Characterization of xylan from rice bran and finger millet seed coat for functional food applications

First principles modelling of the ion binding capacity of finger millet

Finger millet, a cereal grain widely consumed in India and Africa, has gained more attention in recent years due to its high dietary fibre (arabinoxylan) and trace mineral content, and its climate resilience. The aim of this study was to understand the interactions between potassium (K+), calcium (Ca2+) and zinc (Zn2+) ions and the arabinoxylan structure and determine its ion-binding capacity. Three variations of a proposed model of the arabinoxylan structure were constructed and first principles Density Functional Theory calculations were carried out to determine the cation-binding capacity of the arabinoxylan complexes. Zn2+-arabinoxylan complexes were highly unstable and thermodynamically unfavourable in all three models. Ca2+ and K+ ions, however, form thermodynamically stable complexes, particularly involving two glucuronic acid residues as a binding pocket. Glucuronic acid residues are found to play a key role in stabilising the cation-arabinoxylan complex, and steric effects are more important to the stability than charge density. Our results highlight the most important structural features of the millet fibre regarding ion-storage capacity, and provide valuable preliminary data for confirmatory experimental studies and for the planning of clinical trials where the bioavailability of bound ions following digestion may be tested.

Self-assembly embedding of curcumin by alkylated rice bran protein

Lysine-rich rice bran protein (RBP) can be used as raw material for alkylation modification to improve the self-assembly performance of protein. The results of 1H NMR, degree of alkylation, and DSC analysis showed that the alkyl chain was successfully attached to the RBP. The surface hydrophobicity and absolute ζ-potential increased. The three-dimensional structure of the alkylated RBP (ARBP) become more porous and ARBP-2 was selected as the material for embedding curcumin. The XRD results revealed that curcumin induced self-aggregation of ARBP-2 and the inclusion of curcumin was attained. The maximum encapsulation efficiency of curcumin was 82.67 % and the maximum loading amount was 171.37 g/100 g RBP. The results of atomic force microscopy (AFM), particle size, and polydispersity index (PDI) analyses revealed that the particles in the system were aggregated after curcumin was added. Curcumin was well protected by encapsulation in the self-assembled particles. Thus, this study provides a new strategy for the embedding and delivery of curcumin.

Magnetic hydrogel based on xylan, poly (acrylic acid), and maghemite as adsorbent material for methylene blue adsorption: experimental design, kinetic, and isotherm

A magnetic hydrogel based on xylan (X), poly (acrylic acid), and maghemite (γ-Fe2O3) named HXA-Fe2O3 was synthesized, characterized, and applied as an alternative material to remove methylene blue (MB) from aqueous media by adsorption. Maghemite was synthesized by coprecipitation method and later incorporated in the hydrogel matrix synthesized by free radical polymerization. The characterization studies included FTIR, DSC, XRD, VSM, Zeta Potential, TGA, SEM, TEM, and N2 adsorption isotherms (BET). The physicochemical characterization results confirmed the intended synthesis and showed the compositional, thermal, structural, morphological, textural, and magnetic profile of the materials. The adsorption studies included experimental design, kinetic, and isotherm. A full factorial design was employed considering the factors adsorbent dosage (g L-1), pH, and ionic strength (mmol L-1 of NaCl) for adsorption capacity and removal percentage responses. As ionic strength was not significant, a Doehlert design was employed with adsorbent dosage and pH, indicating the optimal adsorption conditions. The kinetics was well described by the PSO model, while the isotherm obeyed the Sips model. Equilibrium was attained at 60 min, and the maximum experimental adsorption capacity was up to 250.26 mg g-1 at pH 8.5, adsorbent dosage of 0.2 g L-1, and 298 K. These findings show that the magnetic hydrogel produced has great potential to be applied in the adsorption of basic molecules, such as MB.

Physicochemical properties, phenolic content and in vitro digestion profile of Chinese black rice (Oryza sativa L.)

Yangxian black rice, as one of the ancient Chinese black rice varieties, is widely planted in the Yangxian area of China. This study investigated the physicochemical properties, phenolic content and in vitro digestion profile of Chinese black rice under gradient milling treatment. The chemical composition, color, pasting and thermal properties of black rice with different milling degrees were comprehensively compared. In vitro digestion analysis indicated that cooked rice flour had higher rapidly digestible starch (RDS) and lower resistant starch (RS) contents compared with the uncooked one. Besides, all cooked black rice samples exhibited high predicted glycemic index (pGI) value and whole black rice showed a lower pGI than refined rice. The microstructure and the abundance of phenolic compounds in the solid matrix during different treatments or digestion stages were observed by CLSM. Furthermore, a total of 102 phenolic constituents were absolutely quantified by targeted metabolomics techniques. Methanol extraction and moderate cooking treatment contributed to the release of phenolic compounds from the solid matrix of whole black rice. Besides, compared to the gastric digestion stage, the transition in the intestinal environment caused a decrease in the majority of the analyzed polyphenols. Identifying the phenolic constituents was favorable for a better elucidation of the chemical basis of the function and nutritional value of Chinese black rice.

Development of hydrogels based on xylan and poly (acrylic acid) for melamine adsorption in batch and continuous mode: experimental design, kinetics, isotherms, recyclability, and fixed-bed column

Two hydrogels were synthesized, characterized, and applied as alternative materials to remove melamine (MEL) from aqueous media by adsorption. For the first time, a complete study of MEL adsorption is presented, including optimization, kinetics, isotherm, reuse, and column studies with these new materials. One hydrogel is based on xylan and poly (acrylic acid) and was named HXy, and the other is based on the same components functionalized with activated carbon and was named HXy-AC. The materials were synthesized by free radical polymerization and characterized by FTIR, XRD, TGA, DSC, SEM, zeta potential, point of zero charge, N2 adsorption isotherms (BET), helium gas pycnometry, Archimedes method, swelling analysis, and stability tests. The characterization results confirmed the intended synthesis and showed the thermal, morphological, textural, structural, and compositional profile, as well as the adsorption characteristics of the materials. The adsorption studies in batch process included experimental design, kinetics, isotherms, and recyclability, and in continuous mode, the studies included fixed-bed column experiments. The full factorial design showed that adsorbent dosage, pH, and ionic strength are significant for adsorption capacity and removal percentage responses. Doehlert design enabled the definition of the values of adsorbent dosage and pH that were most suitable for MEL adsorption into the materials, indicating the optimal adsorption conditions. The kinetics were well described by the pseudo-first-order model, with R2 above 0.9920 for both materials at all concentrations tested. The isotherm obeyed the Langmuir model, with R2 above 0.9939 for both materials at all temperatures tested. Equilibrium was attained at 180 min, and the maximum experimental adsorption capacity was up to 132.46 and 118.96 mg g-1 at pH 7, with adsorbent dosage of 0.5 g L-1, and 298 K for HXy and HXy-AC, respectively. Furthermore, HXy and HXy-AC materials maintained about 58 and 70% of their initial adsorption capacity at the end of five adsorption/desorption cycles, respectively. Breakthrough curves were described by the Yan model and presented a maximum adsorption capacity of 30.2 and 30.4 mg g-1, treating 3.4 and 6.1 L of influent until the breakthrough point of 0.5 mg L-1 with HXy-AC using 2.0 and 4.0 g of material, respectively. These findings show that the hydrogels produced present the potential to be applied in the adsorption of basic molecules, such as MEL.

Synthesis of methylcellulose-polyvinyl alcohol composite, biopolymer film and thermostable enzymes from sugarcane bagasse

Agro-industrial wastes and by-products are the natural and abundant resources of biomaterials to obtain various value-added items such as biopolymer films, bio-composites and enzymes. This study presents a way to fractionate and to convert an agro-industrial residue, sugarcane bagasse (SB), into useful materials with potential applications. Initially cellulose was extracted from SB which was then converted into methylcellulose. The synthesized methylcellulose was characterized by scanning electron microscopy and FTIR. Biopolymer film was prepared by using methylcellulose, polyvinyl alcohol (PVA), glutaraldehyde, starch and glycerol. The biopolymer was characterized to exhibit 16.30 MPa tensile strength, 0.05 g/m² h of water vapor transmission rate, 366 % of water absorption to its original weight after 115 min of immersion, 59.08 % water solubility, 99.05 % moisture retention capability and 6.01 % of moisture absorption after 144 h. Furthermore, in vitro studies on absorption and dissolution of model drug by biopolymer showed 2.04 and 104.59 % of swelling ratio and equilibrium water content, respectively. Biocompatibility of the biopolymer was checked by using gelatin media and it was observed that swelling ratio was higher in initial 20 min of contact. The extracted hemicellulose and pectin from SB were fermented by a thermophilic bacterial strain, Neobacillus sedimentimangrovi UE25 that yielded 12.52 and 6.4 IU mL^-1 of xylanase and pectinase, respectively. These industrially important enzymes further augmented the utility of SB in this study. Therefore, this study emphasizes the possibility for industrial application of SB to form various products.

Xylans extracted from branches and leaves of Protium puncticulatum: antioxidant, cytotoxic, immunomodulatory, anticoagulant, antitumor, prebiotic activities and their structural characterization

This work aimed to isolate and characterize xylans from branches and leaves of Protium puncticulatum, in addition to evaluating its in vitro biological and prebiotic potential. The results showed that the chemical structure of the obtained polysaccharides is similar being classified as homoxylans. The xylans presented an amorphous structure, in addition to being thermally stable and presenting a molecular weight close to 36 g/mol. With regard to biological activities, it was observed that xylans were able to promote low antioxidant activity (< 50%) in the different assays evaluated. The xylans also showed no toxicity against normal cells, in addition to being able to stimulate cells of the immune system and showing promise as anticoagulant agents. In addition to presenting promising antitumor activity in vitro. In assays of emulsifying activity, xylans were able to emulsify lipids in percentages below 50%. Regarding in vitro prebiotic activity, xylans were able to stimulate and promote the growth of different probiotics. Therefore, this study, in addition to being a pioneer, contributes to the application of these polysaccharides in the biomedical and food areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03506-1.

Finger Millet Seed Coat-A Functional Nutrient-Rich Cereal By-Product

Finger millet (FM) is one of the little millets grown in Asia and Africa. Although still classified as an "orphan crop", there is an increasing interest in the research of FM seed coat (FMSC), also known as bran. It houses 90% of the seed's polyphenols and dietary fibre. The calcium and phosphorus content of FMSC is about 6- to 25-fold that of other cereals. FMSC is specifically beneficial for its polyphenols, arabinoxylans, phytates, and flavonoids content. Evidence of the hypoglycaemic, nephroprotective, hypocholesterolemic, and anti-cataractogenic effects of FMSC has been substantiated, thereby supporting the health claims and validating its nutraceutical potential for diabetics. This article discusses FMSC extraction and nutritional properties, focusing on arabinoxylan and polyphenols, their potential health benefits, and their application in food formulations. Although there is a dearth of information on using FMSC in food formulation, this review will be a data repository for further studies on FMSC.

Improvement of nutrient bioavailability in millets: Emphasis on the application of enzymes

Millets are a traditional staple food of the dryland regions of the world and are rich in essential nutrients like protein, fatty acids, minerals, vitamins, and dietary fiber. Also, millets commonly synthesize a range of secondary metabolites to protect themselves against adverse conditions. These factors are collectively termed anti-nutritional factors and the existence of these factors in millets might reduce the accessibility of the nutrients in humans. Some of these factors include protease inhibitors, tannins, non-starch polysaccharides-glucans, phytates, and oxalates each of which might directly or indirectly affect the digestibility of nutrients. Methods like soaking, germination, autoclaving, debranning, and the addition of exogenous enzymes have been used to reduce the anti-nutritional factors and elevate the bioavailability of the nutrients. This review summarizes various methods that have been used to improve nutrient bioavailability, specifically emphasizing the use of enzymes to improve nutrient bioavailability from millets. © 2021 Society of Chemical Industry.

Extraction and characterization of xylan from sugarcane tops as a potential commercial substrate

Xylan is the major hemicellulose present in sugarcane stem secondary cell walls. Xylan is composed of xylose backbone with a high degree of substitutions, which affects its properties. In the present study, the xylan from sugarcane tops (SCT) was extracted and characterized. Compositional analysis of xylan extracted from SCT (SCTx) displayed the presence of 74% of d-xylose residues, 16% of d-glucuronic acid residues and 10% of l-arabinose. High performance size exclusion chromatographic analysis of SCTx displayed a single peak corresponding to a molecular mass of ∼57 kDa. The Fourier transform infrared spectroscopic analysis of SCTx displayed the peaks corresponding to those obtained from commercial xylan. FESEM analysis of SCTx showed the granular and porous surface structure. Differential thermogravimetric analysis (DTG) of SCTx displayed two thermal degradation temperatures (T_d) of 228°C, due to breakdown of the side chains of glucuronic acid and arabinose and 275°C, due to breakdown of xylan back bone. The presence of arabinose and glucuronic acid as a side chains was confirmed by the DTG and thermogravimetric analysis. The CHNS analysis of SCTx showed the presence of only carbon and hydrogen supporting its purity. The recombinant xylanase (CtXyn11A) from Clostridium thermocellum displayed a specific activity of 1394 ± 51 U/mg with SCTx, which was higher than those with commercial xylans. The thin layer chromatography and electrospray ionization mass spectroscopy analyses of CtXyn11A hydrolysed SCTx contained a series of linear xylo-oligosaccharides ranging from degree of polymerization 2-6 and no substituted xylo-oligosaccharides because of the endolytic activity of enzyme. The extracted xylan from SCT can be used as an alternative commercial substrate and for oligo-saccharide production.

Acacia Xylan as a Substitute for Commercially Available Xylan and Its Application in the Production of Xylooligosaccharides

Over the past two decades, birchwood and beechwood xylans have been used as a popular substrate for the characterization of xylanases. Recently, major companies have discontinued their commercial production. Therefore, there is a need to find an alternative to these substrates. Xylan extraction from Acacia sawdust resulted in 23.5% (w/w) yield. The extracted xylan is composed of xylose and glucuronic acid residues in a molar ratio of 6:1 with a molecular mass of ∼70 kDa. The specific optical rotation analysis of extracted xylan displayed that it is composed of the d-form of xylose and glucuronic acid monomeric sugars. The nuclear magnetic resonance analysis of extracted xylan revealed that the xylan backbone is substituted with 4-O-methyl glucuronic acid at the O2 position. Fourier transform infrared analysis confirmed the absence of lignin contamination in the extracted xylan. Xylanase from Clostridium thermocellum displayed the enzyme activity of 1761 U/mg against extracted xylan, and the corresponding activity against beechwood xylan was 1556 U/mg, which confirmed that the extracted xylan could be used as an alternative substrate for the characterization of xylanases.

Effect of enzyme pretreatment in the ultrasound assisted extraction of finger millet polyphenols

Polyphenols from plant sources are increasingly recognized as functional ingredients with multiple health benefits. Finger millet (Eleusine coracana), a major millet grown in Asia and Africa is a significant source of polyphenols. The extraction of polyphenols from millets which are under-utilized has received less research attention compared to other plant matrices. Therefore, the present study was carried out to identify an effective method of extracting the polyphenols from finger millet (v. GPU 28) seed coat (FMSC). Two eco friendly methods namely ultrasonication (UA) and enzyme treatment followed by ultrasonication (EUA) were compared with the conventional heat reflux method (HR). The polyphenolic profile and content along with the antioxidant potential of the extract were evaluated. Phenolic yield increased 2.3 fold using EUA with xylanase (XUA) compared to heat reflux extraction (HR). However, yield with UA was equivalent to the conventional method. Total flavonoids increased 1.4 fold in UA and 1.3 fold in XUA, similarly, tannins also showed a significant increase (1.1 fold in UA and 1.2 fold in XUA). FTIR spectra revealed the presence of all phenolic functional groups and ESI-MS showed 80% similarity in the individual polyphenols in the extracts. Catechins, luteolin and cyanidin were identified in the UA and XUA treated samples, whereas, shikimic acid derivatives- caffeoyl and di caffeoyl were present only in XUA extracts. This is the first report on enhanced extraction of polyphenols from FMSC using a combination of enzyme treatment and ultrasonication, providing a green technology for utilization of polyphenols in nutraceuticals and functional foods.

Fractionation of DMSO-Extracted and NaOH-Extracted Hemicelluloses by Gradient Ethanol Precipitation from Neosinocalamus affinis

Neosinocalamus affinis hemicelluloses were extracted with pure DMSO and 3% NaOH in sequence. The DMSO- and NaOH-extracted hemicelluloses were then successively fractionated by gradient ethanol precipitation. NaOH-extracted hemicellulosic fractions with different branch degree could be separated by gradient ethanol precipitation, while DMSO-extracted hemicellulosic fractions could not. FT-IR spectra showed that DMSO-extracted fractions have more complete structure, while NaOH-extracted fractions have no acetyl at all. The FT-IR and NMR revealed that the DMSO-extracted Neosinocalamus affinis hemicelluloses were 4-O-methyl-glucuronoarabinoxylans consisting of a linear (1→4)-β-D-xylopyranosyl backbone with branches at O-2,3 of acetyl, O-2 of 4-O-methyl-a-D glucuronic acid, and O-3 of arabinose.