Three types of fish bones including fish skull, rib, and backbone were cooked at 120 °C for 20 min to remove tissues and impurities. The fish bones were minced and ground into microscaled particles before treated in a high-energy wet ball mill to obtain nanoparticles. The effects of bone structure on size reduction of fish bone particles during nanomilling and the calcium release properties were investigated. The results showed that fish rib has higher elasticity modulus than fish skull and fish backbone due to its highly ordered structure. Prior to nanomilling of ground fish bones, the particle size of the skull was the greatest followed by backbone and rib. The mean particle size and calcium release were not significantly different after 8-h nanomilling. However, the size reduction and calcium release rates of the nanoparticles were similar between fish skull and backbone while the fish rib had the lowest values in both categories. The kinetics of size reduction during nanomilling and the calcium release properties of the nanoparticles were well described with the first-order exponential decay function and first-order kinetic function, respectively. Correlation analysis indicated that among all mechanical properties, elasticity modulus of fish bone, to the highest degree, determined their size reduction rate and calcium release rate during nanomilling.

•Okara insoluble dietary fiber (IDF) was downsized to nanometer range by wet milling.•Molecular and crystalline structure of IDF was disrupted after milling.•Particle size reduction of the IDF contributed to modify physicochemical properties.•Modified okara IDF may be applied as functional ingredient in foods.Changes in structural characteristics and physicochemical properties of okara insoluble dietary fiber (IDF) during high-energy wet media milling process were analyzed. Particle size of the IDF was effectively reduced from 66.7 μm to 544.3 nm after 6 h of milling and kept constant (p > 0.05) as the milling process prolonged. As the particle size decreased, lightness and whiteness of the IDF significantly (p < 0.05) increased, zeta potential decreased continuously (p < 0.05). Swelling power, water solubility index and apparent viscosity extensively increased (p < 0.05) after 1 h of milling and then steadily decreased (p < 0.05). Electron microscopy observations showed that the IDF was changed from regular and compact rods to aggregates with puffed morphology. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis revealed that intermolecular hydrogen bonds and crystalline structure of the IDF polysaccharides were disturbed after milling.Download high-res image (205KB)Download full-size image

Biofortification of staple grains with high contents of essential micronutrients is an important strategy to overcome micronutrient malnutrition. However, few attempts have targeted at γ-aminobutyric acid (GABA), a functional nutrient for aging populations. In this study, two rice cultivars, Heinuo and Xianhui 207, were used to investigate changes in GABA and other nutritional compounds of dehulled rice after germination under normoxic and hypoxic conditions. Forty-one metabolites were identified in both cultivars treated by normoxic germination, whereas the germinated dehulled rice of Heinuo and Xianhui 207 under hypoxic treatment had 43 and 41 metabolites identified, respectively. GABA increased in dehulled rice after germination, especially under hypoxia. Meanwhile, a number of other health-beneficial and/or flavor-related compounds such as lysine and d-mannose increased after the hypoxic treatment. The accumulation of GABA exhibited genotype-specific modes in both normoxic and hypoxic treatments. With regard to GABA production, Xianhui 207 was more responsive to the germination process than Heinuo, whereas Heinuo was more responsive to hypoxia than Xianhui 207. This study provides a promising approach to biofortify dehulled rice with increased GABA and other nutrients through metabolomic-based regulation.

•CaCl2 could promote unfolding of myosin during setting at 40 °C.•Myosin aggregated via hydrophobic interactions, disulfide bonds and Ca bridges.•The extent and rate aggregation of myosin increased along with CaCl2.•Good gelling properties were associated with an appropriate aggregation.The effect of CaCl2 on denaturation and aggregation of silver carp myosin incubated at 40 °C was investigated by circular dichroism spectroscopy, surface hydrophobicity (S0-ANS), total sulfhydryl (SH) group content, zeta potential, turbidity, z-average diameter (dz), and dynamic rheological analysis. During setting at 40 °C, both CaCl2 and heating induced conformational changes of the fish myosin, and exposure of more hydrophobic amino acid residues and free SH groups, followed by myosin aggregation via hydrophobic interactions and disulfide bonds. Additionally, turbidity and dz of myosin increased significantly with increasing CaCl2 concentration, and the added CaCl2 further increased the extent and rate of aggregation of myosin by promoting the formation of Ca bridges. Myosin with 60 mM CaCl2 showed the maximal G′ value and the highest rate of G′ development. However, the G′ value would decrease with an excessive amount of CaCl2 (100 mM).

•Denaturation rates of actomyosin and myosin depended on setting temperatures.•More network structures were formed at 40–45 °C than those at 25–30 °C.•Thermal stability of actomyosin was higher than that of myosin.•Viscoelastic gel was formed when actomyosin and myosin were denatured sufficiently.Thermal inactivation kinetics of Ca2+-ATPase, changes in turbidity and rheological properties of actomyosin and myosin from yellowcheek carp during setting at different temperatures were investigated. Actomyosin and myosin setting at 40–45 °C exhibited greater extent and more rapid Ca2+-ATPase inactivation compared to at 25–30 °C. Formation of protein aggregates and three-dimensional network structures of actomyosin and myosin at 25–30 °C was far less than those at 40–45 °C. Thermal stability of actomyosin was higher than that of myosin as revealed by its higher activation energy for the inactivation of Ca2+-ATPase. Actomyosin and myosin also exhibited different dynamic rheological properties, especially when the setting temperatures were 40 and 45 °C.

The LW03 strain was isolated from Chinese farmland soil and found to be able to secrete certain enzymes degrading regenerated cellulose films at low temperature. The LW03 strain was systematically identified as Rhizopus arrhizus var. arrhizus by morphological, physiological, and molecular methods. Incubation of regenerated cellulose films with the extracted crude enzyme of LW03 was done to measure morphological changes by using scanning electron microscopy. Microscopic observations showed that the morphology of the regenerated cellulose films changed drastically due to enzymatic hydrolysis. The extracellular hydrolases of LW03 strain incubated on bran medium were also assessed. The predominant activity in the crude enzyme was glucoamylase activity, followed by acid proteinase, phytase and pectinase activity. Interestingly, activities of β-glucosidase, endoglucanase, exoglucanase, and cellulase were also observed, but at a much lower extent. Based on initial evidence, the crude enzyme is most likely to contain some new constituents capable of degrading regenerated cellulose films.

Dynamic rheological behavior of actomyosin from yellowcheek carp (YAM) and grass carp (GAM) during gelling was investigated at different protein concentrations. The viscoelastic properties of YAM and GAM solutions and gels were also studied. Before heating, YAM and GAM solutions exhibited the weak gel-like behavior. After heating and cooling, G′ of YAM was much higher than the corresponding value of GAM. During heating and cooling, the G′ values of actomyosin showed a strong relationship with protein concentration for both yellowcheek carp and grass carp. The thermal gelation profiles of YAM and GAM solutions were remarkably different. The gelation temperature of actomyosin decreased with the increasing protein concentration. The gelation temperature of GAM exhibited stronger concentration dependence than that of YAM. Enthalpy of gelation reaction of YAM and GAM was 509.2 and 146.6 kJ/mol, respectively.

Effects of CaCl2 on chemical interactions, textural properties and expressible moisture content of suwari and kamaboko gels from yellowcheek carp and grass carp were investigated. And the correlations between the contents of chemical interactions and physical properties of surimi gels were analyzed. The contents of chemical interactions, especially non-disulfide covalent bonds, disulfide bonds and hydrophobic interactions of suwari and kamaboko gels, varied with addition concentration of CaCl2 and fish species. Suwari and kamaboko gels from yellowcheek carp exhibited higher breaking force, deformation and gel strength than these from grass carp. Surimi gels (suwari and kamaboko gels) from yellowcheek carp and grass carp exhibited their maximum gel strength when 40 mmol/kg and 100 mmol/kg CaCl2 was added, respectively. Addition of CaCl2 at high concentration resulted in low water holding capacity of surimi gels. Correlation analysis indicated that the contents of nonspecific associations, ionic bonds, hydrophobic interactions and sulfhydryl groups exhibited significant correlation with breaking force of surimi gels from yellowcheek carp and grass carp. Additionally, the content of non-disulfide covalent bonds had significant positive correlations with breaking force and expressible moisture of surimi gel from yellowcheek carp.

The morphology and physicochemical properties of mechanically activated rice starch (MARS) isolated from three rice cultivars were investigated by scanning electron microscopy, X-ray diffractometry, gel permeation chromatography and Rapid Visco Analysis. The shape of rice starch granule changed from native polyhedron to anomalistic state during mechanical activation. It was suggested that the hydration of starch and moisture was an important factor for granules agglomeration which appeared more easily with higher moisture content. Mechanical force resulted in destroying of starch crystal structure which disappeared basically after activated for 10 h. As the mechanical activation time prolonged, the amylopectin and amylose of rice starch were both decomposed gradually, thus causing the increase of cold-water solubility and reducing power and the decrease of BV. Meanwhile, the pasting temperature and the viscosity of MARS decreased, including peak viscosity, final viscosity, breakdown viscosity and setback viscosity. The crystalline and molecular structure of rice starch with 6.02% moisture content were more easily destroyed by mechanical force than those with 1.05% and 11.05% moisture content, which resulted in higher cold-water solubility and reducing power, lower BV, pasting temperature, peak viscosity, final viscosity, breakdown viscosity and setback viscosity.

The relationships between gel properties and the secondary structures of silver carp myosin were investigated at pH 5.5–9.0 using dynamic rheological measurement, circular dichroism and scanning electron microscopy. The gel properties of fish myosin were strongly pH and temperature dependent. During heating at 1 °C/min, myosin formed gels in the pH range 5.5–7.5, but not at pH 8.0–9.0. α-Helix was the predominant structure at pH 7.0. The α-helix fraction declined with increasing temperature and the pH away from 7.0, whilst the other secondary structure fractions increased. The α-helix structure of myosin was more susceptive to acid-treatment than alkali-treatment. As pH increased, the gelation rate and gel strength decreased, and the water-holding capacity (WHC) showed an increasing trend followed by a plateau. High β-sheet and β-turn fractions prior to heating could improve G′ at 90 °C, but they depressed the WHC. A compact and uniform gel of fish myosin was obtained at pH 7.0.

Rheological properties of actomyosin (AM) solutions from silver carp and pork were investigated by means of rotational rheometer, and described by the power law model. AM solution behaved as pseudoplastic fluid under all test conditions (AM concentration: 4–25 mg/mL; temperature: 5–45 °C; ionic strength: 0–1.0 M; pH: 6.7–12.3). Systems with higher protein concentration exhibited bigger consistency coefficients and smaller flow indexes than those with lower protein concentration. Compared with pork AM solution, consistency coefficient of fish AM solution was higher at corresponding protein concentration, and its increase with respect to AM concentration was more prominent. Consistency coefficient declined with increasing temperature and pH. The Arrhenius model described successfully the temperature dependence of consistency coefficient (p < 0.001). Activation energy of fish AM solution was lower than that of pork AM solution. With increasing ionic strength, consistency coefficient of fish AM solution showed an increasing trend while that of pork AM increased and then decreased.

Effects of temperature, pH and ionic strength on the stability of actomyosin (AM) from fish and pork were studied using UV spectra, solubility, turbidity, and sulfhydryl group content measurement for comparison. Pork AM exhibited higher stability to cold storage and heating than fish AM. The unfolding rate of AM increased with increasing temperature. Intense aggregation occurred over 30 °C for fish AM and 40 °C for pork AM. New disulfide bonds mainly formed over 40 °C for fish AM and 60 °C for pork AM. Pork AM exhibited the higher turbidity than fish AM in the range of 50–90 °C, suggesting the higher extent of aggregation of pork AM. Ionic strength mainly influenced solubility of AM, but there was no effect on cleavage and formation of disulfide bond. The lowest solubility of both AM was at pH 5.42. Additionally, fish AM was more sensitive to pH changes than pork AM.

•Nano-scaled fish bone (about 110 nm) was prepared using wet ball milling.•Thermal temperature affected breakage and calcium release of fish bone.•As temperature increased, bone became porous and mechanical parameters decreased.•120 °C & 20 min was optimal for breakage and calcium release of fish bone.Effects of thermal treatments on breakage and calcium release of fish bone particles during high-energy wet ball milling were investigated. Heating temperature (55–130 °C) showed much more obvious influences on the breakage and calcium release than heating time (20–60 min). As heating temperature increased from 55 °C to 120 °C, fish bone matrix became more porous, and mechanical parameters of fish bone remarkably decreased (p < 0.05). Furthermore, particle size of the fish bone after milling reached a limit (approximate 110 nm) in a shorter time and calcium release was enhanced. Regardless of heating time, size of the fish bone particles was not significantly different (p > 0.05) between the samples treated with 120 °C and 130 °C during milling, while calcium release was higher for the latter sample. Breakage kinetics and calcium release of fish bone particles were fitted with the first-order exponential decay function and the Higuchi equation, respectively.