (39.4%) was obtained using sulfuric acid (pH 2.2) at 170 °C and 75 min of process time. It is suggested when reaction temperature and time were increased, both X5 and X6 are cracked into XOS with lower molecular mass such as X2, X3, and X4. Moreover, the results based on mass balance showed that up to 110 g (XOS) plus 117 g (glucose) can be recovered from 1000 g of SS. Results will give insights into establishing an efficient acid pretreatment of sorghum stalk to coproduction of XOS and glucose.

Flotation enhancement of low-grade bauxite using oxalic acid as surface pretreatment agent

Surface pretreatment on minerals prior to flotation was proved to increase the selectivity of separation process. Organic acid pretreatment of low-grade diasporic-bauxite was conducted, and the effects of oxalic acid on bauxite flotation were investigated in this work. The oxalic acid pretreatment mechanisms were studied by adsorption measurements, zeta potential testing, XPS analysis, and ICP analysis. The flotation results showed that the oxalic acid treatment could significantly improve Al2O3 recovery from 75.39% to 81.88% and decrease SiO2 recovery from 53.26% to 47.30%. The adsorption capacity of diaspore for sodium oleate (NaOL) increased by 8.50%, while that of kaolinite decreased by 11.72%. XPS analysis revealed that oxalic acid treatment improved the relative contents of unsaturated Al at diaspore surface beneficial to the adsorption of NaOL. While the relative content of Al at kaolinite surface was decreased due to the Al dissolution revealed by ICP results. Zeta potential analysis indicated that oxalic acid changed the surface property of minerals favorable for the selective adsorption of NaOL on diaspore surface rather than kaolinite surface. These findings provided a promising direction for surface pretreatment of low-grade bauxite using oxalic acid for the improvement of the flotation desilication.