Quantification of glucose, xylose, arabinose, furfural, and HMF in corncob hydrolysate by HPLC-PDA-ELSD

Comparison of acid and hydrothermal pretreatments of date waste for value creation

The production of date syrup yields a substantial amount of date press cake (DPC), fibrous and moisturising material with great potential for generating value through bioprocessing. However, the recalcitrant structure of DPC affects the yield of products in bioprocesses. To boost the accessibility of the structure as well as increase the soluble fraction of carbohydrates and facilitate further enzymatic hydrolysis, hydrothermal and dilute acid (0.5% (v/v) sulfuric acid) pretreatments as cost-effective and feasible methods were applied on DPC at relatively low temperatures (80, 100, 120 and 140 °C) and reaction times (60 and 90 min). The success in pretreatment was then evaluated by a post-enzymatic treatment using an enzyme cocktail of cellulases and hemicelluloses. Based on total accessible sugar with minimum produced inhibitors, an optimal operating condition was considered acid pretreatment at 120 °C for 90 min with a 55.02% increase in total sugar yield. To explore the potential use of pretreated DPC, an anaerobic digestion was conducted on untreated and acid-pretreated DPC at 120 °C for 90 min. The results showed that pretreatment increased the total bioproduct yield, including hydrogen, ethanol, and volatile fatty acid yields, by 59.75%. This demonstrates the significant impact of pretreatment on product yields in a bioprocess.

A low-cost efficient online derivatization system for the determination of saccharides by high-performance liquid chromatograph-ultraviolet detector

In this study, a low-cost efficient online derivatization system was developed which allows for the detection of various types of mono- and oligo-saccharides only utilizing high-performance liquid chromatography (HPLC)-ultraviolet detector (UV) system. In the proposed method, phenylhydrazine was used as the derivatization reagent and directly spiked in the mobile phase, allowing for the separation and detection of mono- and oligosaccharides in an accessible instrument system (HPLC-UV). And the online derivatization design of the proposed method has significantly reduced the potential harm of derivatization reagents to the analysts. Furthermore, critical chromatographic parameters were optimized via the Box-Behnken design strategy, culminating in the ideal response for saccharides. Finally, the methodology validation of the proposed method was conducted. The proposed method showed satisfactory linear ranges with acceptable correlation coefficients (R2  > 0.99), outstanding accuracy (Recovery: 95.3%-105.6%), high intra-day precision (relative standard deviation [RSD]: 1.4%-7.1%) and inter-day precision (RSD: 2.0%-7.4%). The robustness and ruggedness of the proposed method were proved as the recovery values in the range of 95.0%-104.6% and 95.1%-104.8% for robustness and ruggedness, respectively. These satisfactory validation results confirm the applicability and reliability of the proposed method for the analysis of saccharides in various complex real-world samples.

Optimization of Textile Waste Blends of Cotton and PET by Enzymatic Hydrolysis with Reusable Chemical Pretreatment

Textile waste usually ends up in landfills and causes environmental pollution. In this study, pretreatment methods for textile recycling, including autoclaving, freezing alkali/urea soaking, and alkaline pretreatment, were applied to textile waste with various cotton/polyester blending ratios. The best condition for enzymatic hydrolysis was a 60/40 textile waste blend of cotton/polyethylene terephthalate (PET) with a reusable chemical pretreatment (15% NaOH) at 121 °C for 15 min. The hydrolysis of pretreated textile waste by cellulase was optimized using response surface methodology (RSM) based on central composite design (CCD). The optimized conditions were 30 FPU/g of enzyme loading and 7% of substrate loading, which resulted in a maximum observed value of hydrolysis yield at 89.7%, corresponding to the predicted value of 87.8% after 96 h of incubation. The findings of this study suggest an optimistic solution for textile waste recycling.

Opuntia ficus indica waste as a cost effective carbon source for lactic acid production by Lactobacillus plantarum

Opuntia ficus indica (OFI) waste was evaluated as a fermentation feedstock for lactic acid production using Lactobacillus plantarum. Dilute acid pretreatment of the OFI cladodes (OFIC) was performed for extracting maximum fermentable sugars by optimizing process parameters using statistical optimization method. The best results were obtained with HCl 1% (v/v), temperature 120 °C, residence time 40 min, granulation 350 µm and substrate loading 5% (w/v), the sugar concentration reached 24 g/L with low concentration of hydroxymethylfurfural. The feasibility of producing lactic acid from OFI fruit peel (OFIFP) as a source of carbon was also investigated. Lactobacillus plantarum was shown to have a capacity for lactic acid production from OFIC₃₅₀ (granulation 350 µm) hydrolysate and OFIFP extract without detoxification. The highest lactic acid yields of 0.46 and 0.78 g/g were obtained from enzymatic hydrolysate of pretreated OFIC₃₅₀ and OFIFP extract, respectively.

The occurrence and stability of Maillard reaction products in various traditional Chinese sauces

Traditional Chinese sauces, especially soy sauce, vinegar, and oyster sauce, provide foods with special color, flavor, and taste. However, during their manufacturing process, Maillard reaction products (MRPs) might be formed and cause adverse effects on human health. This study detected the levels of some typical MRPs in these sauces. Results showed that dark soy sauce and some vinegar products were high in 5-hydroxymethylfurfural (HMF). Moreover, dark soy sauce was significantly higher in 5-methylfurfural (MF) and methylglyoxal (MGO) than oyster sauce but lower in glyoxal (GO) than vinegar and oyster sauce, while light soy sauce had significantly higher advanced glycation end products (AGEs) than the rest three types of sauces. Besides, storage stability results indicated that MRPs increased obviously in vinegar and dark soy sauce. Finally, concentration limits/regulations of MRPs in traditional Chinese sauces should be established in the future considering their high frequency of usage and high potential of insalubrity.

Effects of hydrothermal pretreatment on the mono- and co-digestion of waste activated sludge and wheat straw

The refractory properties of waste activated sludge and wheat straw inhibit their bioenergy recovery by anaerobic digestion. This paper attempted to estimate the digestive performance, energy conversion efficiency and economic feasibility of wheat straw mono-digestion and its co-digestion with sludge by hydrothermal pretreatment at different temperature gradients (125, 150 and 175 °C). The results illustrated that the hydrolysis of both wheat straw and sludge were improved with the temperature increasing. It is noted that after pretreatment at 175 °C, wheat straw mono-digestion obtained the cumulative specific methane yield of 168.8 mL/g·VS, 6.9% reduction compared to the unpretreated straw (181.4 mL/g·VS) due to the inhibition by by-products (furfural and 5-hydroxymethylfurfural, 5-HMF) formed at high temperatures. The highest cumulative specific methane yield of 225.7 mL/g·VS was achieved by the co-digestion of pretreated wheat straw and pretreated sludge under 175 °C, indicating that the participation of sludge in co-digestion improved the buffer capacity of the system to relieve the inhibition. In addition, the co-digestion of sludge and wheat straw both pretreated at 175 °C obtained the maximum energy production of 7901.1 MJ/t, 52% promotion compared to the mono-digestion without pretreatment. The results of economic analysis showed that the mono-digestion of wheat straw obtained relatively low net profits and the mono-digestion of sludge pretreated at 175 °C achieved the highest net profit of 31.44 US$/t. These results suggest that the co-digestion of both pretreated wheat straw and sludge can achieve the highest biogas production and energy conversion efficiency.

Comparison of selective acidolysis of xylan and enzymatic hydrolysability of cellulose in various lignocellulosic materials by a novel xylonic acid catalysis method

An economically-prudent pretreatment is a crucial first step towards realization of the industrial lignocellulosic biorefinery. The aim of this study was to utilize lignocellulosic biomass to co-produce xylo-oligosaccharides (XOS) and glucose starting from a novel self-providing xylonic acid (XA) acidolysis method. Based on the optimization results of main acidolysis pretreatment parameters by uniform design experiments, we found that among various lignocellulosic materials, the highest yield of XOS from xylan was 54.16% with corncob, followed by 39.19% with wheat straw, 29.01% with corn straw and 30.23% with poplar sawdust. By effective degradation and removal of xylan constituents with XA acidolysis, enzymatic hydrolysabilities of inert cellulose constituents of corn cob, corn straw, wheat straw and poplar sawdust were achieved to 100%, 72.94%, 75.35% and 38.97%. Comparative mass balance diagrams of xylan and cellulose reveal that XA acidolysis pretreatment is environmental-friendly and effective for three agricultural residues, apart from woody poplar.

Pitfalls in the 3, 5-dinitrosalicylic acid (DNS) assay for the reducing sugars: Interference of furfural and 5-hydroxymethylfurfural

Transformation of renewable biomass into value-added chemicals and biofuels has evolved to be a vital field of research in recent years. Accurate estimation of reducing sugars post pretreatment of lignocellulosic biomass has been very inconsistent. For a few decades, 3,5-dinitrosalicylic acid (DNS) assay has been widely employed for the estimation of reducing sugars derived from pretreatment of lignocellulosic biomass. This assay tests for the presence of free carbonyl group (C=O), the so-called reducing sugars. This involves the oxidation of the aldehyde functional group present to the corresponding acid while DNS is simultaneously reduced to 3-amino-5-nitrosalicylic acid under alkaline conditions. However, the presence of other active carbonyl groups can potentially also react with DNS leading to incorrect yields of reducing sugars. Therefore, a detailed study has been carried out to evaluate the influence of active carbonyl compounds like furfural and 5-hydroxymethylfurfural (5-HMF) in the overall estimation of reducing sugars (glucose, xylose and arabinose) by DNS assay. In addition to this, reducing sugars estimation in the presence of furans were also investigated, it reveals that reducing sugars estimation was found to be 68% higher than actual sugars. Therefore, current findings strongly indicate that the employment of DNS assay for quantifying the reducing sugars in the presence of furans is not appropriate.

Quantification of morphochemical changes during in situ enzymatic hydrolysis of individual biomass particles based on autofluorescence imaging

Enzymatic hydrolysis of biomass is an established method for producing biofuels. Lignocellulosic biomass such as corn stover is very inhomogeneous material with big variation on conversion rates between individual particles therefore leading to variable recalcitrance results. In this study, we used noninvasive optical microscopy techniques, such as two-photon microscopy and fluorescence lifetime imaging microscopy, to visualize and analyze morphological and chemical changes of individual corn stover particles pretreated with sulfuric acid during hydrolysis. Morphochemical changes were interpreted based on the fluorescence properties of isolated building blocks of plant cell wall, such as cellulose, hemicellulose, and lignin. Enzymatic hydrolysis resulted in particle size reduction, side wall collapse, decrease of second harmonic signal from cellulose, redshifting of autofluorescence emission, and lifetime decrease attributed to the relative increase of lignin. Based on these observations, tracking compositional change after hydrolysis of individual particles was accomplished. The methodologies developed offer a paradigm for imaging and analyzing enzymatic hydrolysis in vitro and in situ, which could be used for screening enzymes cocktails targeting specific recalcitrant structures or investigating locally enzyme anti-inhibitory agents.

Core-shell gold-nickel nanostructures as highly selective and stable nonenzymatic glucose sensor for fermentation process

Non-enzymatic electrodes based on noble metals have excellent selectivity and high sensitivity in glucose detection but no such shortcomings as easy to be affected by pH, temperature, and toxic chemicals. Herein, spherical gold-nickel nanoparticles with a core-shell construction (Au@Ni) are prepared by oleylamine reduction of their metal precursors. At an appropriate Au/Ni ratio, the core-shell Au@Ni nanoparticles as a sensor for glucose detection combine the high electrocatalytic activity, good selectivity and biological compatibility of Au with the remarkable tolerance of Ni for chlorine ions (Cl-) and poisoning intermediates in catalytic oxidation of glucose. This electrode exhibits a low operating voltage of 0.10 V vs. SCE for glucose oxidation, leading to higher selectivity compared with other Au- and Ni-based sensors. The linear range for the glucose detection is from 0.5 mmol L-1 to 10 mmol L-1 with a rapid response time of ca. 3 s, good stability, sensitivity estimated to be 23.17 μA cm-2 mM-1, and a detection limit of 0.0157 mM. The sensor displays high anti-toxicity, and is not easily poisoned by the adsorption of Cl- in solution.

Biomass Pretreatment and Enzymatic Hydrolysis Dynamics Analysis Based on Particle Size Imaging

Parameters such as pretreatment method, enzyme type and concentration, determine the conversion efficiency of biomass' cellulose and hemicellulose to glucose and mainly xylose in biomass-based fuel production. Chemical quantification of these processes offers no information on the effect of enzymatic hydrolysis (EH) on particle morphology. We report on the development of a microscopy method for imaging pretreated biomass particles at different EH stages. The method was based on acquiring large field of view images, typically 20×10 mm2 containing thousands of particles. Morphology of particles with lengths between 2 μm and 5 mm could be visualized and analyzed. The particle length distribution of corn stover samples, pretreated with increasing amounts of sulfuric acid at different EH stages, was measured. Particle size was shown to be dependent on pretreatment severity and EH time. The methodology developed could offer an alternative method for characterization of EH of biomass for second generation biofuels and visualization of recalcitrant structures.

Rapid Determination of Acetic Acid, Furfural, and 5-Hydroxymethylfurfural in Biomass Hydrolysates Using Near-Infrared Spectroscopy

Near-infrared spectroscopy (NIRS) is a rapid detection technique that has been used to characterize biomass. The objective of this study was to develop suitable NIRS models to predict the acetic acid, furfural, and 5-hydroxymethylfurfural (HMF) contents in biomass hydrolysates. Using a uniform distribution of pretreatment conditions, 60 representative biomass hydrolysates were prepared. Partial least-squares regression was used to develop models capable of predicting acetic acid, furfural, and HMF contents. Optimal models were built using the wavenumber range of 9000-8000 and 7000-5000 cm^-1 with high R ² for calibration and validation models, small root-mean-square error of calibration (<0.21) and root-mean-square error of prediction (RMSEP, <0.42), and a ratio of the standard deviation of the reference values to the RMSEP of >2.7. The NIRS method largely reduced the analytical time from ∼55 to <1 min and has no cost for reagents.

The PWWP domain of the human oncogene WHSC1L1/NSD3 induces a metabolic shift toward fermentation

WHSC1L1/NSD3, one of the most aggressive human oncogenes, has two isoforms derived from alternative splicing. Overexpression of long or short NSD3 is capable of transforming a healthy into a cancer cell. NSD3s, the short isoform, contains only a PWWP domain, a histone methyl-lysine reader involved in epigenetic regulation of gene expression. With the aim of understanding the NSD3s PWWP domain role in tumorigenesis, we used Saccharomyces cerevisiae as an experimental model. We identified the yeast protein Pdp3 that contains a PWWP domain that closely resembles NSD3s PWWP. Our results indicate that the yeast protein Pdp3 and human NSD3s seem to play similar roles in energy metabolism, leading to a metabolic shift toward fermentation. The swapping domain experiments suggested that the PWWP domain of NSD3s functionally substitutes that of yeast Pdp3, whose W21 is essential for its metabolic function.

Dilute acid pretreatment of sorghum biomass to maximize the hemicellulose hydrolysis with minimized levels of fermentative inhibitors for bioethanol production

Conversion of lignocellulosic biomass into monomeric carbohydrates is economically beneficial and suitable for sustainable production of biofuels. Hydrolysis of lignocellulosic biomass using high acid concentration results in decomposition of sugars into fermentative inhibitors. Thus, the main aim of this work was to investigate the optimum hydrolysis conditions for sorghum brown midrib IS11861 biomass to maximize the pentose sugars yield with minimized levels of fermentative inhibitors at low acid concentrations. Process parameters investigated include sulfuric acid concentration (0.2-1 M), reaction time (30-120 min) and temperature (80-121 °C). At the optimum condition (0.2 M sulfuric acid, 121 °C and 120 min), 97.6% of hemicellulose was converted into xylobiose (18.02 mg/g), xylose (225.2 mg/g), arabinose (20.2 mg/g) with low concentration of furfural (4.6 mg/g). Furthermore, the process parameters were statistically optimized using response surface methodology based on central composite design. Due to the presence of low concentration of fermentative inhibitors, 78.6 and 82.8% of theoretical ethanol yield were attained during the fermentation of non-detoxified and detoxified hydrolyzates, respectively, using Pichia stipitis 3498 wild strain, in a techno-economical way.

Simultaneous determination of rhamnose, xylitol, arabitol, fructose, glucose, inositol, sucrose, maltose in jujube (Zizyphus jujube Mill.) extract: comparison of HPLC-ELSD, LC-ESI-MS/MS and GC-MS

Background

Jujube extract is commonly used as a food additive and flavoring. The sensory properties of the extract, especially sweetness, are a critical factor determining the product quality and therefore affecting consumer acceptability. Small molecular carbohydrates make major contribution to the sweetness of the jujube extract, and their types and contents in the extract have direct influence on quality of the product. So, an appropriate qualitative and quantitative method for determination of the carbohydrates is vitally important for quality control of the product.

Results

High performance liquid chromatography-evaporative light scattering detection (HPLC-ELSD), liquid chromatography-electronic spay ionization tandem mass spectrometry (LC-ESI-MS/MS), and gas chromatography–mass spectrometry (GC–MS) methods have been developed and applied to determining small molecular carbohydrates in jujube extract, respectively. Eight sugars and alditols were identified from the extract, including rhamnose, xylitol, arabitol, fructose, glucose, inositol, sucrose, and maltose. Comparisons were carried out to investigate the performance of the methods. Although the methods have been found to perform satisfactorily, only three sugars (fructose, glucose and inositol) could be detected by all these methods. Meanwhile, a similar quantitative result for the three sugars can be obtained by the methods.

Conclusions

Eight sugars and alditols in the jujube extract were determined by HPLC-ELSD, LC-ESI-MS/MS and GC–MS, respectively. The LC-ELSD method and the LC-ESI-MS/MS method with good precision and accuracy were suitable for quantitative analysis of carbohydrates in jujube extract; although the performance of the GC–MS method for quantitative analysis was inferior to the other methods, it has a wider scope in qualitative analysis. A multi-analysis technique should be adopted in order to obtain complete constituents of about the carbohydrates in jujube extract, and the methods should be employed according to the purpose of analysis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13065-016-0171-2) contains supplementary material, which is available to authorized users.

A Simple Analytical Method for High-Throughput Screening of Major Sugars from Soybean by Normal-Phase HPLC with Evaporative Light Scattering Detection

This paper presents a simple analytical method for determining sugars in soybean (Glycine max (L.) Merr.) tissues. Sample preparation was modified from several early published methods. High-performance liquid chromatography (HPLC) equipped with an evaporative light scattering detector (ELSD) was used to separate, identify, and quantify seven sugars, including glucose, galactose, fructose, sucrose, melibiose, raffinose, and stachyose. Two mobile phases were programed into a gradient elution. Mobile phase A is pure water and mobile phase B is a mixture of acetonitrile and acetone 75 : 25 (v/v). Total chromatographic retention time is less than 20 minutes. This method has been validated for detection limit, calibration range, and intraday and interday repeatability. This method has been used analyzing more than 5000 soybean samples in the experiments studying natural genetic variation of sugar contents and components in soybean seeds and other tissues.

Improved evaporative light scattering detection for carbohydrate analysis

Optimization and validation of evaporative light scattering detector (ELSD), aided by response surface methodology (RSM), has been developed for the liquid chromatography analysis of a wide molecular weight (MW) range of carbohydrates, including polysaccharides and oligosaccharides. Optimal experimental parameters for the ELSD detection were: 88.8°C evaporator temperature, 77.9°C nebulizer temperature and 1.1 standard litres per minute nitrogen flow rate. Optimal ELSD detection, used together with high performance size exclusion chromatography (HPSEC) of carbohydrates, gave a linear range from 250 to 1000 mg L(-1) (R(2)>0.998), with limits of detection and quantitation of 4.83-11.67 and 16.11-38.91 mg L(-1), respectively. Relative standard deviation was lower than 1.8% for intra-day and inter-day repeatability for apple pectin, inulin, verbascose, stachyose and raffinose. Recovery ranged from 103.7% to 118.3% for fructo-oligosaccharides, α-galacto-oligosaccharides and disaccharides. Optimized and validated ELSD detection is proposed for the analysis of high- to low-MW carbohydrates with high sensitivity, precision and accuracy.