Molecular Weight Distribution Research Articles

Low‐Dispersity Polymers via Free Radical Alternating Copolymerization: Effects of Charge‐Transfer‐Complexes

AbstractAlternating copolymers are crucial for diverse applications. While dispersity (Ð, also known as molecular weight distribution, MWD) influences the properties of polymers, achieving low dispersities in alternating copolymers poses a notable challenge via free radical polymerizations (FRPs). In this work, we demonstrated an unexpected discovery that dispersities are affected by the participation of charge transfer complexes (CTCs) formed between monomer pairs during free radical alternating copolymerization, which have inspired the successful synthesis of various alternating copolymers with low dispersities (>30 examples, Ð=1.13–1.39) under visible‐light irradiation. The synthetic method is compatible with binary, ternary and quaternary alternating copolymerizations and is expandable for both fluorinated and non‐fluorinated monomer pairs. DFT calculations combined with model experiments indicated that CTC‐absent reaction exhibits higher propagation rates and affords fewer radical terminations, which could contribute to low dispersities. Based on the integration of Monte Carlo simulation and Bayesian optimization, we established the relationship map between FRP parameter space and dispersity, further suggested the correlation between low dispersities and higher propagation rates. Our research sheds light on dispersity control via FRPs and creates a novel platform to investigate polymer dispersity through machine learning.

Influence of fractions with different molecular weight distributions from high-amylose starches on their digestibility after recrystallization

Type 3 resistant starches (RS3) were prepared from debranched starch (DBS) with different average degree of polymerization (DP) generated from high-amylose pea starch (HAPS) and high-amylose maize starch (HAMS). The results showed that RS3 with DP 35 and DP 39 had the highest RS content (74.5 % and 75.0 %, respectively) after cooking, which were remarkably higher than those of RS3 prepared from mixed fractions (60.6 % and 49.0 %, respectively) and other separated fractions (34.1–63.0 %). The multi-scale structures of RS3, including short-range molecular order, crystalline structure, micro-ordered aggregate structure, microscopic structure, and particle size distribution, were influenced by the average DP. Notably, RS content was positively correlated with the proportion of DP 51–80 and negatively correlated with the proportion of DP 21–30. DBS with DP 51–80 contributed to a more organized micro-ordered aggregate structure at nanometer scale and a larger aggregate structure at micrometer scale, which improved the resistance of RS3 to amylolytic enzymes. However, DBS with DP 21–30 tended to form random coil structure that were more easily to be digested. This research offered new insights into the structure-digestibility relationship of RS3, which is meaningful for the development of RS3 with high resistance to amylolytic enzymes after cooking.

Multi-functional RAFT reagent to prepare fluorescent hyper-branched macromolecular probes for the detection of Fe3+ ions

Reversible addition-fragmentation chain transfer (RAFT) polymerization has the advantages of precise control, high yield, and narrow molecular weight distribution. These merits make it an ideal method for the preparation of hyper-branched fluorescent polymers (FL-HBPs). In this work, a multi-functional RAFT reagent (AVCT-NLP) was prepared for the synthesis of monodisperse FL-HBPs. Firstly, dithionate compound (CN1) containing a CC double bond was synthesized by the reaction of 4-nitrophenol with 1-(bromomethyl)-4-vinylbenzene. Subsequently, the NO2 group on CN1 was reduced to NH2, and the −Br on the 4-bromo-1,8-naphthalic anhydride was substituted to emit fluorescence. Finally, the fluorophore was introduced by the reaction of NH2 with the anhydride on the naphthalene ring to obtain AVCT-NLP which contains fluorophore, dithionate, and CC double bond in one molecule. AVCT-NLP was then used to synthesize the homopolymer (PAVCT-NLP) as both monomer and RAFT reagent. Moreover, PAVCT-NLP served as a macromolecular RAFT reagent, and hydrophilic monomer methacrylic acid (MAA) or 3-butene-1,2-diol were polymerized to obtain amphiphilic hyper-branched polymers (FL-AHBP-1, FL-AHBP-2). All the as-prepared macromolecules (PAVCT-NLP, FL-AHBP-1, and FL-AHBP-2) exhibited specific recognition and high sensitivity for Fe3+. The fluorescence quenching reached up to 74.4 %, with the limit of detection (LOD) as low as 1.82 nM. Additionally, the probe demonstrated pH stability and environmental adaptability. Due to the multi-functional structures of AVCT-NLP, it could be subjected to RAFT polymerization to obtain a monodisperse hyper-branched polymer. All polymers have a high fluorophore density and the polydispersity index (PDI) of the polymer is close to 1.00. This paper provided an effective approach for synthesizing polymer fluorescent probes with versatile structure and fluorescence properties in future applications.

Investigation of the Influence of UV Radiation on Compositions of Polylactide with Graphite Nanoplates

Composites of polyether polylactide (PLA) synthesized from natural raw materials with graphite nanoplates (GNP), which represent a new type of composite materials based on biodegradable polymers, were obtained by solid-phase method under the action of shear deformations. The porosity of composites was evaluated and their electrical and mechanical properties were studied. The effect of UV radiation on the molecular weight and molecular weight distribution of PLA in PLA-GNP composites of different compositions was investigated using the method of excision chromatography (EC), and the effect of the GNP nanofiller content on the change of their mechanical characteristics in the process of radiation was shown.

A rigorous model for hydrogen response in industrial propylene polymerization loop reactors: From micro-mechanism to macro-behavior

In spite of playing a chain transfer agent role, the hydrogen activation effect in propylene polymerization with Ti-based Ziegler-Natta catalysts, so called “hydrogen response”, is usually explained by the dormant-site theory in polymer chemistry. However, how the micro-mechanism at the catalyst site scale affects the macro-behavior of industrial processes is unrevealed. This work aims at developing a rigorous model that can accurately describe hydrogen response and predict polymer chain microstructure for an industrial propylene polymerization process consisting of loop reactors in series. The model is comprised of a kinetic model, a thermodynamic model, and a macroscopic non-ideal loop reactor model. To describe hydrogen response, an elaborated kinetic model is established based on a consistent dormant site reactivation mechanism assuming a multi-site model. The model predictions are in good agreement with plant data, after taking the dormant sites reactivated by hydrogen into account. The proposed model is capable of fully assessing the effects of various process conditions, during steady-state and grade transition processes, on the macro-behavior (i.e., production, slurry density) as well as polymer properties (i.e., melt flow index, molecular weight distribution) in the industrial loop reactors. The underlying correlations are also discussed.

Aromatic (co)polycarbonates bearing pendant 2,3-dimethylmaleimido group based upon a new phthalimidine-containing “cardo” bisphenol

A new “cardo” bisphenol viz., 1-(2-(1,1-bis(4-hydroxyphenyl)-3-oxoisoindolin-2-yl)ethyl)-3,4-dimethyl-1H-pyrrole-2,5-dione (PPH-MA) was synthesized in a two-step reaction sequence starting from phenolphthalein. PPH-MA was utilized as a step-growth monomer for the synthesis of a homo- and fourco-polycarbonates bearing pendant 2,3-dimethylmaleimido groups (PC-MAs) via solution polycondensation of PPH-MA or various mol % compositions of PPH-MA and bisphenol-A, respectively, with triphosgene.1H NMR spectroscopy confirmed the chemical structure and composition of PC-MAs. Inherent viscosity and number average molecular weight values of PC-MAs were in the range 0.45–0.64 dL g−1 and 18,300 − 36,200 g mol−1, respectively, indicating the formation of polymers of medium to reasonably high molecular weights. Tough, transparent and flexible films of PC-MAs could be cast from chloroform solution. X-ray diffraction studies indicated the amorphous nature of PC-MAs. The 10% weight loss temperature (T10) values of PC-MAs were in the range 373–443 °C indicating their good thermal stability.

Synthesis of linear low-density polyethylene waxes through chain-walking benzocycloalkyl nickel-catalyzed ethylene polymerization

Polyethylene wax is a highly useful material, and its diverse topological structures may have a significant impact on its applications. In this study, we have devised and synthesized a series of unilateral benzocycloalkyl α-diimine nickel catalysts. These nickel catalysts exhibited very high activities (1.06 to 10.25 × 106 g mol-1·h-1) and yielded branched (37–97/1000 C) polyethylene waxes with low molecular weights (Mn = 0.49 to 2.01 kg mol-1) and variable molecular weight distributions (1.79–35.05) in ethylene polymerization. Polymerization conditions such as pressure and temperature and catalyst structure such as backbone and axial substituents have an important influence on the polymerization activity and the properties of the resulting polyethylene waxes. High-temperature NMR reveals that these branched polyethylenes primarily feature short-chain branches, such as the methyl group, and exhibit a topology resembling that of low-molecular-weight linear low-density polyethylene (LLDPE).

Enhancing Molar Mass Distributions of Lignosulfonates with Chemometry-Assisted Functional Group Profiling

Enhancing Molar Mass Distributions of Lignosulfonates with Chemometry-Assisted Functional Group Profiling

Hyaluronic Acid Influences Amino Acid Metabolism via Differential L‐Type Amino Acid Transporter 1 Expression in the U87‐Malignant Glioma Cell Line

The glioblastoma (GBM) tumor microenvironment is heterogeneous, complex, and being increasingly understood as a significant contributor to tumor progression. In brain tumors, the extracellular matrix contains a large concentration of hyaluronic acid (HA) that makes it important to study its role in cancer progression. In particular, abnormal accumulation of HA is observed in gliomas and is often associated with poor prognosis. In addition, HA is a polymer and its molecular weight (MW) distribution may influence tumor cell activity. Herein, the influence of the MW of HA on tumor cell metabolism is evaluated. A 2D cell culture approach is used to expose the U87‐MG (medium glucose [MG]) cell line to different HA MWs (10, 60, and 500 kDa) and glucose concentrations (0, 5.5, and 25 mm). Notably, it is found that HA influences GBM amino acid metabolism via reduction in LAT1 transporter protein expression. Also an influence on mitochondrial respiration levels and a difference in the accumulation of some key products of cell metabolic activity (lactic acid, glutamic acid, and succinic acid) are reported. Overall, in these results, it is indicated that HA MW can influence GBM metabolic state, with implications for cell invasion and tumor progression.

Characterization and structure-functionality analysis of starch in different layers of Lycoris chinensis bulb scales

According to literature, the size distribution of starch granules varies significantly in different layers of Lycoris chinensis bulb scales, however its effect on structural and physicochemical properties of starch still remains unclear. In this study, outer, middle and inner layers of bulb scales of L. chinensis were compared for starch characteristics. Also, the structure-functionality association was investigated based on correlation analysis and hierarchical cluster analysis, using 37 starch quality traits. Compared to commonly consumed starches with similar amylose content, L. chinensis starch gel had lower hardness and viscosities. Among layers, starches varied significantly in particle size, physicochemical and structural properties. As compared to middle and inner scales, the starch in outer scales had higher amylose content, hardness and viscosities, but lower gelatinization temperature, weight-average molar mass and degree of polymorphism. Correlation analysis revealed significant correlations among traits, and interestingly, gelatinization temperature (Tp) was found positively correlated to traits of molecular weight (p < 0.05). The 37 traits of starch characteristics can be divided into three subgroups, as supported by the results of Pearson correlation analysis and hierarchical cluster analysis. In general, the information presented in the current study are useful for Lycoris bulb starch utilization and insightful for a better understanding of structure-functionality association of starch.

RELAXATION BEHAVIOR OF 3D PRINTED NBR-BASED RUBBER O-RINGS AS THE INNER PART OF ROD SEALS

ABSTRACT The viscoelastic properties of rubber polymer–based compounds are crucial for further applications but challenging in the manufacturing process using additive manufacturing techniques. The fact that the first layer is attached to the printing bed restricts free relaxation after extrusion and the part shows a strong contraction along the printing direction after release and especially after vulcanization. In this study, the molar mass distribution and the acrylonitrile (ACN) content of an NBR-based compound for the fabrication of O-rings for rod seal applications were varied to demonstrate the different degree of contraction resulting from three-dimensional printing. An ACN content of 34% and an average molar mass of 2.47·105 g·mol−1 with a dispersity index of 2.6 was found to be a suitable compromise between the degree of contraction and compression set as a criterion for the application as O-ring as the inner part of rod seals.

Evaluation of Grafting Parameters of Styrene onto Alkaline Modified Sugarcane Bagasse using Fe2+/H2O2 and Fe2+/H2O2-N2H4 initiator systems and Characterization of the Hydrolyzed Grafted Polystyrene Chains

Cellulose the most abundant natural fibre can be modified, via grafting with vinyl monomers, in homogenous or heterogeneous reaction medium. Therefore, the objective of this paper was to study the grafting parameters of styrene onto alkaline modified sugarcane bagasse using Fe2+/H2O2 and Fe2+/H2O2- N2H4 initiator systems and characterized the hydrolyzed grafted polystyrene chains for their viscometry and average molecular weight distributions using standard appropriate methods. The grafting parameters increases within 0.10-0.25 M styrene concentration in both initiator systems and initiator concentration within the range 1.0x10-3 to 6.0x10-3 for Fe2+/H2O2- N2H4 and 1.0x10-3 to 9.0x10-3 for Fe2+/H2O2 systems, albeit with higher values in the former system. These parameters decrease at higher monomer and initiator concentrations in both systems. The viscometry of hydrolyzed polystyrene chain prepared at optimum initiator concentrations and 0.10-0.30 M styrene concentration in both initiator systems are in the range (1.6416-4.5327 cP), (0.6416-3.5327 cP) and (73.2277-202.1927 cP) for relative, specific and inherent viscosities respectively, consistent with increases in activation energy of flow (1.24-5.30 KJmol-1) and average viscosity molecular weights (307.92-565.79 gmol-1) , these parameters decreases at higher monomer concentration in both initiator systems. The number and weight-average molecular weight distributions and polydispersity indices indicates that grafted polystyrene chains in Fe2+/H2O2 system are broader and more polydispersed than those for Fe2+/H2O2- N2H4 initiator system. The results showed that the hydrazine enhanced initiator system was more effective for the copolymerization reaction with polystyrene polydispersity indices comparable to those of synthetic chain-growth polymers.

Effects of Protein on Green Tea Quality in a Milk-Tea Model during Heat Treatment: Antioxidant Activity, Foaming Properties, and Unbound Small-molecule Metabolome

Tea drinks/beverage has a long history and milk is often added to enhance its taste and nutritional value, whereas the interaction between the tea bioactive compounds with proteins has not been systematically investigated. In this study, a milk-tea model was prepared by mixing green tea solution with milk and then heated at 100°C for 15 min. The milk tea was then measured using biochemical assay, antioxidant detection kit, microscopy as well as HPLC-QTOF-MS/MS after ultrafiltration. The study found that as the concentration of milk protein increased in the milk-tea system, the total phenol-protein binding rate raised from 19.63% to 51.08%, which led to a decrease in free polyphenol content. This decrease of polyphenol was also revealed in the antioxidant capacity, including 2,2-diphenyl-1-picrylhydrazyl radical scavenging ability and ferric ion reducing antioxidant power, in a dose-dependent manner. Untargeted metabolomics results revealed that the majority of small-molecule compounds/polyphenols in tea, such as epigallocatechin gallate, (-)-epicatechin gallate, and Catechin 5,7,-di-O-gallate, bound to milk proteins and were removed by ultrafiltration after addition of milk and heat treatment. The SDS-PAGE and Native-PAGE results further indicated that small molecule compounds in tea formed covalent and non-covalent complexes by binding to milk proteins. All above results partially explained that milk proteins form conjugates with tea small-molecule compounds. Consistently, the particle size of the tea-milk system increased as the tea concentration increased, but the polymer dispersity index decreased, indicating a more uniform molecular weight distribution of the particles in the system. Addition of milk protein enhanced foam ability in the milk-tea system but reduced foam stability. In summary, our findings suggest that the proportion of milk added to tea infusion needs to be considered to maintain the quality of milk-tea from multiple perspectives, including stability, nutritional quality and antioxidant activity.

Structural analysis and biological activity of cell wall polysaccharides and enzyme-extracted polysaccharides from pomelo (Citrus maxima (Burm.) Merr.)

Pomelo peel is a valuable source of pectin, but research on its cell wall polysaccharides is limited. This study compared the cell wall polysaccharides of pomelo peel, enzyme-extracted polysaccharides of pomelo peel, and enzyme-extracted polysaccharides of whole pomelo fruit. Cell wall polysaccharides, including water-soluble pectin (WSP), chelator-soluble pectin (CSP), sodium carbonate-soluble pectin (NSP), 1 mol/L KOH soluble hemicellulose (KSH-1), and 4 mol/L KOH soluble hemicellulose (KSH-2), were obtained by sequence-extraction method. Total polysaccharides from whole pomelo fruit (TP) and peel-polysaccharides from pomelo pericarps (PP) were obtained using enzyme-extraction method. The structural, thermal, rheological, antioxidant properties, and wound healing effect in vitro were described for each polysaccharide. WSP had a uniform molecular weight distribution and high uronic acid (UA) content, suitable for commercial pectin. NSP had the highest Rhamnose (Rha)/UA ratio and a rich side chain with highest viscosity and water retention. PP displayed the highest DPPH radical scavenging activity and reducing capacity at 0.1 to 2.0 mg/mL concentration range, with an IC50 of 1.05 mg/mL for DPPH free radicals. NSP also demonstrated the highest hydroxyl radical scavenging activity and promoted Human dermal keratinocyte proliferation and migration at 10 μg/mL, suggesting potential applications in daily chemical and pharmaceutical industries.

Evaluating the operational properties of concrete admixtures containing molecularly modified polycarboxylate superplasticizers

The objective of this study focused on the design and preparation of a molecularly modified polycarboxylate superplasticizer to develop concretes with enhanced engineering features. For this purpose, polyethylene glycol was chemically modified with maleic anhydride to give the mono polyethylene glycol maleate (MPEGM). Then, polycarboxylate superplasticizer comprising of isoprenyl oxy polyethylene glycol (TPEG) and acrylic acid (AA, PCE-1), and the synthesized MPEGM with TPEG and AA (PCE-2) were prepared through solution radical polymerization. Subsequently, concrete mixtures with different dosages (0, 0.1, 0.15, 0.2, 0.25, 0.3 wt%) of PCE-1 and PCE-2 were prepared. Chemical structure of the synthesized MPEGM and superplasticizers together with their copolymer composition were identified by FTIR and 1HNMR analyses. The molecular weights (Mw) and molecular weight distributions (PDI) of PCE-1 (8.74 × 104, 1.36) and PCE-2 (8.74 × 104, 2.19) were studied by GPC analysis, respectively. The zeta potential of cement particles (2.8 mV) becomes negative in the presence of 0.6 g/L of PCE-1 (− 7.8) and PCE-2 (− 9.5). This implies that electrostatic and steric hindrance forces of adsorbed superplasticizers synergistically provide a situation for appropriate dispersion of cement particles. The results of water-reducing percentage, fluidity, air content, bleeding water rate, initial and final setting times, wet density, flexural and compressive properties, and ultrasonic pulse velocity analyses exhibit significant enhancement on the features of concrete mixtures made of polycarboxylate superplasticizer. The superiority of PCE-2 to PCE-1 was connected to its adsorption-dispersibility potent induced by stronger electrostatic and steric repulsion forces, which result in quality and continuity enhancement in concretes.

In vitro and in vivo effects of pectin‐type polysaccharides isolated from crabapples (Malus prunifolia) on inflammatory colitis models

SummaryThe aim of this study was to investigate the anti‐inflammatory effects of polysaccharides extracted from crabapples (Malus prunifolia; MP) in vitro and in vivo. Crabapples were subjected to hot water extraction to obtain MP‐HW, which was further separated into low (MP‐L) and high molecular weight (MW) (crude polysaccharide; MP‐CP) fractions by ethanol precipitation. Based on MW distribution, general composition, component sugars, and Fourier transform infrared spectroscopy, MP‐CP was identified as a pectin‐type polysaccharide rich in galacturonic acid with an MW of 106.2 kDa. MP‐CP inhibited the production and mRNA expression of proinflammatory factors in an IL‐1β‐treated intestinal epithelial cell model. In addition, MP‐CP significantly alleviated the body weight, disease activity index score, colon length, and spleen weight in mice with dextran sulfate sodium (DSS)‐induced colitis. The MP‐CP‐treated group showed effective regulation of the expression of pro‐ and anti‐inflammatory factors and immunoglobulin A than the DSS‐treated group. Haematoxylin and eosin and Alcian blue staining revealed that MP‐CP alleviated inflammatory manifestations and mucin expression in the intestinal lumen. Collectively, pectin‐type polysaccharides isolated from crabapples may be used as a new functional food and pharmaceutical agent for the prevention and treatment of inflammatory colitis.

Impact of Pretreatment With Acid and Ultrasound on the Production and Characteristics of Goat Skin Gelatin

Goat skin is a potential raw material source for gelatin production using acid-ultrasound pretreatment. The objective of this study was to investigate the use of ultrasound in combination with acid pretreatment for the preparation of goat skin gelatin. Gelatin was extracted from goat skin using different pretreatments: acetic acid (T1), acetic acid followed by ultrasound (20 kHz and 750 W) (T2), and without pretreatment (T0). The results showed that the combination of acetic acid and ultrasound pretreatment significantly impacted the quality of the resulting gelatin. The study results showed an increase in yield (9.24 to 25.48%), hydroxyproline content (102.07 to 231.31 mg/g), gel strength (4.76 to 197.62 g), viscosity (6.80 to 48.00 cP), melting point (32.47 to 35.85 oC), EAI (18.24 to 23.58 m2/g), and ESI (24.90 to 62.63 min). However, there was a decrease in pH, the value of color L*, and turbidity. The SDS-PAGE patterns showed differences in molecular weight distribution due to variations in pretreatment. All gelatin samples exhibited α1 and α2 chains as the predominant components. Interestingly, the ultrasound effect highlighted the β-chain more boldly compared to other pretreatments. FTIR spectroscopy analysis shows changes in molecular interactions due to acetic acid pretreatment followed by ultrasound, which results in shifts in the Amide A, Amide B, Amide I, Amide II, and Amide III groups. Ultrasonic treatment caused more dense and disturbed structures in the sample. Therefore, the combination of acetic acid and ultrasound pretreatment yielded the superior properties of goat skin gelatin.

In vitro antifungal activity and in vivo edible coating efficacy of insect-derived chitosan against Botrytis cinerea in strawberry

Strawberry is a perishable fruit, susceptible to development of rot by a range of fungi, in particular Botrytis cinerea. Chitosan represents an alternative to agrochemicals for improving shelf-life and fighting fungal pathogens. A chitosan-based coating derived from pupal exuviae of Hermetia illucens has been recently formulated for improving shelf-life of strawberry stored at 4 °C and mixed condition (4 °C and room temperature). The effects of a decolored (PEDEC) and not decolored (PEND) chitosan from the black soldier fly were evaluated and compared with commercial chitosans from crustaceans (CCs), in vitro and in vivo. An inhibition/reduction of fungal growth and a disturbance of normal fungal morphology were observed, being MIC of 0.5 mg mL−1 and 1 mg mL−1 and growth inhibition of 70 % and 4% for PEND and PEDEC, respectively. Both edible coatings distributed via aerograph showed equal or better potential application than CCs in controlling B. cinerea in strawberry post-harvest treated. Different effects for chitosans depended on their different molecular weight and deacetylation degree distributions, and the presence or absence of melanin pigments in their structure. PEND could act directly against the fungus, with effects predominantly associated with fungitoxic properties; PEDEC might principally provide viable alternatives, such as the elicitation of biochemical defense responses in fruits, for example through total phenols, in particular the flavonoids.

Preliminary Study on Polymerization between Hemoglobin and Enzymes during the Preparation of PolyHb-SOD-CAT-CA.

The objective of this study was to explore the influence of different factors on the aggregation effect on hemoglobin (Hb) and enzymes during the preparation of Polyhemoglobin-Superoxide dismutase-Catalase-Carbonic anhydrase (PolyHb-SOD-CAT-CA). Several factors including temperatures, pH values, Glutaraldehyde (GDA) amounts and enzymes amounts were investigated systematically to study their effects on the enzymes recoveries and polymerization rates including the Superoxide dismutase (SOD), Catalase (CAT) and Carbonic anhydrase (CA), as well as their effects on the molecular weight distribution of PolyHb-SOD-CAT-CA. Then the oxygen affinity and methemoglobin (MetHb) contents of obtained PolyHb-SOD-CAT-CA were measured to evaluate the effects of enzyme crosslinking on the properties of Polyhemoglobin (PolyHb) moieties in the molecular structure of obtained PolyHb-SOD-CAT-CA conjugate. The results showed that the enzyme recoveries and polymerization rates could be decreased with the temperatures increasing and could be generally kept stable in the physiological pH conditions, but presented only slight changes among the investigated enzyme amounts ranges. Although the GDA concentration increasing could promote the enzyme polymerization rates, the enzyme recoveries decreased in whole. The polymerization rate and molecular size of PolyHb-SOD-CAT-CA conjugate increased with the elevation of temperature and the concentration of GDA. Lastly, the P50 values, Hill coefficients, and MetHb contents of PolyHb-SOD-CAT-CA conjugate with different enzyme crosslinking degrees exhibited no obvious differences with each other. In conclusion, the polymerization reactions between enzymes and Hb molecules could be remarkably affected by temperatures, pH values, and GDA amounts, and the enzyme crosslinking presented no obvious effects on the Hb properties, especially about the oxygen affinity and oxidation degrees.

Characterisation, antibacterial activity, and prebiotic potential of dried Hermetia illucens L. larvae and of their fractions

Abstract In this study, black soldier fly (BSF) dried larvae were fractionated into their defatted, lipid, protein, and chitin-rich fractions. The samples were then characterised in terms of proximate composition, analysis of amino acids, analysis of the molecular weight distribution of proteins via gel electrophoresis, and fatty acids analysis of the lipid fraction. The antibacterial activity of all fractions was determined against Escherichia coli F4 and Streptococcus suis, two common swine pathogens. Finally, the prebiotic activity of the whole larvae and of their protein isolate and chitin-rich pellet was determined for Limosilactobacillus reuteri, a naturally occurring species in the gastro-intestinal tract of the pig. The results on amino acid profile showed that the protein extraction method used was not fully effective in cleaving chitin-bound proteins, as expected, as the true protein content of the chitin-rich sample was 48.5%. This was in accordance with the SDS-PAGE analysis, where the molecular weight distribution of proteins in the protein isolate sample did not show band at higher molecular weight, which were instead present in the chitin-rich sample. The analysis of fatty acid (FA) profile showed that lauric acid was the most abundant FA, in accordance with the literature. The results on microbiological analyses highlighted how all nitrogen-containing samples showed antibacterial activity against E. coli, the highest being the defatted fraction at 1% with a decrease of −0.77 log CFU/mL, while only the lipid fraction against S. suis (−0.48 log CFU/mL at 1%). All tested samples showed prebiotic activity for L. reuteri, but it was noticed that the increase in chitin concentration resulted in the decrease of the prebiotic effect. By combining the results of both antibacterial and prebiotic tests, it could be inferred that chitin might be considered as an antibacterial compound.