Correlation of the hierarchical structure with rheological behavior of polypseudorotaxane gel composed of pluronic and ß-cyclodextrin.

We have identified the hierarchical (primary, secondary, tertiary and quaternary) structures of a polypseudorotaxane (PPR) gel composed of the Pluronic F108 and ß-cyclodextrin system to be ß-cyclodextrin crystalline, lamellar sheets, lamellar stacks and "grains", respectively. The correlation between the rheological properties and the proposed structures under shear flows was rationalized. Alignment of lamellar stacks and reorganization of grain boundaries under shear flows were investigated by rheo-SANS, small angle X-ray scattering and small-angle light scattering. The relaxation of highly aligned lamellar stacks is slow (>2 h) after flow cessation compared to that of the regrouped grains (a few minutes). The main contribution to thixotropic behavior is likely from the faster relaxation of the reorganized grains containing highly oriented lamellar stacks. The comprehensive understanding of structure-function relationship of the PPR gel will facilitate the rational design for its applications.

What causes the anomalous aggregation in pluronic aqueous solutions?

Pluronic (PL) block copolymers have been widely used as delivery carriers, molecular templates for porous media, and process additives for affecting rheological behavior. Unlike most surfactant systems, where unimer transforms into micelle with increased surfactant concentration, anomalous large PL aggregates below the critical micelle concentration (CMC) were found throughout four types of PL (F108, F127, F88 and P84). We characterized their structures using dynamic light scattering and small-angle X-ray/neutron scattering. Molecular dynamics simulations suggest that the PPO segments, though weakly hydrophobic interaction (insufficient to form micelles), promote the formation of large aggregates. Addition of acid or base (e.g. citric acid, acetic acid, HCl and NaOH) in F108 solution significantly suppresses the aggregate formation for up to 20 days due to the repulsion force from the attached H3O+ molecules on the EO segment in both PEO and PL and the reduction of CMC through the salting out effect, respectively.

Fine structures of self-assembled beta-cyclodextrin/Pluronic in dilute and dense systems: a small angle X-ray scattering study.

The evolution of the fine structures of self-assembled polypseudorotaxane (PPR) in Pluronic (PL F108) solutions containing dilute to dense beta-cyclodextrin (ß-CD) was illustrated for the first time by small angle X-ray scattering (SAXS). Dense ß-CD (∼19 w/v%) was found feasible to be dispersed in 24% citric acid solution. 5% of PL F108 formed cylindrical micelles of 1 nm in radius and 8 nm in length in the presence of 24% citric acid through the dehydration of citric acid and citrate. PPR was formed through host-guest interaction between PL F108 and ß-CD. In dilute ß-CD system (1%), the single chains of PPR with separated ß-CD stacks on PL F108 were formed. The numbers of ß-CD in each stack increased from 1 to 4 on increasing ß-CD concentration to 9%. In a dense ß-CD system, PPR condensed to correlated structures majorly composed of two unit blocks through the hydrogen bonds between PPRs. Two distinguishable correlated domains with correlation lengths of 50 nm (marked α-phase) and 46 nm (marked ß-phase) along the chains, but without fine periodic structure within each individual domain, were identified in the 10% ß-CD solution. Periodic stacking of ß-CD in the domains developed in the 12% solution. As ß-CD concentration increased from 12 to 19%, the correlated heights of α and ß phases reduced from 41 and 32 nm to 30 and 10 nm, respectively. There were 48 ß-CDs that stabilized on each PL F108 chain in the 19% ß-CD system, which is in good agreement with stoichiometry.

Expression of a gene encoding ß-ureidopropionase is critical for pollen germination in tomatoes.

Global warming has seriously decreased world crop yield. High temperatures affect development, growth and, particularly, reproductive tissues in plants. A gene encoding ß-ureidopropionase (SlUPB1, EC 3.5.1.6) was isolated from the stamens of a heat-tolerant tomato (CL5915) using suppression subtractive hybridization. SlUPB1 catalyzes the production of ß-alanine, the only ß-form amino acid in nature. In the anthesis stage, SlUPB1 expression in CL5915 stamens, growing at 35/30°C (day/night), was 2.16 and 2.93 times greater than that in a heat-sensitive tomato (L4783) cultivated at 30/25°C or 25/20°C, respectively. Transgenic tomatoes, upregulating SlUPB1 in L4783 and downregulating SlUPB1 in CL5915, were constructed, and the amount of ß-alanine measured by liquid chromatography-electrospray ionization-mass spectrometry in the transgenic overexpression of SlUPB1 was higher than that of L4783. However, the ß-alanine in the transgenics downregulating SlUPB1 was significantly lower than the ß-alanine of CL5915. Pollen germination rates of these transgenics were analyzed under different developmental and germinating temperatures. The results indicated that germination rates of transgenics overexpressing SlUPB1 were higher than germination rates of the background tomato L4783. Germination rates of transgenics downregulating SlUPB1 were significantly lower than germination rates of background tomato CL5915, indicating the necessity of functional SlUPB1 for pollen germination. Pollen germinating in the buffer with the addition of ß-alanine further indicated that ß-alanine effectively enhanced pollen germination in tomatoes with low SlUPB1 expression. Together, these results showed that the expression of SlUPB1 is important for pollen germination, and ß-alanine may play a role in pollen germination under both optimal and high temperatures.

The effect of reduction on the properties of the regioselectively oxidized starch granules prepared by bromide-free oxidation system.

Development of intact oxidized starch granules by regioselective oxidation technology is of interest and provides a new research direction for oxidized starch. In this study, new sodium tetrahydridoborate (NaBH4)-treated oxidized starch (OS-BH4) granules were prepared by a one-pot method, where native corn starch (NS) granules were oxidized by 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)/sodium hypochlorite (NaClO) system followed by reduction with NaBH4. Oxidized starch (OS) granules without NaBH4 reduction were also prepared to investigate the effect of C6 aldehyde groups remained after TEMPO-mediated oxidation on properties of the granules. When degrees of oxidation were controlled to be not higher than 12%, both the OS and OS-BH4 granules had similar morphology to the NS granules with envelopes. Compared to the OS granules, except for lower pasting temperatures and dextrose equivalents, the OS-BH4 granules had higher molecular weights, degrees of polymerization (DP), peak viscosities, final viscosities, and swelling power. Difference of the properties was considered related to (1) repulsive forces formed between the C6 carboxylate groups, (2) C6 aldehyde groups with lower hydrophilicity than the C6 hydroxyl groups, and (3) some hemiacetal linkages formed between the C6 aldehyde groups and the hydroxyl groups. Furthermore, pregelatinized OS-BH4 granules were preliminarily prepared, which showed good swelling behavior with intact granular morphology in alkaline environment.

Gut microbiota-directed intervention with high-amylose maize ameliorates metabolic dysfunction in diet-induced obese mice.

Obesity is a chronic disease that may lead to the development of metabolic diseases, cardiovascular diseases, and cancers and has been predicted to affect one billion adults by 2030. Owing to the pivotal role of the gut microbiota in health, including metabolism and energy homeostasis, dietary fiber, the primary energy resource for the gut microbiota, not only helps reduce appetite and short-term food intake but also modulates the structure of the gut microbiota. In this study, we investigated whether high-amylose maize (HAM), with a particular amount of dietary fiber, improves dysmetabolism and gut microbiota dysbiosis in diet-induced obese mice. Promisingly, the HAM dietary intervention not only reduced body weight gain, adipocyte hypertrophy, and dyslipidemia but also mitigated non-alcoholic fatty liver disease, insulin resistance, impaired glucose tolerance, and inflammation in the liver and epididymal white adipose tissues in high-fat diet (HFD)-fed obese mice. In addition, the HAM dietary intervention ameliorated gut microbiota dysbiosis in HFD-fed mice. Changes in families, genera, and species of gut biota that have a relative abundance of 0.01% in at least one group were scrutinized. At the species level, HAM dietary intervention increased Bifidobacterium pseudolongum, Bifidobacterium animalis, Bifidobacterium bifidum, and Lactobacillus paraplantarum and decreased Streptococcus agalactiae, Mucispirillum schaedleri, and Alistipes indistinctus. This change in the gut microbiota driven by the HAM diet was strongly associated with obesity-related indices, highlighting the nutraceutical potential of HAM for improving overall metabolic health. Taken together, this study demonstrates the potential of the HAM diet for mediating metabolic syndrome and gut microbiota dysbiosis.

Second harmonic generation imaging - a new method for unraveling molecular information of starch.

We present a new method, second harmonic generation (SHG) imaging for the study of starch structure. SHG imaging can provide the structural organization and molecular orientation information of bio-tissues without centrosymmetry. In recent years, SHG has proven its capability in the study of crystallized bio-molecules such as collagen and myosin. Starch, the most important food source and a promising future energy candidate, has, for a decade, been shown to exhibit strong SHG response. By comparing SHG intensity from different starch species, we first identified that the SHG-active molecule is amylopectin, which accounts for the crystallinity in starch granules. With the aid of SHG polarization anisotropy, we extracted the complete χ((2)) tensor of amylopectin, which reflects the underlying molecular details. Through χ((2)) tensor analysis, three-dimensional orientation and packing symmetry of amylopectin are determined. The helical angle of the double-helix in amylopectin is also deduced from the tensor, and the value corresponds well to previous X-ray studies, further verifying amylopectin as SHG source. It is noteworthy that the nm-sized structure of amylopectin inside a starch granule can be determined by this far-field optical method with 1-µm excitation wavelength. Since SHG is a relatively new tool for plant research, a detailed understanding of SHG in starch structure will be useful for future high-resolution imaging and quantitative analyses for food/energy applications.

Novel pH-responsive granules with tunable volumes from oxidized corn starches.

Novel pH-responsive granules with tunable volume from oxidized starch granules were prepared from waxy and normal corn starches using 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-mediated oxidation and pregelatinization. Conditions of both oxidation and pregelatinization were designed on the basis of maintaining intact granules' morphology. Carboxylate groups at C6 in anhydroglucose of the oxidized starch acting as pH-responsivity controllers were introduced to by TEMPO/NaClO/NaClO2 system at pH 6.8 to achieve degrees of oxidation of 9-10%. Formation of the carboxylate groups was confirmed by Fourier transform infrared spectroscopy and thermogravimetric analysis. The TEMPO-oxidized waxy and normal corn starch granules (TWSG and TNSG) were pregelatinized at 65 °C for 5 and 16 min, respectively, to provide desirable swelling capacity of granules. The anionic pregelatinized TWSG and TNSG show swelling ratios of 15.6 and 11.7 at pH 2 and 31.6 and 25.0 at pH 7, respectively, exhibiting good pH-responsivity and potentials for active compounds delivery applications.

MicroRNA160 Modulates Plant Development and Heat Shock Protein Gene Expression to Mediate Heat Tolerance in Arabidopsis.

Global warming is causing a negative impact on plant growth and adversely impacts on crop yield. MicroRNAs (miRNAs) are critical in regulating the expression of genes involved in plant development as well as defense responses. The effects of miRNAs on heat-stressed Arabidopsis warrants further investigation. Heat stress increased the expression of miR160 and its precursors but considerably reduced that of its targets, ARF10, ARF16, and ARF17. To study the roles of miR160 during heat stress, transgenic Arabidopsis plants overexpressing miR160 precursor a (160OE) and artificial miR160 (MIM160), which mimics an inhibitor of miR160, were created. T-DNA insertion mutants of miR160 targets were also used to examine their tolerances to heat stress. Results presented that overexpressing miR160 improved seed germination and seedling survival under heat stress. The lengths of hypocotyl elongation and rachis were also longer in 160OE than the wild-type (WT) plants under heat stress. Interestingly, MIM160 plants showed worse adaption to heat. In addition, arf10, arf16, and arf17 mutants presented similar phenotypes to 160OE under heat stress to advance abilities of thermotolerance. Moreover, transcriptome and qRT-PCR analyses revealed that HSP17.6A, HSP17.6II, HSP21, and HSP70B expression levels were regulated by heat in 160OE, MIM160, arf10, arf16, and arf17 plants. Hence, miR160 altered the expression of the heat shock proteins and plant development to allow plants to survive heat stress.

Bioactive compounds in legumes and their germinated products.

Nineteen domestic legume varieties, including 6 soybeans, 7 black soybeans, 4 azuki beans, and 2 mung beans, were evaluated for contents of dietary fiber, total phenolics, and flavonoids. Nine varieties of legumes (black soybean TN6, TN3, BM, and WY; soybean KS1, KS2, and KS8; azuki bean AKS5 and AKS6) were good sources of bioactive compounds and were selected for germination tests. After short- and long-term germinations, the bioactive compounds were determined and compared with compositions of isoflavones in soybeans. The reducing power of legumes correlated well with their total flavonoid contents (r (2) = 0.9414), whereas less correlation was found between reducing power and total phenolics contents (r (2) = 0.6885). The dark-coat seeds, such as azuki beans and black soybeans, contained high amounts of phenolic compounds and contributed to high antioxidative ability, whereas their phenolics content and antioxidative abilities significantly decreased after short-term germination due to losses of pigments in the seed coats. After long-term germination, the contents of bioactive compounds (total phenolics and flavonoids) increased again and the ratio of aglycones to total isoflavones significantly increased in black soybeans. TN3 and TN6 seeds and their long-term germinated seeds and AKS5 seeds were identified as the legume samples that might have the highest antioxidant ability according to the results of chemometric analysis. Selection of the right legume varieties combined with a suitable germination process could provide good sources of bioactive compounds from legumes and their germinated products for neutraceutical applications.

Bioactive compounds and antioxidative activity of colored rice bran.

The profiles of bioactive compounds (including phenolics and flavonoids in free and bound fractions, anthocyanins, proanthocyanidins, vitamin E, and γ-oryzanol) of outer and inner rice bran from six colored rice samples collected from local markets were investigated. Proanthocyanidins could only be detected in red rice bran but not in black rice bran. The free fraction of the extracts dominated the total phenolics (72-92%) and the total flavonoids (72-96%) of colored rice bran. Most of the phenolic acids (83-97%) in colored rice bran were present in the bound form. Protocatechualdehyde was identified for the first time in the bound fraction of red rice bran by high performance liquid chromatography-photodiode array/electrospray ionization tandem mass spectrometry. The antioxidative activities of the free fraction of the colored rice bran were attributed to the proanthocyanidins in red colored rice and anthocyanins in black rice, while that of the bound fraction was mainly due to the phenolic acids.

Characteristics of the starch fine structure and pasting properties of waxy rice during storage.

Two waxy rice (TNW1 and TCSW1, exhibiting high and low amylase activity, respectively), were stored at 4 and 17 °C (polished rice) and at room temperature (paddy rice) for 15 months. The fine structure of starch isolated from the aged rice and the pasting properties of starch and rice flour were studied. After storage, the percentage of short amylopectin (AP) chains increased in TNW1, and no uniform changing pattern was observed in the chain-length (CL) distribution of TCSW1. The viscosity of starch isolated from the aged rice increased as the storage temperature and duration increased. We hypothesised that this increase was due to the hydrolysis of AP by endogenous amylase and the generation of small clusters during storage, which caused the simple dissociation of AP and a high swelling degree of starch granules during gelatinisation. Factor analysis of the first two factors associated with the characteristics of viscograms and the CL of AP explained 72% of the total variation.

Correlated changes in structure and viscosity during gelatinization and gelation of tapioca starch granules.

Melting of native tapioca starch granules in aqueous pastes upon heating is observed in situ using simultaneous small- and wide-angle X-ray scattering (SAXS/WAXS) and solution viscometry. Correlated structure and viscosity changes suggest closely associated amylose and amylopectin chains in the semicrystalline layers, and the release of amylose chains for enhanced solution viscosity occurs largely after melting of the semicrystalline structure. Before melting, WAXS results reveal mixed crystals of A- and B-types (∼4:1 by weight), whereas SAXS results indicate that the semicrystalline layers are composed of lamellar blocklets of ca 43 nm domain size, with polydisperse crystalline (≃7.5 nm) and amorphous (≃1.1 nm) layers alternatively assembled into a lamellar spacing of ≃8.6 nm with 20% polydispersity. Upon melting, the semicrystalline lamellae disintegrate into disperse and molten amylopectin nanoclusters with dissolved and partially untangled amylose chains in the aqueous matrix which leads to increased solution viscosity. During subsequent cooling, gelation starts at around 347 K; successively increased solution viscosity coincides with the development of nanocluster aggregation to a fractal dimension ≃2.3 at 303 K, signifying increasing intercluster association through collapsed amylose chains owing to decreased solvency of the aqueous medium with decreasing temperature.