Production and characterization of recrystallized linear α-glucans at different temperatures for controllable thermostability and digestibility.

Molecular structure of linear α-glucans (LAGs) and crystallization temperature have great effects on the thermostability and digestibility of recrystallized LAGs, but the recrystallization behaviors of LAGs in response to temperature remain unclear. Here LAGs with different lengths were prepared from amylopectin via chain elongation and debranching. Recrystallization of LAGs at 4 °C yielded B-type crystalline structure with relative crystallinity ranged from 23.7% to 46.1%. With a chain length of 40.2, an A-type allomorph was observed for a slow recrystallization at 50 °C. Differential scanning calorimetry suggested that A-type crystal had a higher thermostability than the B-type crystal, and increasing LAGs' chain length improved the dimension of double helices, whose assembly produced starch crystallites that enhanced the thermostability and decreased the in vitro digestibility of recrystallized LAGs. An improved thermostability of recrystallized LAGs preserved their ordered structures and kept the resistance to digestive enzymes, with a RS content up to 75.4%.

Molecular modulating of amylopectin's structure promoted the formation of starch-unsaturated fatty acids complexes with controlled digestibility and improved stability to oxidation.

In this study, waxy corn starch (WCS) was modified by amylosucrase and pullulanase, producing linear starch chains with elongated length that favored the complexation with unsaturated fatty acids (uFAs). Compared to native WCS, the amylosucrase-modified WCS with an average chain length of 47.8 was easier to form V-type complexes with oleic acid, while increasing the degree of unsaturation impeded the formation of V-type complexes. The pullulanase treatment hydrolyzed the branching points of amylosucrase-modified WCS and the linear starch chains could forme V-type complexes with oleic acid, linoleic acid, and linolenic acid, with V-type crystallinity decreasing from 38.2 % to 20.1 %. V-type complexes had a lower thermal stability than the B-type starch crystallites, and their peak melting temperature ranged from 67.2 to 79.0 °C. The content of resistant starch in the complexes was in the range of 21.8 %-40.9 % and the formation of V-type complexes decreased the susceptibility of uFAs to oxygen.

Specific ions effect on aggregation behaviors and structural changes of amyloid fibrils from rice glutelin.

Metal ions have been considered as an important factor on fibrils assembly. Herein, a comprehensive analysis of specific ions effect on fibril formation and structural changes was investigated. The addition of ions (except Zn2+) accelerated the aggregation kinetics of rice glutelin fibrils (RGFs) from 0.93 to 1.28-2.19 h-1. In addition, the fibrillization rate followed the order of NH4+ > Li+ > Na+ > K+ > Cu2+ > Mg2+ > Ca2+ > Zn2+. The highest yield and length of fibrils were observed with Ca2+, probably due to the ionic bridging effect and hydrated capacity of Ca2+. However, Cu2+ reduced the fibrils yield, which was attributable to the fact that Cu2+ disrupted ß-sheet structure and inhibited the transition of monomer to fibrils. The polymorphism of fibrils was observed with different salts, and the light metals presented a superior effect on fibrils formation than heavy metals. Overall, this work will provide a further information into how to tune the structure of RGFs using various ions.

Salting-out effect-mediated size-control of protein nanoparticles towards controllable microstructures for sustained release of eugenol.

Size and monodispersity of solid particles are essential to their structuring behaviors at biphasic interfaces. However, delicate control over biomolecular nanoparticle sizes is challenging. In this study, we prepared monodisperse rice protein (RP) nanoparticles by neutralizing RP solutions (pH 12.0) using combined treatments of cationic exchange resins (CERs) and HCl. CERs absorbed Na+ by releasing H+ without producing salt during neutralization. By compromising the usages of CERs and HCl when preparing RPs, the generation of NaCl can be delicately tailored, leading to controllable nanoparticle sizes from 20 nm to 30 nm. By mixing these nanoparticles with eugenol in an aqueous solution, the nanoparticles accommodated eugenol in their cores due to inward diffusion. Furthermore, such eugenol-contained nanoparticles with different sizes demonstrated tunable releases of eugenol due to size-dependent capillary forces, which can be harnessed for suppression of microbial growth on fruit with prolonged effective eugenol concentration.

Monodisperse Plant Protein Nanoparticles Prepared by Cation-Exchange Resins for Stabilization of Pickering Emulsions.

Our understanding of the microstructure of many plant proteins is based on the ancient and conventional methods of alkali extraction and acid precipitation, which generate considerable amounts of NaCl causing salting-out effects and aggregation of their molecules. In this study, monodisperse rice protein (RP) nanoparticles were prepared using cation-exchange resins that release H+ and absorb Na+, thus avoiding the generation of NaCl during neutralization of the alkali extracts. The generated RP nanoparticles of small diameter (20 nm) and excellent uniformity (0.17 polydispersity) quickly diffuse to and stabilize the oil-water interface, producing oil-in-water Pickering emulsions. The emulsifying ability and emulsion stability afforded with these nanoparticles were 17 and 3.5 times higher than those of nanoparticles prepared by conventional alkali extraction and acid precipitation methods, respectively. Furthermore, increased RP nanoparticle concentration created more stable emulsions with smaller droplets and reduced flocculation index vital for practical applications. This study provides a convincing example of how to prepare monodisperse protein nanoparticles that adsorb at a fluid interface, which may find numerous applications in food and cosmetic formulations.

Impact of crystalline structure on the digestibility of amylopectin-based starch-lipid complexes.

In this study, chain-elongated waxy corn starch (mWCS) was complexed with lauric acid (LA) to produce starch-lipid complexes (mWCS@LA) with a mixture of B- and V-type crystalline structures. Results from in vitro digestion showed that mWCS@LA had higher digestibility than mWCS, and the logarithm of slope plots of mWCS@LA revealed a two-stage digestion pattern, with digestion rate of the first stage (k1 = 0.038 min-1) being much higher than that of the following stage (k2 = 0.0116 min-1). The complexation between the long branch chains of mWCS and LA formed amylopectin-based V-type crystallites that were rapidly hydrolyzed during the first stage. The digesta isolated from the second stage of digestion had a B-type crystallinity of 52.6 %, and starch chains with degree of polymerization of 24-28 mainly contributed to the formation of the B-type crystalline structure. The results from the present study reveal that the B-type crystallites were more resistant to amylolytic hydrolysis than the amylopectin-based V-type crystallites.

Biomolecular 1D Necklace-like Nanostructures Tailoring 2D Janus Interfaces for Controllable 3D Enteric Biomaterials.

Construction of well-ordered two-dimensional (2D) and three-dimensional (3D) assemblies using one-dimensional (1D) units is a hallmark of many biointerfaces such as skin. Mimicking the art of difunctional properties of biointerfaces, which skin exhibits as defense and shelter materials, has inspired the development of smart and responsive biomimetic interfaces. However, programming the long-range ordering of 1D base materials toward vigorous control over 2D and 3D hierarchical structures and material properties remains a daunting challenge. In this study, we put forward construction of 3D enteric biomaterials with a two-strata 2D Janus interface assembled from self-adaptation of 1D protein-polysaccharide nanostructures at an oil-water interface. The biomaterials feature a protein dermis accommodating oil droplets as a reservoir for bioactive compounds and a polysaccharide epidermis protecting them from gastric degradation. Furthermore, the epidermis can be fine-tuned with different thicknesses rendering enteric delivery of a bioactive cargo (coumarin-6) with controllable retention in the intestinal tract from 6 to 24 h. The results highlight a skin-inspired construction of enteric biomaterials by self-adaptation of 1D nanostructures at the oil-water interface toward 2D Janus biointerfaces and 3D microdevices, which can be tailored for intestinal treatments with intentional therapeutic efficacies.

Tuning the electrostatic interaction between rice protein and carboxymethyl cellulose toward hydrophilic composites with enhanced functional properties.

Protein-polysaccharide interactions have attracted much attention due to inherent potential in generating new structures and functionalities. In the present study, by simply mixing rice proteins (RPs) with carboxymethyl cellulose (CMC) at pH 12.0 prior neutralization, novel protein-polysaccharide complexes (RCs) were structured with water dispersibility and functionalities highly dependent on the degree of substitution (DS) and molecular weight (Mw) of CMC. Specifically, the water-dispersibility of RPs was increased from 1.7 % to 93.5 % at a RPs/CMC mass ratio of 10:1 with CMC of DS1.2 (Mw = 250 kDa). Fluorescence and circular dichroism spectra showed suppressed folding tendency of RPs by CMC during neutralizing the basicity, indicating controllable protein conformations. Furthermore, the structures of RCs became more unfolded for CMC with a larger DS or a smaller Mw. This enabled RCs with highly controllable functionalities in terms of emulsifying and foaming properties, which may have promising applications in developing food matrix with customized structures and textures.

Resistant starch formation mechanism of amylosucrase-modified starches with crystalline structure enhanced by hydrothermal treatment.

The aim of this study was to reveal the underlying mechanism contributing towards the formation of resistant starch (RS) in amylosucrase-modified starches with crystalline structure enhanced by hydrothermal treatment. The branch chains of waxy corn starch were continuously elongated by amylosucrase, and the retrogradation of elongated starches with weight-average chain length (CLw¯) of 27.0-37.6 yielded B-type retrograded starches (MSs) with crystallinity increasing from 33.1 % (MS-5) to 41.4 % (MS-30). Increasing the starch crystallinity improved the content of RS from 6.7 % of MS-5 to be as much as 41.0 % of MS-30. During the hydrothermal treatment, MS-5 with CLw¯ of 27.0 favored the B â†’ A allomorphic transition, leading to the decreased starch digestibility. Moreover, the hydrothermal treatment facilitated the assembly of double helices to increase starch crystallinity, which further increased the content of RS. The findings of the present study may assist the preparation of functional starches with controllable digestibility.

Impacts of Proanthocyanidin Binding on Conformational and Functional Properties of Decolorized Highland Barley Protein.

The impacts of interaction between proanthocyanidin (PC) and decolorized highland barley protein (DHBP) at pH 7 and 9 on the functional and conformational changes in DHBP were investigated. It was shown that PC strongly quenched the intrinsic fluorescence of DHBP primarily through static quenching. PC and DHBP were mainly bound by hydrophobic interactions. Additionally, free sulfhydryl groups and surface hydrophobicity obviously decreased in DHBP after combining with PC. The zeta potential of DHBP-PC complexes at pH 7 increased significantly. A change in the structure of DHBP was caused by interactions with PC, resulting in an increase in the number of ß-sheets, a decrease in the number of α-helixes, and a spectral shift in the amide Ⅱ band. Furthermore, the presence of PC enhanced the foaming properties and antioxidant activity of DHBP. Overall, this study suggests that DHBP-PC complexes at pH 7 could be designed as a stable additive, and illustrates the potential applications of DHBP-PC complexes in the food industry.

Fixing zein at the fibrillar carboxymethyl cellulose toward an amphiphilic nano-network.

In this study, co-assembled protein-polysaccharide complexes (ZCs) were prepared by fixing zein nanoparticles at the fibrillar carboxymethyl cellulose (CMC) by pH-driven anti-solvent precipitation. The complexation boosted the dispersity of zein from 17.3% to 88.6%. Scanning electron microscopy and atomic force microscopy confirmed the formation of network structures where the fibrous polysaccharides inserted into the interval of granular proteins. Circular dichroism spectrum, fluorescence spectrum, and X-ray diffraction verified the electrostatic interaction pattern between zein and CMC. Besides, the ZCs presented favorable amphiphilic properties, and the electrostatic interaction between zein and CMC can be fine-tuned by the substitution degree (DS) of carboxymethyl in CMC. Therefore, the Pickering emulsions stabilized by ZCs had controllable size and long-term stability using DS as a stimulus. Our study offers a novel strategy developing bio-based materials as novel stabilizers of Pickering emulsions.

Modifying functional properties of food amyloid-based nanostructures from rice glutelin.

Amyloid-based nanostructures from food sources have been received intensive interests recently in material science, biomedicine and especially delivery system. This is due to the ability of protein-based amyloid architecture that proved to be an attractive system to carry drug and nutrition. However, few research focused on the modification of functional properties of different fractions isolated from amyloid fibrils. Hereby, we separated the retentate (RGFs) and filtrate (FGFs) fractions from rice glutelin fibrils (GFs) using centrifugal filtration and then investigated the structural characteristics and functional properties of these fractions. We proved that protein fibrillization would highly improve both emulsifying and antioxidant abilities of protein dispersion. In addition, further processed RGFs with rich ß-sheet structures exhibited a similar functional performance to GFs dispersion. By contrast, FGFs dispersion with less ß- sheet content, lower molecular weight, interestingly re-assembled into spherical aggregates with weaker interaction, exhibiting better antioxidant and emulsifying properties.

Fabrication and characterization of starch-lipid complexes using chain-elongated waxy corn starches as substrates.

In this study, waxy corn starch (WCS) was enzymatically modified by amylosucrase, followed by complexation with lauric acid (LA) to produce starch-lipid complexes. Compared to the native WCS with average chain length (CL¯) of 25.4, the amylosucrease-modified WCSs showed a significantly higher CL¯ ranging from 29.3 to 52.5. The complexation with lauric acid inhibited the reassociation of starch chains, producing V-type complexes with crystallinity reached as much as 42.4 %. Besides, the melting of V-type complexes presented endothermic peaks at Tp of 55.1-60.4 °C, and thermal stability of V-type complexes had a negative correlation with the V-type crystallinity. In vitro digestion implies that the formation of V-type complexes gradually increased the content of rapidly digestible starch and accordingly decreased the content of resistant starch. This study may provide an efficient technology to produce V-type starch-lipid complexes with controllable physical and digestion properties using waxy starch as substrate.

Hydrothermal induced B → A allomorphic transition in retrograded starches with side chains elongated by amylosucrase to different lengths.

In this study, chain-elongated starches were modified with hydrothermal treatment to produce hydrothermal-treated starches with different crystalline structures. All chain-elongated starches showed a B-type crystalline structure and the retrogradation of long branch chains accelerated the formation of starch crystallites. The hydrothermal treatment preserved the granular structure of starches but facilitated the rearrangement of starch chains to generate crystallites. Starches with short chain length favored the B â†’ A allomorphic transition during the hydrothermal treatment. A longer chain length of starch led to greater stability of double helices and accordingly inhibited the B â†’ A allomorphic transition, resulting from the hydrogen bonding along with the direction of helix restrained the displacement of the helix. The longer double helices resulted in higher gelatinization temperature of the chain-elongated starches. Moreover, the gelatinization temperature of the starches was further enhanced by the hydrothermal treatment, and both increased crystallinity and B â†’ A allomorphic transition contributed to the improved thermal stability of the hydrothermal-treated starches.

Effects of decolorization on aggregation behavior of highland barley proteins: Comparison with wheat proteins.

To explore effects of decoloration on highland barley proteins (HBPs) aggregation, physicochemicalproperties, structuralcharacteristics, and functional characteristics of decolorized highland barley proteins (DHBPs) were investigated. In order to compare the aggregation of HBPs, wheat proteins (WPs) were selected as a control group. The solubility, turbidity, particle size and surfacehydrophobicity of HBPs increased obviously (P < 0.05) after decoloration, but still lower than WPs. Electrophoretic analysis showed that the bands amount of HBPs and DHBPs were lower than WPs, while decolorization had no effect on the bands amount of HBPs. Moreover, chemical bonds contents of DHBPs were higher than HBPs, but significant lower (P < 0.05) than WPs. The Fourier-transform infrared spectroscope showed that secondary structures of HBPs were more flexible after decoloration. Besides, foaming property, emulsifying property and water holding capacity of DHBPs increased significantly (P < 0.05). To conclude, the aggregation behavior and functional properties of HBPs were improved by the decolorization.

Complete genome sequence of Roseivivax marinus strain TCYB24 with quorum sensing system reveal the adaptive mechanism against deep-sea hydrothermal environment.

Roseivivax marinus strain TCYB24 is a rod-shaped bacterium of Rhodobacteraceae isolated from the gill of deep-sea mussel Bathymodiolus marisindicus which collected from the Tiancheng hydrothermal vent under depth of 2700 m on the southwest Indian ridge. In our previous study, the strain TCYB24 was proved to produce quorum sensing signal of N-Acyl-homoserine lactones (AHLs) and form biofilm. In order to determine its adaptive mechanism against the extreme environment of deep-sea hydrothermal vents, the whole genome was sequenced by high-throughput Illumina tag sequencing. The results show the whole genome consists of one circular chromosome and eight circular plasmids, with a total length of 4.60 Mb (G + C content of 67.4%), 4338 open reading frames, 46 tRNAs and 6 rRNA operons. According to the genome-wide functional annotation, numbers of heavy metal resistance, high pressure and cold adapting related genes were found. In addition, genes about exopolysaccharide (EPS) biosynthesis and secretion and biofilm formation, which facilitate bacteria to resist extreme environments, were identified. Intriguingly, a pair of RaiI/R-type quorum sensing system was discovered firstly in the bacterium isolated from hydrothermal environment. The results may help to understand genetic underpinning of extreme environmental adaptation mechanism of bacteria in deep-sea hydrothermal area.

Removal of aflatoxin B1 from aqueous solution using amino-grafted magnetic mesoporous silica prepared from rice husk.

It is urgent to solve the contamination of aflatoxin B1 (AFB1) in food and water. In this study, the mesoporous silica was prepared from rice husk, which was then magnetized using the precipitation technique, followed by amino-modification with 3-aminopropyltriethoxysilane, forming amino-grafted magnetic mesoporous silica (NMMS). X-ray diffraction, Fourier transformed infrared spectra, and thermogravimetric analysis showed the successful grafting of amino groups on NMMS with a percentage of grafting up to 13.33%. The NMMS had an adsorption capacity of 169.88 µg/g and a removal rate of 93.43% for AFB1 in aqueous solutions at 20 °C, pH 7.0 for 2.0 h. The adsorption of AFB1 by NMMS followed a quasi-second-order kinetics and fitted well with the Langmuir model. Furthermore, the removal rate of AFB1 by NMMS remained 72.43% after repeating the adsorption-desorption process for five times. This study provided a facile approach to prepare NMMS for effective removal of AFB1.

All-natural protein-polysaccharide conjugates with bead-on-a-string nanostructures as stabilizers of high internal phase emulsions for 3D printing.

The combination of proteins and polysaccharides creates an exceptional platform for stabilizing biphasic systems such as oil in water emulsions. In this paper, we propose the use of natural protein-polysaccharide conjugates (PPCs) extracted from shiitake mushroom roots to stabilize high internal phase emulsions (HIPEs). The PPCs had bead-on-a-string nanostructures with bead (300 nm in diameter) and string (50 nm in thickness) structures corresponding to proteins and polysaccharides, respectively. Having spaced compartments with favourable amphiphilic properties, the PPCs had a three-phase contact angle close to 90°, which were harnessed for the preparation of HIPEs with excellent long-term storage stability (30 d) and heat tolerance (90 °C). The HIPEs were amenable to three-dimensional printing, yielding different objects with strong self-standing and high structural resolution properties. This paper presents a good example of how these unique PPC structures can provide biphasic stabilization, HIPE preparation, and potential applications in food products.

Entrapping curcumin in the hydrophobic reservoir of rice proteins toward stable antioxidant nanoparticles.

Loading hydrophobic phytochemicals by protein particles is challenged by either insufficient loading capacity or colloidal instability. In this study, hydrosoluble curcumin-loaded nanoparticles were prepared using hydrophobic rice proteins (RPs). The fabrication was facilitated by dissolving curcumin and RPs at pH 12.0 before neutralizing the basicity. The formation of nanoparticles was studied by fluorescence and infrared spectroscopy, and the microstructures were studied by transmission electron microscopy. The results showed the entrapping of curcumin inside the hydrophobic reservoir formed by the acid-induced refolding of RPs. Due to promoted burial of the hydrophobic moieties, the curcumin-loaded RP-nanoparticles displayed excellent colloidal stability during the 28-day storage. Bearing 144.41 mg/g protein of curcumin, the nanoparticles demonstrated prominent antioxidant properties, with the DPPH scavenging capacity increased by up to 88.62% compared to the free curcumin. This study harnessed hydrophobic attractions as a tool for management of the protein-phytochemical interactions, overcoming colloidal instabilities of both individual components.

Synthesis of Rice Husk-Based MCM-41 for Removal of Aflatoxin B1 from Peanut Oil.

Edible oils, especially peanut oil, usually contain aflatoxin B1 (AFB1) at extremely high concentrations. This study focused on the synthesis of rice husk-based mesoporous silica (MCM-41) for the removal of AFB1 from peanut oil. MCM-41 was characterized by X-ray diffraction, N2 physisorption, and transmission electron microscope. MCM-41 was shown to have ordered channels with high specific surface area (1246 m2/g), pore volume (1.75 cm3/g), and pore diameter (3.11 nm). Under the optimal concentration of 1.0 mg/mL of the adsorbent dose, the adsorption behavior of MCM-41, natural montmorillonite (MONT), and commercial activated carbon (CA) for AFB1 were compared. The adsorption of AFB1 in peanut oil onto the three adsorbents was slower compared to that of AFB1 in an aqueous solution. In addition, the pseudo-second-order kinetic model better fit the adsorption kinetics of AFB1, while the adsorption mechanism followed the Langmuir adsorption isotherm on the three adsorbents. The calculated maximum adsorbed amounts of AFB1 on MONT, MCM-41, and CA were 199.41, 215.93, and 248.93 ng/mg, respectively. These results suggested that MCM-41 without modification could meet market demand and could be considered a good candidate for the removal of AFB1 from peanut oil. This study provides insights that could prove to be of economic and practical value.