Molecular simulations of the effects of substitutions on the dissolution properties of amorphous cellulose acetate.

The dissolution behavior of cellulose acetate (CA) is an extremely important property in its extensive applications and preparation of derivatives. In this paper, we proposed a molecular model building strategy to construct amorphous CA with various substituent distributions (different degrees of substitution and substitution positions). A protocol combing molecular dynamics simulation and density functional theory (DFT) was applied to systematically investigate the dissolution behavior of CAs, and the structural properties of CAs. The reduced cohesive energy and polarity of CAs caused by the increase in substituents would enhance its solubility. The interaction of solvent molecules and CAs and the diffusion of solvent molecules in CAs have a synergistic effect on the dissolution of CAs. The diffusion coefficient is the primary factor affecting the solubility. Moreover, substituents at different positions of the anhydroglucose units along the CAs chains would produce different steric hindrance effects, which in turn affect the dissolution behavior.

Thermomechanically processed chitosan:gelatin films being transparent, mechanically robust and less hygroscopic.

Chitosan and gelatin are attractive polymeric feedstocks for developing environmentally benign, bio-safe, and functional materials. However, cost-effective methods to achieve advantageous materials properties and tailor their functionality are still lacking, but interesting. Herein, we found that physically mixing chitosan and gelatin at 1:1 (w/w) ratio resulted in materials with properties (higher Young's modulus (603.8 MPa) and tensile strength (33.6 MPa), and reduced water uptake (45%) after 6 h of water soaking) better than those of the materials based on mainly chitosan or gelatin. We attribute this synergy to the ionic and hydrogen-bonding interactions between the two biopolymers enabled by high-viscosity thermomechanical processing. Despite the lowest hygroscopicity, the 1:1 chitosan:gelatin films displayed the highest surface hydrophilicity. Besides, addition of gelatin to chitosan led to films being brighter, more transparent and amorphous. Thus, this work has generated new understanding to enhance the application of biopolymers for e.g. packaging, coating, and biomedical applications.

Effect of annealing and heat-moisture pretreatments on the oil absorption of normal maize starch during frying.

The impacts of two hydrothermal pretreatments, annealing (ANN) and heat moisture treatment (HMT), on oil-absorption by normal maize starch (NMS) during frying were investigated using low-field nuclear magnetic resonance (LF-NMR). The structural organizations of the fried samples were also evaluated using SEM, XRD, ATR-FTIR, and DSC, respectively. Both hydrothermal pretreatments significantly reduced the total oil content in the starch after frying, with the magnitude of the effect depending on the treatment conditions used. SEM showed that the pretreated fried starch granules preserved more of their original morphology. XRD, FTIR, and DSC showed that both pretreatments preserved more of the short-range double helices and long-range organizations within the orthorhombic crystalline structure for NMS during frying. The promoting effect of ANN/HMT on the interactions of starch molecules and the rearrangement of double helices were hypothesized to be responsible for the increased thermal stability of starch granules in the present work. As a result, fried starch pretreated by ANN/HMT were more organized and more compact than fried NMS, thus inhibiting oil absorption during frying.

Analysis of porous structure of potato starch granules by low-field NMR cryoporometry and AFM.

Pore size distribution is a crucial structural element affecting the adsorption and diffusion of reagents and enzymes within starch granules. An accurate and credible method of determining the pore size distribution of starch granules especially for smooth ones is therefore required. In this work, low-field NMR cryoporometry (LF-NMRC) was applied to analyze the pore structure of potato starch (PS). The reliability of the LF-NMRC method is verified by comparing with the traditional method, i.e. the low temperature nitrogen adsorption (LT-NA). Both LF-NMRC and LT-NA could characterize the PS pore structure in mesoporous range. However, LF-NMRC has superiority over LT-NA in terms of the distinguishment and determination of pore size distribution approaching to the micropores, gives more accurate and reliable results than LT-NA does. Structural evidences from scanning electron microscope (SEM) and atomic force microscope (AFM) further indicated that the new proposed method is a non-destructive method that does not induce structural changes during sample preparation.

Properties and kinetics of the in vitro release of anthocyanin-rich microcapsules produced through spray and freeze-drying complex coacervated double emulsions.

This study aimed to prepare anthocyanin-rich microcapsules by spray and freeze-drying complex coacervated double emulsion using gelatin-acacia gum (GE-AG) and chitosan-carboxymethylcellulose (CS-CMC) and to investigate their properties and in vitro release kinetics. Microencapsulation efficiency (MEE) of the microcapsules varied from 84.9% to 94.7%. CS-CMS microcapsules showed significantly higher MEEs than those of GE-AG microcapsules. A significant higher MEE and lower moisture content and hygroscopicity was observed in spray-dried double emulsion (SDE) microcapsules. Freeze-dried double emulsion (FDE) microcapsules possessed higher total anthocyanin and total phenolic contents. The best fit for release kinetics was achieved using first-order and Higuchi models for SDE and FDE microcapsules, respectively. Diffusion-controlled release in the simulated gastric fluid was found for SDE microcapsules, while erosion-controlled release in simulated gastric and intestinal fluids predominated for FDE microcapsules. These findings suggest that the microcapsules can be applied for loading anthocyanins as a nutraceutical with controllable release requirement.

Nitroso-hemoglobin-ginger conjugates effects on bacterial growth and color stability in a minced beef model.

This study aims to enhance the color and microbiological qualities of a raw beef using natural ingredients. Nitroso-hemoglobin (NO-Hb) integrated with vitamin C (VC), calcium lactate, and ginger complexation were used as natural inhibitors against the growth of aerobic and pathogenic bacteria, namely (Escherichia coli (E. coli), Staphylococcus aureus (S. aureus), and Salmonella. NO-Hb inhibited E. coli, S. aureus, and Salmonella, and enhanced the color stability more than nitrite in the minced beef model. After the multiexponential analysis of relaxation decays, the water component (T2b) was analyzed using the low-field NMR. The results indicated that, at the 7th d of cold-storage the third component (T2) was detected. Significant correlations were observed between T21 and T22 relaxation times and water-holding capacity in minced beef, implying that the LF-NMR measurements could be an efficient method for the determination and prediction of beef freshness. NO-Hb- ginger mixture, as a novel ingredient, could be used instead of nitrite in terms of meat safety.

Combining cobalt ferrite and graphite with cellulose nanocrystals for magnetically active and electrically conducting mesoporous nanohybrids.

Free-standing mesoporous membranes based on cellulose nanocrystals (CNCs) are fabricated upon the incorporation of cobalt ferrite (CoFe2O4) and graphite nanoparticles at concentrations up to 20 wt % through a soft-templating process. Scanning electron microscopy (SEM) and N2 adsorption-desorption isotherms reveal the development of highly-porous interconnected random 3D structure with surface areas up to 193.9 m2 g-1. Thermogravimetric analysis (TGA) shows an enhanced thermal stability thanks to the formation of a tortuous network limiting the hindrance of degradation by-products. Vibrating sample magnetometer (VSM) reveals a maximum magnetization saturation of 8.77 emu·g-1 with materials having either ferromagnetic or diamagnetic behaviour upon the incorporation of CoFe2O4 and graphite, respectively. Four-point-probe measurements display a maximum electrical conductivity of 9.26 ±â€¯0.04 S·m-1 when graphite is incorporated into CNCs. A proof of concept for the applicability of synthesized nanohybrids for environmental remediation is provided, presenting the advantage of their easy recovery using external magnetic fields.

Water-based 2D printing of magnetically active cellulose derivative nanocomposites.

The fabrication of magnetic materials typically involves expensive, non-scalable, time-consuming or toxic processes. Here we report a scalable, quick and environmentally-benign fabrication of magnetically active materials through screen printing using mechanically flexible paper having micron-sized pores as substrates. In comparison with traditional multicomponent inks, simple aqueous dispersions comprising solely water-soluble cellulose derivatives and cobalt ferrite nanoparticles are used. Depending on the cellulosic matrix used, inks with viscosities in the 500-2.500 mPa s range were obtained for shear rates of 20-100 s-1. Patterns with line widths from 183 to 642 µm with a maximum deviation of 9 % were fabricated. The largest magnetization saturation obtained of 0.024 emu (or 0.021 emu cm-2) for the hydroxypropyl cellulose-based ink demonstrates enough magnetization for applications in areas such as actuators and sensors. This work provides novel insights towards the processing of renewable, magnetically active and mechanically flexible materials with tailored geometries which use water as the sole solvent.

Effect of pullulan on oil absorption and structural organization of native maize starch during frying.

The oil-absorption behavior of native maize starch (NMS) during frying was investigated in the presence or absence of pullulan (PUL) using a LF-NMR method. The morphology, long-range order, short-range order, and thermal properties of fried NMS-PUL mixtures were further evaluated using SEM, XRD, ATR-FTIR, and DSC, respectively. Pullulan addition significantly reduced the oil content of the fried starch samples: 0.395, 0.310, 0.274, and 0.257 g/g in NMS with addition of 0, 1, 3, and 5% PUL, respectively (p < 0.05). SEM analysis showed that the intact granular morphology of the starch granules was preserved upon addition of pullulan. The XRD, FTIR, and DSC results showed that pullulan protected both the short-range double helices and long-range crystalline structure of the granules during frying. As a result, fried NMS-PUL mixtures were denser than fried NMS, thus inhibiting oil absorption during frying. These results may have important implications for creating healthier reduced-fat fried food products.

Photo-stability of lutein in surfactant-free lutein-zein composite colloidal particles.

The ability of nanoparticles from the plant protein zein to protect lutein from light degradation was studied under various conditions. Lutein-zein nanoparticles were synthesized, after zein purification, by anti-solvent precipitation. Particle sizes, ranging from 25 to 75 nm, measured by dynamic light scattering, were tuned by varying zein concentrations in the solvent phase (before anti-solvent precipitation), which was linked to the encapsulation efficiency. However, changes in particle sizes did not result in significant changes in photo-stability. Zein-lutein nanoparticles showed increased photo-stability of lutein when compared to lutein dispersions in water. To further promote the lutein stability, ascorbic acid was used as an antioxidant in the aqueous dispersion. The addition of ascorbic acid to lutein-zein particles resulted in dispersions with similar properties. However, the photo-stability of lutein in dispersions stabilized with ascorbic acid improved significantly compared to samples without ascorbic acid or to pure lutein dispersions (about 25% increased relative stability).

Effects of ripening stage on physicochemical properties, drying kinetics, pectin polysaccharides contents and nanostructure of apricots.

Effects of ripeness (four stages from the lowest to highest degree-I, II, III, and IV) on the physicochemical properties, pectin contents and nanostructure, and drying kinetics of apricots were investigated. The color values (L*, a*, and b*) and total soluble solid content increased during ripening, while the titratable acidity content and hardness decreased. The water-soluble pectin content increased as ripening progressed, but the chelate- and sodium carbonate-soluble pectin contents gradually declined. Atomic force microscopy imaging indicated that the pectin depolymerization occurred during ripening. Fruits at stage III obtained the highest drying rate, and the drying time was reduced by 27.27%, 17.24%, and 7.69% compared to those of stage I, II and IV, respectively. Results showed that the ripeness had significant influence on the drying kinetics, which is related to the modification of physicochemical and pectic properties. The ripeness classification is an essential operation for achieving effective drying process.

Characterization of CuO-bacterial cellulose nanohybrids fabricated by in-situ and ex-situ impregnation methods.

The aim of this research was to fabricate CuO-bacterial cellulose (BC) nanohybrids by two in-situ synthesis methods including sonochemical and precipitation methods. The ex-situ synthesized nanohybrid was also prepared by immersing BC pellicles in commercial CuO dispersion. FT-IR analysis confirmed the formation of real nanohybrid by occurring new interactions between CuO-NPs and BC. XRD results approved no disruption effect of nanohybrid formation on the crystallinity index of BC nanofibers. FE-SEM results indicated the formation of small sized NPs attached to the inner space of BC network at in-situ synthesized nanohybrids. But agglomerated NPs precipitated on the surface of BC layer was observed for ex-situ synthesized sample. In spite of higher loading capacity of ex-situ method, the in-situ synthesized nanohybrids exhibited lower release rate of NPs into the water. The antibacterial activity of ex-situ synthesized nanohybrid against S.aureus and E.coli bacteria was more than both of in-situ synthesized samples.

How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel.

Corn starches with different amylose/amylopectin ratios were used to explore the effect of rheological behaviors of concentrated system on the graft copolymerization of acrylamide and resultant hydrogels, which sheds a light on their reactive extrusion process. The viscoelastic moduli of starch melts increased with increasing amylose content (AC), leading to a decreased extent of micro-mixing detected by a reduced rheokinetic rate. With increasing AC, the graft efficiency was decreased but with almost similar monomer conversion (about 87.5%) and nearly equivalent graft content. XRD and SAXS spectra revealed that the extent of retrogradation of the starches were increased and two-phase separation was enhanced for hydrogels with increasing AC. Interestingly, microscopic analysis showed the superabsorbent hydrogel from the starch with AC of 50% exhibited a gridding membrane porous structure, resulting in a higher water absorbent capacity of 550 g/g. This was attributed to the moderate crosslinking and the slightly greater graft content.

Effect of dietary fibers on the structure and digestibility of fried potato starch: A comparison of pullulan and pectin.

The granular morphology, long-range and short-range ordered structures of fried potato starch were measured in the absence and presence of the dietary fibers. The in vitro digestibility of the fried starchy samples was also quantified using the Englyst method with logarithm-of-slope (LOS) analysis. After frying, the starch granules disintegrated, their internal crystalline structure disappeared, and the quantity of double helices present decreased. As a result of these changes, the fried starch was digested rapidly. Addition of pullulan or pectin to the samples prior to frying, reduced the structural changes observed in the starch granules during frying. Consequently, the fractions of slowly digestible and resistant starch (SDS and RS) increased significantly in the presence of the dietary fibers. These effects were attributed to the ability of the dietary fibers to sequester some of the water, thereby reducing starch granule structural changes, as well as due to their ability to coat the starch granules and interfere with the starch digestion process.

Multi-scale structure and pasting/digestion features of yam bean tuber starches.

This work discloses the multi-scale structure and pasting/digestion behaviors of yam bean tuber starches (YB-GD and YB-SC). Compared to potato starch, YB starches exhibited varied pasting/digestion features that were understood from a multi-scale structural view. Especially, YB starches showed relatively polydisperse lamellae, less perfect crystallites, and fewer amylose molecules. These features should reduce the bulk density of starch chain packing, and could facilitate the water or enzyme diffusion in starch matrixes. Consistently, not only was starch's resistance to hydrothermal effects weakened (shown by reduced pasting temperature), but also the enzyme absorption to starch chains and the subsequent hydrolysis events were accelerated. Furthermore, YB starch molecules had more short chains, which played roles in reducing the paste viscosity along with the reduced granule size and in enhancing the paste stabilities during heating and cooling. Also, those molecular features tended to speed up the enzyme diffusion and digestion events.

Impact of amylose content on structural changes and oil absorption of fried maize starches.

The absorption of oil during frying has important implications for food quality, cost, and nutrition. Maize starches with low (WMS), intermediate (NMS), and high amylose (HAMS) contents were therefore heated in oil to mimic the frying process, and the impact of amylose content on the hierarchical structures and oil absorption of the fried starches was evaluated. Amylose affected the oil absorption by interfering with the structural evolution of the starch or by directly interacting with the lipids during frying. At low moisture level (20%), the granular state was preserved after frying and so the size and porosity of the granules played a dominant role in the oil absorption process, explaining why the highest oil absorption occurred in WMS. At 40% moisture content, NMS absorbed the most oil because of its granular morphology and lower crystallinity. At 60% moisture content, HAMS absorbed more oil than NMS, because more amylose molecules in HAMS provided more hydrophobic helical cavities available for lipids.

Starch-zinc complex and its reinforcement effect on starch-based materials.

In this work, we found that ZnCl2 solution can not only be used as a plasticizer for starch but also provide a mechanical reinforcement effect to the resultant starch-based materials. By a one-step compression molding process, well-plasticized starch-based films could be obtained at 120 °C with a 15 wt.% ZnCl2 solution. Both the tensile strength and elongation at break of the films increased with a rise in ZnCl2 concentration, which demonstrates a mechanical reinforcement. This reinforcement could be mainly ascribed to the in-situ formed starch-zinc complexes and the enhanced starch molecular interactions. Moreover, if the processing method was changed into firstly mixing followed by compression molding, the tensile strength increased by more than three folds at no cost of the elongation at break. Regarding this, we propose that shear could further enhance the molecular interactions within the material. However, if the ZnCl2 concentration was too high, the mechanical properties were then reduced irrespective of the processing protocol, which could be due to the weakened molecular interactions by ZnCl2. Thus, we have demonstrated a new, simple method for preparing starch-based composite materials with enhanced mechanical properties, which could be potentially applied to many fields such as packaging, coating and biomedical materials.

Model development for non-destructive determination of rind biochemical properties of 'Marsh' grapefruit using visible to near-infrared spectroscopy and chemometrics.

Rind biochemical properties play major roles in defence mechanisms against the incidence of rind physiological disorders of citrus fruit during cold storage. Hence, multivariate calibration models were developed to rapidly and non-destructively determine rind biochemical properties of citrus fruit from visible to near-infrared (Vis/NIR) spectra acquired by Vis/NIR spectroscopy using partial least square regression algorithm. To achieve optimum models for determination of each rind biochemical property, several mathematical pre-processing methods were explored, including no pre-treatment. However, special emphases were given to the best model statistics in terms of coefficient of determination (R2) and residual predictive deviation (RPD). Models were performed by critical examination of different wavelength ranges (visible, near-infrared and full regions) and combinations of fruit harvested from different production regions and acquired before (week 0) and after (week 9) cold storage. Results obtained showed excellent models for determining parameters such as sucrose (R2 = 0.99 and RPD = 11.42), total flavonoids (R2 = 0.99 and RPD = 12.37), and chlorophyll b (R2 = 0.97 and RPD = 5.67). This study reported the first application of Vis/NIR and chemometrics in determining the rind biochemical properties of 'Marsh' grapefruit rapidly and non-destructively.

Molecular structure and properties of κ-carrageenan-gelatin gels.

Rheological studies, FTIR spectroscopy and a molecular docking approach were used to explore the structural basis of the peculiar physicochemical properties of gelatin gels modified with a κ-carrageenan admixture. Mixed gel properties are affected by the polysaccharide-to-gelatin ratio, Z, and can be divided into two categories. At low ratios, the strength of mixed gels varies insignificantly compared to gelatin due to the similar structures of the gels. Above the threshold content of κ-carrageenan (Z > 0.1), the storage modulus and yield stress of mixed gels are significantly enhanced. The nonadditivity and threshold character of the rheological properties could be the result of conformational ordering of both gelatin and κ-carrageenan, leading to the formation of additional junction zones in the gel network. According to molecular docking studies, the junctions could be formed as a result of complementary interactions between the gelatin triple helix and the κ-carrageenan double helix. The stack formation increases the interaction energy, which explains the strengthening of the gel network.

Rheokinetics of graft copolymerization of acrylamide in concentrated starch and rheological behaviors and microstructures of reaction products.

A widely recognized challenge in starch chemistry is to manipulate the graft copolymerization onto starch melt by reactive extrusion (REX). To understand the complex in-situ graft copolymerization in highly concentrated systems, we firstly used a mixer to achieve a homogeneous viscous starch melt, and then undertook dynamic rheological measurements to study the rheokinetics of the reaction. The in-situ synthesis also facilitated the characterization of the microstructures of reaction products. The melt mixture could be regarded to be completely micromixed since the rheokinetics was predominated by the reaction kinetics. The rheological characterization revealed that G'of hydrogels followed a linear progression with the crosslinker concentration. Nevertheless, the reaction temperature and initiator content had little influence on the final microstructure of hydrogels, most likely due to the strong chain transfer reaction in the melt. Additionally, high-amylose starches tended to form grafted hydrogels with a high physical crosslinking density.