Changes in volatile profiles of a refrigerated-reheated xylose-cysteine-lecithin reaction model analyzed by GC×GC-MS and E-nose.

The changes in the volatile profiles of a xylose-cysteine-lecithin reaction model were investigated by using comprehensive two-dimensional gas chromatography-mass spectrometry (GC×GC-MS) in combination with headspace solid-phase microextraction (SPME) and electronic nose (E-nose) to evaluate the contribution of refrigerating and reheating treatment to warmed-over flavor (WOF). The volatile compound results and E-nose revealed that the contribution of refrigerating and reheating to the WOF was not consistent. After refrigerating, the level of furfuryl mercaptan increased, while that of 1-octene-3-ol, octanal, nonanal, and 2-decanone decreased, which affected the flavors. An increase in the level of 1-octene-3-ol, 2-pentyl-thiophene, and hexanoic acid and a decrease in the levels of furfural, 2-methyl-3-furanthiol, and 2-methyl-3-pentanethiol occurred during reheating. According to the odor activity value and sensory evaluation, the sulfur-like odor became more intense after refrigerating, while the rancid-like odor grew stronger, but the sulfur-like odor alleviated after reheating. Overall, the reaction between residual substances caused the WOF during refrigeration, also lead to the fatty acid oxidation increased after reheating. The overproduction of fatty acids oxidation products and decreased of volatile product of Maillard reaction leads to the WOF during reheating. PRACTICAL APPLICATION: This study provides theoretical guidance to reduce the off-flavors of meat products.

Deconstruction of banana peel for carbohydrate fractionation.

The deconstruction of banana peel for carbohydrate recovery was performed by sequential treatment (acid, alkaline, and enzymatic). The pretreatment with citric acid promoted the extraction of pectin, resulting in a yield of 8%. In addition, xylose and XOS, 348.5 and 17.3 mg/g xylan, respectively, were also quantified in acidic liquor as a result of partial depolymerization of hemicellulose. The spent solid was pretreated with alkaline solution (NaOH or KOH) for delignification and release of residual carbohydrates from the hemicellulose. The yields of xylose and arabinose (225.2 and 174.0 mg/g hemicellulose) were approximately 40% higher in the pretreatment with KOH, while pretreatment with NaOH promoted higher delignification (67%), XOS yield (32.6 mg/g xylan), and preservation of cellulosic fraction. Finally, the spent alkaline solid, rich in cellulose (76%), was treated enzymatically to release glucose, reaching the final concentration of 28.2 g/L. The mass balance showed that through sequential treatment, 9.9 g of xylose, 0.5 g of XOS, and 8.2 g of glucose were obtained from 100 g of raw banana peels, representing 65.8% and 46.5% conversion of hemicellulose and cellulose, respectively. The study of the fractionation of carbohydrates in banana peel proved to be a useful tool for valorization, mainly of the hemicellulose fraction for the production of XOS and xylose with high value applications in the food industry.

Composition, physicochemical properties, and anti-fatigue activity of water-soluble okra (Abelmoschus esculentus) stem pectins.

Okra, Abelmoschus esculentus (L.) Moench, an annual herbaceous plant, is widely distributed in tropical and subtropical regions. Water-soluble pectic hydrocolloids from okra stems (HOS) were extracted and purified using polydivinylbenzene HP-20 resins. The sugar composition of the purified HOS with an weight-average molecular weight of 178.4 ± 2.1 kDa and a polydispersity index of 1.02 ± 0.02 contained galacturonic acid (34%), galactose (31%), rhamnose (21%), arabinose (4.2%), glucuronic acid (2.5%), xylose (1.2%), and other monosaccharides (6.1%) by weight. Its favorable rheological behaviors were evident on relatively higher concentrations (20, 25, and 30 mg/mL) and moderately lower pH levels (3 and 5) of HOS. The anti-fatigue experiments in vivo demonstrated that a high dose of HOS (450 mg/kg feed) prolonged the exhaustive swimming time of mice, significantly induced an increase in blood glucose and glycogen, and decreased lactic acid and serum urea nitrogen levels. HOS digestion in vivo was fairly conducive to the improvement of energy storage capacity and renal function for physically induced fatigue, compared with the conventional herbal supplement Panax quinquefolium. Accordingly, HOS exhibits potential for reutilization of okra stem waste.

Immunoactive polysaccharides produced by heterotrophic mutant of green microalga Parachlorella kessleri HY1 (Chlorellaceae).

Hot water extract from biomass of heterotrophic mutant green alga Parachlorella kessleri HY1 (Chlorellaceae) was deproteinised, and three polysaccharidic fractions were obtained by preparative chromatography. The low-molecular fraction (1.5 × 104g mol-1) was defined mainly as branched O-2-ß-xylo-(1→3)-ß-galactofuranan where xylose is partially methylated at O-4. Two high-molecular fractions (3.05 × 105 and 9.84 × 104g mol-1) were complex polysaccharides containing α-l-rhamnan and xylogalactofuranan parts in different ratios. The polysaccharides were well soluble in hot water and, upon cooling, tended to self-segregate. Immunomodulatory activities of the obtained fractions were preliminary tested using ELISA, FACS and ImmunoSpot kits. The polysaccharides increased the TNF-α production in melanoma bearing mice with much higher intensity than in healthy mice. This was in agreement with the FACS results on T and B cells indicating their possibly secondary activation by innate immunity cells.

Recent catalytic routes for the preparation and the upgrading of biomass derived furfural and 5-hydroxymethylfurfural.

Furans represent one of the most important classes of intermediates in the conversion of non-edible lignocellulosic biomass into bio-based chemicals and fuels. At present, bio-furan derivatives are generally obtained from cellulose and hemicellulose fractions of biomass via the acid-catalyzed dehydration of their relative C6-C5 sugars and then converted into a wide range of products. Furfural (FUR) and 5-hydroxymethylfurfural (HMF) are surely the most used furan-based feedstocks since their chemical structure allows the preparation of various high-value-added chemicals. Among several well-established catalytic approaches, hydrogenation and oxygenation processes have been efficiently adopted for upgrading furans; however, harsh reaction conditions are generally required. In this review, we aim to discuss the conversion of biomass derived FUR and HMF through unconventional (transfer hydrogenation, photocatalytic and electrocatalytic) catalytic processes promoted by heterogeneous catalytic systems. The reaction conditions adopted, the chemical nature and the physico-chemical properties of the most employed heterogeneous systems in enhancing the catalytic activity and in driving the selectivity to desired products are presented and compared. At the same time, the latest results in the production of FUR and HMF through novel environmental friendly processes starting from lignocellulose as well as from wastes and by-products obtained in the processing of biomass are also overviewed.

Determination of chemical structure of pea pectin by using pectinolytic enzymes.

The chemical structure of pea pectin was delineated using pectin-degrading enzymes and biochemical methods. The molecular weight of the pea pectin preparation was 488,000, with 50 % arabinose content, and neutral sugar side chains attached to approximately 60 % of the rhamnose residues in rhamnogalacturonan-I (RG-I). Arabinan, an RG-I side chain, was highly branched, and the main chain was comprised of α-1,5-l-arabinan. Galactose and galactooligosaccharides were attached to approximately 35 % of the rhamnose residues in RG-I. Long chain ß-1,4-galactan was also present. The xylose substitution rate in xylogalacturonan (XGA) was 63 %. The molar ratio of RG-I/homogalacturonan (HG)/XGA in the backbone of the pea pectin was approximately 3:3:4. When considering neutral sugar side chain content (arabinose, galactose, and xylose), the molar ratio of RG-I/HG/XGA regions in the pea pectin was 7:1:2. These data will help understand the properties of pea pectin.

Improvement of the oxidative stability of cold-pressed sesame oil using products from the Maillard reaction of sesame enzymatically hydrolyzed protein and reducing sugars.

BACKGROUND: In recent years, cold-pressed oils have become more and more popular with consumers. However, their oxidative stability is low. Improving the oxidative stability of cold-pressed oils will increase their shelf life. Maillard reaction products (MRPs) have been shown to promote the oxidative stability of lipids. In this study, products from the Maillard reaction of reducing sugars and sesame enzymatically hydrolyzed protein (SEHP) were added to cold-pressed sesame oils to improve their oxidative stability. RESULTS: Three types of MRPs from reducing sugars (xylose, fructose, and glucose) and SEHP were prepared. Xylose-SEHP MRPs prepared under optimum conditions had the highest antioxidant activities among the three. The optimum conditions for xylose-SEHP were as follows: reaction temperature, 130 °C; reaction time, 180 min; pH, 6.5; and sugar/protein ratio, 10:1. The addition of xylose-SEHP MRPs at a level of 20 g kg-1 could significantly improve the oxidative stability of cold-pressed sesame oil. Besides, the addition of MRPs reduced the loss of tocopherol. The interaction of MRPs with endogenous antioxidants in the sesame oil (sesamol and tocopherol) was proved by comparison with lard. There was a synergistic increase in antioxidant activity for the combination of MRPs and sesamol and the combination of MRPs and tocopherol. CONCLUSIONS: The results provide evidence that adding certain MRPs can improve the oxidative stability of cold-pressed sesame oil. © 2019 Society of Chemical Industry.

Isolations, characterizations and bioactivities of polysaccharides from the seeds of three species Glycyrrhiza.

In this paper, polysaccharides from the seeds of three species of genus Glycyrrhiza were extracted to investigate the physicochemical properties, structural characteristics and antioxidant activities. The polysaccharides were composed of xylose, mannose, galactose, and glucose with different molar ratio. Fourier transform infrared spectroscopy showed the presence of key functional groups of polysaccharides whereas scanning electron microscopy analysis revealed the characteristic morphology of different polysaccharides, and thermogravimetric analysis exhibited good thermal stability of all samples. The antioxidant activities of polysaccharides were evaluated in vitro. All the three polysaccharides demonstrated strong reducing power, as well as scavenging activity against DPPH, ABTS, and hydroxyl free radicals. Antioxidant assays indicated that all the polysaccharides have obvious antioxidant activities and possess a potential development and application value in food, cosmetics as well as pharmaceutical industries.

Upgrade of wood sugar d-xylose to a value-added nutraceutical by in vitro metabolic engineering.

The upgrade of D-xylose, the most abundant pentose, to value-added biochemicals is economically important to next-generation biorefineries. myo-Inositol, as vitamin B8, has a six-carbon carbon-carbon ring. Here we designed an in vitro artificial NAD(P)-free 12-enzyme pathway that can effectively convert the five-carbon xylose to inositol involving xylose phosphorylation, carbon-carbon (C-C) rearrangement, C-C bond circulation, and dephosphorylation. The reaction conditions catalyzed by all thermostable enzymes from hyperthermophilic microorganisms Thermus thermophiles, Thermotoga maritima, and Archaeoglobus fulgidus were optimized in reaction temperature, buffer type and concentration, enzyme composition, Mg2+ concentration, and fed-batch addition of ATP. The 11-enzyme cocktail, whereas a fructose 1,6-bisphosphatase from T. maritima has another function of inositol monophosphatase, converted 20 mM xylose to 16.1 mM inositol with a conversion efficiency of 96.6% at 70 °C. Polyphosphate was found to replace ATP for xylulose phosphorylation due to broad substrate promiscuity of the T. maritima xylulokinase. The Tris-HCl buffer effectively mitigated the Maillard reaction at 70 °C or higher temperature. The co-production of value-added biochemicals, such as inositol, from wood sugar could greatly improve economics of new biorefineries, similar to oil refineries that make value-added plastic precursors to subsidize gasoline/diesel production.

Physicochemical properties of polysaccharides separated from Camellia oleifera Abel seed cake and its hypoglycemic activity on streptozotocin-induced diabetic mice.

Two homogeneous polysaccharide fractions named SCP-1 (7.16 × 106 Da) and SCP-2 (2.00 × 104 Da) were purified by DEAE-52 cellulose and Sephadex G-200 column chromatography successively from Camellia oleifera Abel seed cake. They were characterized by Fourier transformed infrared (FT-IR), high performance liquid chromatography (HPLC), nuclear magnetic resonance (NMR) spectroscopy and differential scanning calorimetry (DSC). The monosaccharide compositions of SCP-1 were d­mannose, d­glucose and l­xylose with a molar ratio of 1.77:0.93:1 and that of the SCP-2 were d­mannose, l­rhamnose, d­glucose and l­xylose with a molar ratio of 5.27:1.21:0.16:1. Animal experiments suggested that the plasma glucose levels in hyperglycemia mice were reduced by 11.34%, 30.70%, 46.83% after administration of high, medium and low doses of SCP-1, and reduced by 16.67%, 23.93% and 33.00% after administration of high, medium and low doses of SCP-2, respectively. SCP-1 and SCP-2 also increased the activities of glutathione peroxidase (GSH-Px), catalase (CAT) and superoxide dismutase (SOD), as well as decreased the content of malondialdehyde (MDA) in the hyperglycemia mice. These results suggested that SCP-1 and SCP-2 possessed strong hypoglycemic activities in streptozotocin-induced model mice. In addition, the hypoglycemic activity of SCP-1 was stronger than that of SCP-2.

Characterisation of pectin-xylan complexes in tomato primary plant cell walls.

The primary plant cell wall is composed of a complex network of pectin, hemicellulose and cellulose. Potential interactions between these polysaccharides were studied for carrot, tomato and strawberry, with a focus on the role of pectin. The Chelating agent Unextractable Solids (ChUS), the residue after water- and EDTA extraction, was ball milled and subsequently water extracted. For tomato and strawberry, pectin and substantial amounts of hemicellulose were solubilised. Anion exchange chromatography (AEC) showed co-elution of pectin and acetylated glucuronoxylan in tomato, representing 18% of solubilised uronic acid and 48% of solubilised xylose by ball milling from ChUS. The existence of a covalently linked pectin-xylan complex was proposed since xylan co-precipitated with pectin under mild alkali conditions. It was proposed that pectin links with xylan through the RG-I region since degradation of HG did not alter AEC elution patterns for RG-I and xylan, suggesting RG-I - xylan interactions.

Rheology and microstructure of gels based on wheat arabinoxylans enzymatically modified in arabinose to xylose ratio.

BACKGROUND: Arabinoxylans (AX) are polysaccharides consisting of a backbone of xyloses with arabinose substituents ester-linked to ferulic acid (FA). The arabinose to xylose ratio (A/X) in AX may vary from 0.3 to 1.1. AX form covalent gels by cross-linking of FA but physical interactions between AX chains also contribute to the network formation. The present study aimed to investigate the rheological and microstructural characteristics of gels based on AX enzymatically modified in A/X. RESULTS: Tailored AX presented A/X ranging from 0.68 to 0.51 and formed covalent gels. Dimers of FA content and elasticity (G') increased from 0.31 to 0.39 g kg-1 AX and from 106 to 164 Pa when the A/X in the polysaccharide decreased from 0.68 to 0.51. Atomic force microscopy images of AX gels showed a sponge-like microstructure at A/X = 0.68, whereas, at lower values, gels presented a more compact microstructure. Scanning electron microscopy analysis of AX gels show an arrangement of different morphology, passing from an imperfect honeycomb (A/X = 0.68) to a flake-like microstructure (A/X = 0.51). CONCLUSION: Lower A/X values favor the aggregation of AX chains resulting in an increase in di-FA content, which improves the rheological and microstructural characteristics of the gel formed. © 2017 Society of Chemical Industry.

Production of Chemicals by Klebsiella pneumoniae Using Bamboo Hydrolysate as Feedstock.

Bamboo is an important biomass, and bamboo hydrolysate is used by Klebsiella pneumoniae as a feedstock for chemical production. Here, bamboo powder was pretreated with NaOH and washed to a neutral pH. Cellulase was added to the pretreated bamboo powder to generate the hydrolysate, which contained 30 g/L glucose and 15 g/L xylose and was used as the carbon source to prepare a medium for chemical production. When cultured in microaerobic conditions, 12.7 g/L 2,3-butanediol was produced by wildtype K. pneumoniae. In aerobic conditions, 13.0 g/L R-acetoin was produced by the budC mutant of K. pneumoniae. A mixture of 25.5 g/L 2-ketogluconic acid and 13.6 g/L xylonic acid was produced by the budA mutant of K. pneumoniae in a two-stage, pH-controlled fermentation with high air supplementation. In the first stage of fermentation, the culture was maintained at a neutral pH; after cell growth, the fermentation proceeded to the second stage, during which the culture was allowed to become acidic.

One new flavonoid from Solanum rostratum.

One new flavonoid, 5,7,8,4'-tetrahydroxy-3-methoxyflavone-8-O-ß-d-xylopyranoside (2), along with other four known flavones (1, 3-5) were isolated from the aerial parts of Solanum rostratum. 8-hydroxyflavonoid was isolated from series Androceras for the first time. The structure of the new compound 2 was determined on the basis of spectroscopic techniques, including IR, NMR and HRESI-MS. The chemotaxonomic significance of these compounds was summarised.

Hybrid SSF/SHF Processing of SO2 Pretreated Wheat Straw-Tuning Co-fermentation by Yeast Inoculum Size and Hydrolysis Time.

Wheat straw is one of the main agricultural residues of interest for bioethanol production. This work examines conversion of steam-pretreated wheat straw (using SO2 as a catalyst) in a hybrid process consisting of a short enzymatic prehydrolysis step and a subsequent simultaneous saccharification and fermentation (SSF) step with a xylose-fermenting strain of Saccharomyces cerevisiae. A successful process requires a balanced design of reaction time and temperature in the prehydrolysis step and yeast inoculum size and temperature in the SSF step. The pretreated material obtained after steam pretreatment at 210 °C for 5 min using 2.5 % SO2 (based on moisture content) showed a very good enzymatic digestibility at 45 °C but clearly lower at 30 °C. Furthermore, the pretreatment liquid was found to be rather inhibitory to the yeast, partly due to a furfural content of more than 3 g/L. The effect of varying the yeast inoculum size in this medium was assessed, and at a yeast inoculum size of 4 g/L, a complete conversion of glucose and a 90 % conversion of xylose were obtained within 50 h. An ethanol yield (based on the glucan and xylan in the pretreated material) of 0.39 g/g was achieved for a process with this yeast inoculum size in a hybrid process (10 % water-insoluble solid (WIS)) with 4 h prehydrolysis time and a total process time of 96 h. The obtained xylose conversion was 95 %. A longer prehydrolysis time or a lower yeast inoculum size resulted in incomplete xylose conversion.

Novel sulfated xylogalactoarabinans from green seaweed Cladophora falklandica: Chemical structure and action on the fibrin network.

The water-soluble sulfated xylogalactoarabinans from green seaweed Cladophora falklandica are constituted by a backbone of 4-linked ß-l-arabinopyranose units partially sulfated mainly on C3 and also on C2. Besides, partial glycosylation mostly on C2 with single stubs of ß-d-xylopyranose, or single stubs of ß-d-galactofuranose or short chains comprising (1→5)- and/or (1→6)-linkages, was also found. These compounds showed anticoagulant activity, although much lower than that of heparin. The effect of a purified fraction (F1) on the fibrin network was studied in detail. It modifies the kinetics of fibrin formation, suggesting an impaired polymerization process. Scanning electron microscopy showed a laxer conformation, with larger interstitial pores than the control. Accordingly, this network was lysed more easily. These fibrin properties would reduce the time of permanence of the clot in the blood vessel, inducing a lesser thrombogenic state. One of the possible mechanisms of its anticoagulant effect is direct thrombin inhibition.

Purification, characterization and in vitro antioxidant activities of polysaccharide from Chaenomeles speciosa.

A water-soluble polysaccharide named as CSP-2 was isolated and purified from Chaenomeles speciosa by DEAE-Sepharose and Sephadex G-100 column chromatography. CSP-2 was composed of galactose (Gal), rhamnose (Rha), glucose (Glc) and xylose (Xyl) with a relative molar ratio of 3.8:1.6:1.2:0.4. The average molecular weight of CSP-2 was estimated to be about 4.6×104Da. The in vitro antioxidant assay showed that CSP-2 exhibited remarkable antioxidant activities to scavenge the DPPH radical, superoxide radical, hydroxyl radical and ABTS radical and significant cytoprotective effects on H2O2-induced PC12 cells injury in a concentration-dependent manner. Overall, CSP-2 may be useful as a naturally potential antioxidant agent for application in food and medicinal fields.

Structural characterization of sulfated arabinans extracted from Cladophora glomerata Kützing and their macrophage activation.

Water-soluble sulfated heteropolysaccharides were extracted from Cladophora glomerata Kützing and fractionated by ion-exchange chromatography, which yielded two subfractions, F1 and F2. The crude and fractionated polysaccharides (F1 and F2) mostly consisted of carbohydrates (62.8-74.5%) with various amounts of proteins (9.00-17.3%) and sulfates (16.5-23.5%), including different levels of arabinose (41.7-54.4%), galactose (13.5-39.0%), glucose (0.80-10.6%), xylose (6.84-13.4%), and rhamnose (0.20-2.83%). Based on the size exclusion chromatography (SEC) profiles, the crude and fractions mainly contained one peak with shoulders having molecular weight (Mw) ranges of 358-1,501 × 10(3). The F1 fraction stimulated RAW264.7 cells to produce considerable amounts of nitric oxide and cytokines compared to the crude and F2 fraction. The backbone of the most potent immunostimulating fraction (F1) was α-(1→4)-L-arabinopyranoside with galactose and xylose residues as branches at O-2 position, and sulfates mainly at O-2 position as well.

De Novo Transcriptome and Expression Profile Analysis to Reveal Genes and Pathways Potentially Involved in Cantharidin Biosynthesis in the Blister Beetle Mylabris cichorii.

The dried body of Mylabris cichorii is well-known Chinese traditional medicine. The sesquiterpenoid cantharidin, which is secreted mostly by adult male beetles, has recently been used as an anti-cancer drug. However, little is known about the mechanisms of cantharidin biosynthesis. Furthermore, there is currently no genomic or transcriptomic information for M. cichorii. In this study, we performed de novo assembly transcriptome of M. cichorii using the Illumina Hiseq2000. A single run produced 9.19 Gb of clean nucleotides comprising 29,247 sequences, including 23,739 annotated sequences (about 81%). We also constructed two expression profile libraries (20-25 day-old adult males and 20-25 day-old adult females) and discovered 2,465 significantly differentially-expressed genes. Putative genes and pathways involved in the biosynthesis of cantharidin were then characterized. We also found that cantharidin biosynthesis in M. cichorii might only occur via the mevalonate (MVA) pathway, not via the methylerythritol 4-phosphate/deoxyxylulose 5-phosphate (MEP/DOXP) pathway or a mixture of these. Besides, we considered that cantharidin biosynthesis might be related to the juvenile hormone (JH) biosynthesis or degradation. The results of transcriptome and expression profiling analysis provide a comprehensive sequence resource for M. cichorii that could facilitate the in-depth study of candidate genes and pathways involved in cantharidin biosynthesis, and may thus help to improve our understanding of the mechanisms of cantharidin biosynthesis in blister beetles.

Sequential Fenton oxidation and hydrothermal treatment to improve the effect of pretreatment and enzymatic hydrolysis on mixed hardwood.

Sequential Fenton oxidation (FO) and hydrothermal treatment were performed to improve the effect of pretreatment and enzymatic hydrolysis of mixed hardwood. The molar ratio of the Fenton reagent (FeSO4·7H2O and H2O2) was 1:25, and the reaction time was 96h. During the reaction, little or no weight loss of biomass was observed. The concentration of Fe(2+) was determined and was found to increase continuously during FO. Hydrothermal treatment at 190-210°C for 10-80min was performed following FO. Sequential FO and hydrothermal treatment showed positive effects on pretreatment and enzymatic hydrolysis. Xylose concentration in the hydrolysate was as high as 14.16g/L when FO-treated biomass was treated at 190°C, while its concentration in the raw material was 3.72g/L. After 96h of enzymatic hydrolysis, cellulose conversion in the biomass obtained following sequential treatment was 69.58-79.54%. In contrast, the conversion in the raw material (without FO) was 64.41-67.92%.