Liquid Hydrolysate Research Articles

Optimized Furfural Production Using the Acid Catalytic Conversion of Xylan Liquor from Organosolv-Fractionated Rice Husk

This study determined the optimal production of furfural (FuR) from liquid hydrolysate xylan liquor obtained through a two-stage pretreatment process using NaOH for de-ashing and EtOH for the delignification of raw rice husk (RH). The de-ashing pretreatment was conducted at 150 °C, with 6.0% (w/v) NaOH and a reaction time of 40 min. The optimal conditions for delignification pretreatment, performed using an organosolv fractionation method with EtOH, were a reaction temperature of 150 °C, 60% (v/v) EtOH, 0.25% (w/v) H2SO4, and a reaction time of 90 min. Through a two-stage pretreatment process, a liquid hydrolysate in the form of xylan liquor was obtained, which was subjected to an acid catalytic conversion process to produce FuR. The process conditions were varied, with reaction temperatures of 130–170 °C, H2SO4 catalyst concentrations of 1.0–3.0 wt.%, and reaction times of 0–90 min. The Response Surface Methodology tool was used to identify the optimal FuR yield from xylan liquor. Ultimately, the optimal process conditions for the acid catalytic conversion were found to be a substrate-to-catalyst ratio of 2:8, a reaction temperature of 168.9 °C, a catalyst concentration of 1.9 wt.%, and a reaction time of 41.24 min, achieving an FuR yield of 67.31%.

Investigating the Potential of Grass Biomass (Thysanolaena latifolia) as an Alternative Feedstock for Sugar Platforms and Bioethanol Production

Bioethanol, a lignocellulosic biofuel, has increased energy sustainability and lessened the environmental effects associated with energy production. Thysanolaena latifolia is a common weed found in the northern part of Thailand that is considered non-food biomass, with a high biomass productivity of approximately 10.2 kg/year. Here, we evaluated the potential of T. latifolia biomass as an environmentally friendly material source for producing alternative bioethanol. To this end, we treated the feedstock under mild conditions using various concentrations of phosphoric acid to create ideal conditions for enzymatic hydrolysis. Pretreatment with 75% phosphoric acid yielded the highest solid recovery (55.8 ± 0.6%) and glucans (93.0 ± 0.3%). Additionally, the hydrolysis efficiency and glucose yield of treated biomass were significantly improved. As a result, the liquid hydrolysate from T. latifolia used for ethanol fermentation by Saccharomyces cerevisiae TISTR 5339 generated 8.9 ± 0.0 g/L ethanol. These findings demonstrate that glucose derived from liquid hydrolysate is a promising sustainable carbon source for producing ethanol from T. latifolia feedstock. Thus, using T. latifolia as a feedstock for generating ethanol can improve the efficiency of bioenergy production.

Bioactive, textural and sensory attributes of soft confections enriched with plant protein hydrolysates

AbstractSoft confections can serve as a reservoir for bioactive peptide delivery in both functional food and food supplement applications. In this study, pectin-based soft confections were fortified with proteolytic plant protein hydrolysates and the residual bioactivity of hydrolysates was studied after processing or simulated digestion. Cold press sunflower or hazelnut cakes were used in the manufacture of protein isolates based on an alkali extraction-isoelectric precipitation (AE-IP) method. Trypsin or bromelain were utilized in the proteolysis of the isolates and thus prepared liquid hydrolysates were used in confectionery manufacture. DPP-IV (dipeptidyl peptidase-IV) inhibitory activity (i.e., in vitro antidiabetic activity) and antioxidative activities were measured. In addition, sensory and textural attributes were investigated. In all cases, a significant concentration of hydrolysates were added to the confections (27%), which lead to significant changes in color, texture and sensory acceptance. The peptide profile and size distribution mostly altered such characteristics, while observed bioactivity was significant after processing. Simulated digestion enhanced DPP-IV inhibitory activity up to approx. 40%, whereas antioxidative performance decreased. While the applicability of the current findings is limited by hydrolysate solubility, ingredient interactions, and processing costs, the relevance of degree of hydrolysis (DH%), peptide characteristics and phenolic-peptide interactions on product quality and eventual bioactivity are being discussed.

Development of an Integrated Bioprocess System for Bioethanol and Arabitol Production from Sugar Beet Cossettes.

An innovative integrated bioprocess system for bioethanol production from raw sugar beet cossettes (SBC) and arabitol from remaining exhausted sugar beet cossettes (ESBC) was studied. This integrated three-stage bioprocess system is an example of the biorefinery concept to maximise the use of raw SBC for the production of high value-added products such as sugar alcohols and bioethanol. The first stage of the integrated bioprocess system was simultaneous sugar extraction from SBC and its alcoholic fermentation to produce bioethanol in an integrated bioreactor system (vertical column bioreactor and stirred tank bioreactor) containing a high-density suspension of yeast Saccharomyces cerevisiae (30 g/L). The second stage was the pretreatment of ESBC with dilute sulfuric acid to release fermentable sugars. The resulting liquid hydrolysate of ESBC was used in the third stage as a nutrient medium for arabitol production by non-Saccharomyces yeasts (Spathaspora passalidarum CBS 10155 and Spathaspora arborariae CBS 11463). The obtained results show that the efficiency of bioethanol production increased with increasing temperature and prolonged residence time in the integrated bioreactor system. The maximum bioethanol production efficiency (87.22 %) was observed at a time of 60 min and a temperature of 36 °C. Further increase in residence time (above 60 min) did not result in the significant increase of bioethanol production efficiency. Weak acid hydrolysis was used for ESBC pretreatment and the highest sugar yield was reached at 200 °C and residence time of 1 min. The inhibitors of the weak acid pretreatment were produced below bioprocess inhibition threshold. The use of the obtained liqiud phase of ESBC hydrolysate for the production of arabitol in the stirred tank bioreactor under constant aeration clearly showed that S. passalidarum CBS 10155 with 8.48 g/L of arabitol (YP/S=0.603 g/g and bioprocess productivity of 0.176 g/(L.h)) is a better arabitol producer than Spathaspora arborariae CBS 10155. An innovative integrated bioprocess system for the production of bioethanol and arabitol was developed based on the biorefinery concept. This three-stage bioprocess system shows great potential for maximum use of SBC as a feedstock for bioethanol and arabitol production and it could be an example of a sustainable 'zero waste' production system.

Isolation of xylose-utilizing yeasts from oil palm waste for xylitol and ethanol production

The energy crisis triggers the use of energy sources that are renewable, such as biomass made from lignocellulosic materials, to produce various chemical compounds for food ingredients and biofuel. The efficient conversion of lignocellulosic biomass into products with added value involves the activity of microorganisms, such as yeasts. For the conversion, microorganisms must be able to use various sugars in lignocellulosic biomass, including pentose sugars, especially xylose. This study aims to isolate xylose-utilizing yeasts and analyze their fermentation activity to produce xylitol and ethanol, as well as their ability to grow in liquid hydrolysate produced from pretreated lignocellulosic biomass. Nineteen yeast isolates could grow on solid and liquid media using solely xylose as a carbon source. All isolates can grow in a xylose medium with incubation at 30 °C, 37 °C, 42 °C, and 45 °C. Six isolates, namely SLI (1), SL3, SL6, SL7, R5, and OPT4B, were chosen based on their considerable growth and high xylose consumption rate in a medium with 50 g/L xylose with incubation at 30 °C for 48 h. Four isolates tested, namely SLI (1), SL6, SL7, and R5, can produce xylitol in media containing xylose carbon sources. The concentration of xylitol produced was determined using high-pressure liquid chromatography (HPLC), and the results ranged from 5.0 to 6.0 g/L. Five isolates tested, namely SLI (1), SL6, SL3, R5, and OPT4B, can produce ethanol. The ethanol content produced was determined using gas chromatography (GC), with concentrations ranging from 0.85 to 1.34 g/L. Three isolates, namely SL1(1), R5, and SL6, were able to produce xylitol and ethanol from xylose as carbon sources and were also able to grow on liquid hydrolyzate from pretreated oil palm trunk waste with the subcritical water method. The three isolates were further analyzed using the 18S rDNA sequence to identify the species and confirm their phylogenetic position. Identification based on DNA sequence analysis revealed that isolates SL1(1) and R5 were Pichia kudriavzevii, while isolate SL6 was Candida xylopsoci. The yeast strains isolated from this study could potentially be used for the bioconversion process of lignocellulosic biomass waste to produce value-added derivative products.Graphical

Application of an Integrated Granular and Suspended Sludge Methane Reactor for a Two-Stage Anaerobic Digestion System to Deal with Biodegradable Municipal Solid Waste

This study aims to investigate the performance of a two-stage anaerobic digestion system using a hybrid methane reactor to deal with biodegradable municipal solid waste. The reactor allowed both suspended sludge and granular sludge to work together. The feedstock was fermented in one continuous stirred tank at different pH conditions for 5 d. Furthermore, the liquid hydrolysate was diluted and pumped into a methane reactor with different organic loading rates. In the fermentative reactor, raising the pH condition from 4.5 to 6.5 caused a sharp increase in volatile fatty acids concentration, mainly due to the increase in acetate and propionate. The efficiency of the methane reactor was proven by the results of hydrodynamic analysis and biogas production. The relationship between biogas production and operating parameters in this reactor was modeled using a quadratic multivariate regression model. Overall, by maintaining the fermentative reactor at a pH of 6.0–6.5, the methane reactor was able to achieve an organic loading rate of 7.6 g-TS.L−1·d−1 with outstanding biogas quality and yield. In terms of microbiology, the most dominant phyla in the reactor included Firmicutes, Bacteroidetes, Proteobacteria, Euryarchaeota, Synergistetes, and Chloroflexi. Among them, the species with the highest relative abundance in granular sludge was Firmicutes, while that in suspended sludge was Bacteroidetes.

Biogas Production and Energy Balance in a Two-Stage Anaerobic Digestion of Fruit and Vegetable Waste: Thermophilic versus Mesophilic

This study aimed to investigate biogas production and energy balance in a two-stage anaerobic digestion system of fruit/vegetable waste under thermophilic and mesophilic conditions. Firstly, the feedstock was hydrolyzed and acidified in an acidic reactor at 37 °C with a retention time of 5 d. Then, the liquid hydrolysate was collected and pumped into an up-flow methane reactor under a mesophilic temperature with a retention time of 5 d and a thermophilic condition with a retention time of 3 d. The experimental results showed that in the thermophilic methane reactor, the COD removal, biogas yield, and methane concentration were 96.3%, 492 mL/g-VS, and 70.4%, respectively. These values were 3%, 10%, and 3% higher, respectively, than those obtained in the mesophilic methane reactor. In terms of energy, the mesophilic and thermophilic methane reactors consumed the same thermal energy demand for temperature control. They were much lower than the heat values produced by the power engine. The two-stage anaerobic digestion system using a thermophilic methane reactor obtained a gross energy of 11.20 kJ/g-VS and a net energy of 9.83 kJ/g-VS. These values were 13.2% and 14.8% higher, respectively, than those obtained by the system with a mesophilic condition. Moreover, the use of a thermophilic reactor helped reduce the reactor volume by 40%, leading to significant investment cost savings.

Comprehensive Treatment Strategy for Banana Inflorescence Bract to Synthesize Biodiesel and Bioethanol Through Fungal Biorefinery

Banana inflorescence bract (BIB), an agro-waste is sporadically explored for second-generation biofuel production in spite of having considerable holocellulosic composition (cellulose-35.56%, w/w; hemicellulose-22.41%, w/w). In this study, an attempt has been made to utilize this substrate for fermentable sugars (pentose-C5 and hexose-C6) extraction which were employed for the co-production of microbial lipids and ethanol using Rhodosporidium toruloides NCIM 3547 and Saccharomyces cerevisiae respectively. Since, a considerable amount of lignin (8.78%, w/w) is present in BIB, a hybrid pretreatment and carbohydrate hydrolysis through microwave (160 W) assisted mild H2SO4 acid 2.5% (v/v) was adopted. The resultant liquor contains holocellulosic sugars (C5 and C6 sugars), out of which xylose (10.40 ± 0.49 g/L) and glucose (51.48 ± 1.14 g/L). Hence, it was used as the growth medium for R. toruloides to produce lipids i.e., single cell oil (SCO). The maximum lipid content was found to be 44.89 ± 1.25 (%, w/w) containing total saturated fatty acids of 89.07% which justifies its potential application in biodiesel production. On the other hand, the pretreated solid fraction containing cellulose was saccharified using cellulolytic enzyme produced by Aspergillus sp. with saccharification (%) of 69.99 ± 0.30 (%, v/w) and yield of 27.22 ± 0.33 g/L of reducing sugar. This enzymatic hydrolysate was used for ethanol production by Saccharomyces cerevisiae resulting in an ethanol yield of 12.70 ± 0.09 g/L and productivity of 0.132 g/L/h. Based on this outcome, a sustainable route for agro-waste management of BIB was laid by favouring the integrated production of biodiesel and bioethanol towards a biorefinery approach. Exploration and utilization of an agro-waste, banana inflorescence bract is established as a potent feedstock for the co-production of single cell oil and bioethanol is reported for the first time. Microwave-assisted mild acid pretreatment was performed for effective delignification and hydrolysis of holocellulosic components. The resultant liquid hydrolysate consisting of lignin degradatory compounds, pentose (xylose) and hexose (glucose) sugars was used as a growth medium for producing single cell oil, proving its potential application in biodiesel production. Further, the pretreated solid cellulosic fraction was saccharified using crude cellulolytic enzymes and an enzymatic hydrolysate was used for the production of bioethanol through two different fermentative strategies. This study reveals that banana inflorescence bract could act as suitable biomass towards the biorefinery approach. Its complete utilization paved the way for agro-waste management that is not in existence so far according to the authors’ knowledge

Inhibition of cellulase activity by liquid hydrolysates from hydrothermally pretreated soybean straw

The one-pot biomass conversion process is a promising strategy to minimize potential product loss and reduce processing costs. However, this strategy has technical limitations due to the inhibitory effects of biomass components like lignin as well as the generated inhibitors (e.g., furans, phenols) during biomass processing. In this study, the inhibitory effects of liquid hydrolysates formed by hydrothermal pretreatment of soybean straw with either sodium hydroxide (NaOH) or hydrogen peroxide (H2O2) on cellulolytic enzyme activity were investigated. Hydrothermal pretreatment of soybean straw (10% w/v) was carried out with either sodium hydroxide (1% v/v) or hydrogen peroxide (1% v/v) at 121°C for 60 min to evaluate the effect of water-soluble inhibitors released from soybean pretreatment on cellulolytic enzyme activity. The fraction of cellulose in pretreated solids (1% w/v glucan) was enzymatically hydrolyzed for 72 h with 45 IU/g glucan (corresponding to 25 mg enzyme protein/g glucan) in the presence of either buffer or liquid hydrolysate generated from the pretreatments. Hydrolysis of NaOH and H2O2 pretreated solids resulted in 57% and 39% of glucose yields in buffer, respectively. In the presence of the liquid hydrolysates, NaOH and H2O2 pretreated biomass showed 20% and 30% glucose yield, respectively, indicating the enzyme suppression by inhibitors in the liquid hydrolysates. Of the enzyme activities in hydrolysates tested, NaOH hydrolysate showed a higher inhibitory effect on enzyme activities (mainly β-glucosidase) compared to H2O2 liquid, where enzyme deactivation has a first-order correlation and the manner in which the vacuum-filtered inhibitors were generated from pretreated soybean straw.

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.

Physicochemical Properties of Single Cell Oil Extracted from Oleaginous Yeasts

The study aimed at extracting single cell oil (SCO) from some oleaginous yeasts living on wheat straw and sugarcane molasses media and to determine physicochemical properties of the produced oil for further assessment as edible oil. Thirty samples of yeasts were isolated according to the different methods based on the source of isolates. The effectiveness of oleaginous yeast to produce the single cell oil was studied, when the yeast was grown on two types of wheat straw media (detoxified liquid hydrolysate (DLH) and non-detoxified liquid hydrolysate (NDLH)), and molasse media. Single cell oil was extracted by hexane. Saccharomyces cerevisiae and Pichia guilliermondii were used to produce SCO. SCO produced from oleaginous yeasts in sugarcane molasses media was significantly (P≤0.05) higher than that produced in wheat straw media. DLH of wheat straw gave higher productivity of oil than NDLH wheat straw. Generally, S. cerevisiae gave higher oil productivity (84 %), compared to P. guilliermondii (52 %).The results indicated that most of the physicochemical properties of extracted oil were found to be within the recommended limit of the common edible oil reported, except for the iron content; it ranged from 21 to 24 mg/kg, which was 4-5 times more than the permissible level of that of the Codex Alimentarius Commission. In addition, single cell oil produced by molasses contained omega-3 fatty acids such as eicosapentaenoic and docosahexaenoic which are not found in vegetable oil. Also the unsaturated fatty acids of SCO produced in wheat straw media were higher than that produced in molasses media. The fatty acid profile of SCO produced in molasses media was different from that of vegetable oils. The good physicochemical characteristics and fatty acids profile of SCO from wheat straw make it safe and a promising potential raw material for production of edible oil. The result of this study suggests the isolation of oleaginous yeast in order to be used in the edible oil production

Screening and Molecular Characterization of Oleaginous Yeasts and Their Potentiality for Single Cell Oil Production

The study aimed to isolate oleaginous yeasts from different sources (rotten fruits, fruit juices, milk, fish and air) and to identify and to study the possibility of production of single cell oil (SCO) from wheat straw and sugarcane molasses media. Thirty samples of yeasts were isolated using different methods according to the source of isolates. The isolated yeasts were characterized using microscopic appearance, colony morphology, physiological tests, assimilation tests and molecular identification. The effectiveness of oleaginous yeast to produce the single cell oil was studied, by growing the yeast on two types of wheat straw media (detoxified liquid hydrolysate (DLH) and non-detoxified liquid hydrolysate (NDLH)), and molasse media. Single cell oil was extracted by hexane. Eighteen isolates were found to be yeast, and the profile of ten yeast samples was identified as Saccharomyces cerevisiae, while, one sample was identified as Pichia guilliermondii. DLH wheat straw gave higher productivity of oil than NDLH wheat straw. Generally, S. cerevisiae gave higher oil productivity (84 %), compared to P. guilliermondii (52 %).

Promoting the overall energy profit through using the liquid hydrolysate during microwave hydrothermal pretreatment of wheat straw as co-substrate for anaerobic digestion

Liquid hydrolysate (LH) derived from the microwave hydrothermal pretreatment (MHP) of wheat straw (WS) was anaerobically digested together with the solid residual to promote the overall energy profit. Different MHP temperatures (90, 120, 150, 180 °C) and retention times (10, 20, 40 min) were investigated. Increased MHP intensity generated plenty of VFAs (mainly acetate) and phenols in the LH, implying the double-side effect of LH on AD. The highest methane production of 227.92 mL CH4·gVS-1 Raw was obtained with MHP at 120 °C for 10 min, 21.53 % higher than the control. While, MHP at 180 °C for 40 min exhibited 29.02 % lower methane production (113.13 mL CH4·gVS-1 Raw) and 115.86 % longer lag phase (3.13 days) than the control. Butyrate fermentation endowed the treatment groups of 180 °C with resilience from the overload and inhibition. Methanosarcina was largely enriched by the abundant acetate in LH on the early stage of anaerobic digestion (AD), especially when with high MHP intensity. Increased abundance of Methanosaeta and Methanobacterium played a crucial role in maintaining methane production at the middle and later stage. The high number of species and evenness in methanogens community were beneficial for the startup of batch AD. Although negative net energy was obtained, the lower ratio of energy input and output compared with the most researches using the solid residual after MHP as the sole substrate for AD demonstrated the contribution of LH to the overall energy profit.

Green and sustainable 'Al-Zr-oligosaccharides' tanning agents from the simultaneous depolymerization and oxidation of waste paper.

Developing chrome-free and sustainable tanning agents is extremely important to the sustainability of the leather industry. Herein, we have synthesized an Al-Zr-oligosaccharides tanning agent via a simultaneous degradation and oxidation of cellulose in waste paper. The influence of the temperature and the concentrations of AlCl3 and H2O2 during the synthesis were thoroughly investigated on the properties of the tanning agent and the leather produced. The synthesis temperature and the concentration of AlCl3 were the factors primarily affecting the effective depolymerization of cellulose. They controlled the conversion of waste paper into oligosaccharides with an appropriate molecular weight to efficiently penetrate the leather matrix. In parallel, the H2O2 concentration substantially influenced the tanning performance of the Al-Zr-oligosaccharides, diminishing the chromaticity of the tanning liquid via oxidation and promoting the conversion of C2/C3/C6-OH moieties into -CHO/-COOH. These functional groups increased the surface charge of the oligosaccharides allowing more effective coordination with Al/Zr, which facilitated the penetration of Al/Zr species into the leather matrix. Once inside the leather matrix, Al and Zr were released and reacted with the collagen fibers in leather, which resulted in effective leather tanning. The process optimization revealed that up to 57% of waste paper could be converted into a low-chromaticity (4350 AU) liquid hydrolysate with the synthesis conducted at 177 °C in a system comprising 47 mM AlCl3 and 5 vol% H2O2. The application of this liquid for tanning provided leather with a shrinkage temperature (86.5 °C) sufficiently high for commercial applications. These excellent results, combined with the intrinsic green nature of our approach, exemplify a step forward to simultaneously reduce pollution and hazards in leather industries giving a second life to waste paper.

Highly efficient fed-batch modes for enzymatic hydrolysis and microbial lipogenesis from alkaline organosolv pretreated corn stover for biodiesel production

High-density culture for microbial lipid preparation from low-cost lignocellulosic feedstocks is crucial for commercial-scale biodiesel production. Herein, fed-batch saccharification of alkaline organosolv pretreatment (AOP) of corn stover at an extremely high solids content of 47% (w/v) released 299.5 g/L of lignocellulosic sugars including 18.3% of soluble oligosaccharides. Three types of liquid hydrolysates for seed culture, fermentation, and feeding during fed-batch culture were obtained from the hydrolysate slurry using a two-step washing strategy with 99.3% of sugars recovery. Cutaneotrichosporon oleaginosum showed excellent capacity for assimilating both monosaccharides and oligosaccharides for lipid production using the fed-batch culture mode. Lipid concentration, content, and yield gained 42.3 g/L, 64.6%, and 20.4 g/100 g, respectively. Turbid hydrolysate collected with high recovery of high-concentration sugars and simplified process could be directly served as feeding medium. In general, the overall hydrolysis yield and lipid yield using fed-batch mode accounted for 93.2% and 97.6% of those using batch mode, respectively, resulting in a lipid output of 102.8 g/kg raw corn stover. The fatty acid composition and the prediction of biodiesel properties of lipid samples indicated the suitability for high-quality fuel production. This study provided valuable information for designing highly efficient lignocelluloses-to-biodiesel routes.

Highly sustainable cascade pretreatment of low-pressure steam heating and organic acid on pineapple waste biomass for efficient delignification

Cascade pretreatment of low-pressure steam heating (LPSH) and maleic acid (MA) on pineapple waste (PW) biomass aims to improve delignification, increase enzyme accessibility to carbohydrate in the feedstock while reducing inhibitor by-products. The best conditions for LPSH pretreatment were determined using one-factor-at-a-time (OFAT) while the conditions of MA pretreatment (temperature, acid concentration and time) were optimized by Box-Behnken design. A total of 68% (w/w) delignification with 79.5% (w/w) hemicellulose removal were achieved while 77.6% (w/w) cellulose was retained in the solid residue after the cascade pretreatment. No 5-hydroxylmethyl furfural (5-HMF) and acceptable furfural (1.8 g/L) were detected in the hydrolysate by high performance liquid chromatography analysis, with negligible amount of phenolic compounds (0.01 g/L). Compared to the pretreatment with combined LPSH and conventional sulphuric acid pretreatment (H2SO4), the pretreated PW produced 3.6 g/L of furfural and 0.4 g/L of HMF at similar optimized conditions. The pretreated PW were further characterized by scanning electron microscopy and Fourier transform infrared spectroscopy to analyze structural morphology and functional group changes. The pooled solid and liquid hydrolysate fractions generated from the LPSH and MA cascade pretreatment and subsequent enzyme hydrolysis has successfully generated 356.32 mg/g glucose and 156.91 mg/g xylose. The optimized cascade pretreatments provide up to 54.79% of glucose yield and 69.23% of xylose yield. Furthermore, 67.87% reduction of lignin content from the cascade pretreatment can substantially enhance the glucose yield up to 95.76% and xylose yield up to 99.07% during enzymatic hydrolysis using the mixture of cellulase and hemicellulase.

Inhibitor degradation by Rhodosporidium toruloides NRRL 1588 using undetoxified wood hydrolysate as a culture media

Lignocellulosic biomass has been identified as a renewable and sustainable feedstock to produce liquid hydrolysates as a suitable substrate to produce a variety of compounds through biochemical processes. Nevertheless, the main challenge to using this substrate is the hydrolysis needed to release fermentable sugars. This pretreatment leads to the production of microbial toxic compounds such as furans, phenols and organic acids. In this work, an oleaginous yeast, R. toruloides NRRL 1588, was used to study its ability to degrade inhibitors in C5 and C6 wood hydrolysates obtained from forestry residues. The study showed that R. toruloides NRRL 1588 can grow, accumulate lipids, and degrade up to 8.01 mgL−1 h−1 of furfural, 5.63 mgL−1 h−1 of 5-hydroxy methyl furfural, 1.70 mgL−1 h−1 of levulinic acid, 1.15 mgL−1 h−1 of syringaldehyde, 0.67 mgL−1 h−1 of vanillin, and 1.03 mgL−1 h−1 of vanillic acid. This work confirms the robustness of R. toruloides NRRL 1588 when grows in wood hydrolysates containing inhibitory compounds.

Process development for crystalline xylitol production from corncob biomass by Pichia caribbica

Xylitol, a commodity chemical, is widely used in nutraceutical and pharmaceutical formulations. Microbial xylitol production is a promising alternative to mitigate current industrial practice issues and offers an environment-friendly sustainable conversion route. This study demonstrates a bioprocess for xylitol production from corncob using a mesophilic yeast Pichia caribbica. Corncob was hydrolyzed by dilute acid and steam explosion to recover fermentable xylose and used as the feed for xylitol production. Activated carbon treatment (3% w/v) completely removed the biomass-derived inhibitors furfural and hydroxymethyl furfural from the liquid hydrolysate. The fermenting yeast Pichia caribbica produced 124.1 ± 0.45 g/L xylitol from the detoxified and concentrated corncob hydrolysate with a high yield of 0.80 ± 0.02 g/g. The crystallized xylitol with 96.5% purity demonstrated no harmful effects on the cell line used as a control for the in-vitro toxicity studies. This proof of concept can be applied to help scale up for bio-refinery-based large-scale production of xylitol from corncob biomass.

Modulation of aroma compounds in yeast and lactic acid bacterium co‐fermented pork hydrolysates by thermal treatment and addition of aroma precursors (cysteine and xylose)

SummaryThe objective of this study was to evaluate the effectiveness of using enzymatic hydrolysis and microbial fermentation coupled with thermal treatment methods in valorising a type of industrially generated meat by‐product: pork trimmings, so as to produce a value‐added meat‐based flavouring. The pork trimmings were first hydrolysed using a protease (Flavourzyme) under optimised conditions and then fermented into liquid hydrolysates with mixed Lactobacillus fermentum and Pichia kluyveri; afterwards, xylose and cysteine were added to the fermented hydrolysates for heat treatment. A characteristic “savoury and roasted‐meat” aroma was produced due to the formation of potent sulphur‐containing volatile compounds such as 2‐furfurylthiol and methionol, though the browning intensity was inhibited due to the presence of cysteine. The thermal treatment did not significantly affect the fruity and sweet‐smelling ester volatiles such as isoamyl acetate and hexyl acetate that resulted from microbial fermentation. The decreases of amino acids and xylose might be due to their active participation in the Maillard reaction. The produced pork hydrolysates that imparted a unique aroma could be applied as a flavour enhancer or seasoning in the food industry.

Dilute inorganic acid pretreatment of mixed residues of Cocos nucifera (coconut) for recovery of reducing sugar: optimization studies

Inorganic acids, such as sulphuric acid, hydrochloric acid, and nitric acid are widely used for the pretreatment of lignocellulosic biomass for bioenergy production. In this study, the effect of different acids on the recovery of reducing sugar from coconut residues (coir and pith) mixed in different ratios was studied. The pretreatment conditions for different acids were optimized using response surface methodology (RSM). The independent variables, such as biomass ratio, time and acid concentration were considered for the optimization studies with reducing sugar as the dependent variable. The maximum recovery of reducing sugar (45%) from mixed biomass was observed during nitric acid (NA) pretreatment. The recovery of reducing sugar was lower for hydrochloric acid (HA) and sulphuric acid (SA). The lower yield was attributed to the possible formation of sugar degradation compounds during acid pretreatment. Therefore, NA pretreatment was found suitable for mixed biomass compared to other acids. Further studies are required to understand the effect of NA pretreatment through a detailed study of liquid hydrolysate and the introduction of the saccharification process. Mixed biomass benefits the biorefinery industries for sustainable bioenergy production.