Yanping Cao

Physicochemical stability, microrheological properties and microstructure of lutein emulsions stabilized by multilayer membranes consisting of whey protein isolate, flaxseed gum and chitosan.

The impact of chitosan (CTS) on the physicochemical stability, microrheological property and microstructure of whey protein isolate (WPI)-flaxseed gum (FG) stabilized lutein emulsions at pH 3.0 was studied. A layer-by-layer electrostatic deposition method was used to prepare multilayered lutein emulsions. Droplet size, zeta-potential, instability index, microstructure and microrheological behavior of lutein emulsions were measured. The influences of interfacial layer, metal chelator and free radical scavenger on the chemical stability of lutein emulsions were also investigated. It was found that multilayer emulsions had better physical stability showing the pronounced effect of 1wt% CTS. The mean square displacement analysis demonstrated that CTS led to increases of macroscopic viscosity and elasticity index for WPI-FG stabilized lutein emulsions due to CTS embedding in the network. CTS also helped to chemically stabilize the lutein emulsions against degradation. The combination of interfacial membrane and prooxidative metal chelator or free radical scavenger was an effective method to control lutein degradation.

Inhibitory effect of wheat bran feruloyl oligosaccharides on oxidative DNA damage in human lymphocytes.

The present work assessed the protective effect of feruloyl oligosaccharides (FOs), the ferulic acid ester of oligosaccharides from wheat bran, against oxidative DNA damage in normal human peripheral blood lymphocytes induced by hydrogen peroxide (H2O2). The DNA damage was measured by using the single cell gel electrophoresis assay (comet assay). Lymphocytes were subjected to DNA damage by exposure to a range of H2O2 concentrations (10-200μmol/l). H2O2, at a concentration of 200μmol/l, resulted in nearly all cells being highly damaged. FOs showed no cytotoxicity and genotoxicity to normal human lymphocytes at the tested concentrations (10-500μmol/l). In addition, DNA damage in human lymphocytes induced by 100μmol/l H2O2 was inhibited by FOs in a concentration-dependent fashion with 91.1% inhibition of lymphocyte DNA damage at 500μmol/l as compared with the control. The results suggest that water-soluble FOs from wheat bran are able to enhance the ability of human lymphocytes to resist H2O2 induced oxidative damage.

Molecular weight distribution, rheological property and structural changes of sodium alginate induced by ultrasound.

In this study, the effects of ultrasound with different ultrasonic frequencies on the properties of sodium alginate (ALG) were investigated, which were characterized by the means of the multi-angle laser light scattering photometer analysis (GPC-MALLS), rheological analysis, circular dichroism (CD) spectrometer and scanning electron microscope (SEM). It showed that the molecular weight (Mw) and molecular number (Mn) of the untreated ALG was 1.927×105g/mol and 4.852×104g/mol, respectively. The Mw of the ultrasound treated ALG was gradually increased from 3.50×104g/mol to 7.34×104g/mol while the Mn of ALG was increased and then decreased with the increase of the ultrasonic frequency. The maximum value of Mn was 9.988×104g/mol when the ALG was treated by ultrasound at 40kHz. It indicated that ultrasound could induce ALG degradation and rearrangement. The number of the large molecules and small molecules of ALG was changed by ultrasound. The value of dn/dc suggested that the ultrasound could enhance the stability of ALG. Furthermore, it was found that ALG treated by ultrasound at 50kHz tended to be closer to a Newtonian behavior, while the untreated and treated ALG solutions exhibited pseudoplastic behaviours. Moreover, CD spectra demonstrated that ultrasound could be used to improve the strength of the gel by changing the ratio of M/G, which showed that the minimum ratio of M/G of ALG treated at 135kHz was 1.34. The gel-forming capacity of ALG was correlated with the content of G-blocks. It suggested that ALG treated by ultrasound at 135kHz was stiffer in the process of forming gels. The morphology results indicated that ultrasound treatment of ALG at 135kHz increased its hydrophobic interaction and interfacial activity. This study is important to explore the effect of ultrasound on ALG in improving the physical properties of ALG as food additives, enzyme and drug carriers.

Influence of sodium alginate pretreated by ultrasound on papain properties: Activity, structure, conformation and molecular weight and distribution.

The aim of the study was to investigate the impact of sodium alginate (ALG) pretreated by ultrasound on the enzyme activity, structure, conformation and molecular weight and distribution of papain. ALG solutions were pretreated with ultrasound at varying power (0.05, 0.15, 0.25, 0.35, 0.45W/cm(2)), 135kHz, 50°C for 20min. The maximum relative activity of papain increased by 10.53% when mixed with ALG pretreated by ultrasound at 0.25W/cm(2), compared with the untreated ALG. The influence of ultrasound pretreated ALG on the conformation and secondary structure of papain were assessed by fluorescence spectroscopy and circular dichroism spectroscopy. The fluorescence spectra revealed that ultrasound pretreated ALG increased the number of tryptophan on papain surface, especially at 0.25W/cm(2). It indicated that ultrasound pretreatment induced molecular unfolding, causing the exposure of more hydrophobic groups and regions from inside to the outside of the papain molecules. Furthermore, ultrasound pretreated ALG resulted in minor changes in the secondary structure of the papain. The content of α-helix was slightly increased after ultrasound pretreatment and no significant change was observed at different ultrasound powers. ALG pretreated by ultrasound enhanced the stability of the secondary structure of papain, especially at 0.25W/cm(2). The free sulfhydryl (SH) content of papain was slightly increased and then decreased with the increase of ultrasonic power. The maximum content of free SH was observed at 0.25W/cm(2), under which the content of the free SH increased by 6.36% compared with the untreated ALG. Dynamic light scattering showed that the effect of ultrasound treatment was mainly the homogenization of the ALG particles in the mixed dispersion. The gel permeation chromatography coupled with the multi-angle laser light scattering photometer analysis showed that the molecular weight (Mw) of papain/ALG was decreased and then increased with the ultrasonic pretreatment. Results demonstrated that the activity of immobilized papain improved by ultrasonic pretreatment was mainly caused by the variation of the conformation of papain and the effect of interactions between papain and ALG. This study is important to explain the intermolecular interactions of biopolymers and the mechanism of enzyme immobilization treated by ultrasound in improving the enzymatic activity. As expected, ALG pretreated by appropriate ultrasound is promising as a bioactive compound carrier in the field of immobilized enzyme.

Effect of ultrasound on the diffusion properties of casein entrapped in alginate–chitosan gel

The effects of ultrasound-assisted and pre-ultrasound treatment on the diffusion properties of casein imbedded by alginate-chitosan gel were investigated. The fluorescence spectrophotometry for determining the fluorescence intensity of casein was established to calculate the diffusion coefficient (De). Scanning electron microscope (SEM) was used to observe the microstructure of gel beads. The results showed that two different kinds of ultrasonic treatments had obvious distinctions on the casein diffusion. As the frequency increased, the value of De decreased from 28.56 × 10(-4)m(2)s(-1) (28 kHz) to 2.57 × 10(-4)m(2)s(-1) (135 kHz) during the ultrasound-assisted process. While, the minimum De of 8.6 × 10(-4)m(2)s(-1) was achieved at the frequency of 50 kHz for the pre-ultrasound treatment. The impact of power on the diffusion showed that De increased with the increase of ultrasound power until it reached the highest value 28.56 × 10(-4)m(2)s(-1) (0.45 W/cm(2)) in the ultrasound-assisted process. It would reach the maximum value (16 × 10(-4)m(2)s(-1)) when the power was 0.25 W/cm(2) in the pretreatment ultrasound process. SEM analysis exhibited that the gel structural changes (area ratio) were in accordance with De through different ultrasonic treatment. This was mainly due to the mechanical action and cavitation of the ultrasonic treatment. This study is important to explain the diffusion properties of large molecules and explore the mechanism of enzyme immobilization treated by ultrasound.

Low-frequency and low-intensity ultrasound accelerates alliinase-catalysed synthesis of allicin in freshly crushed garlic.

BACKGROUND The well-known chemically and therapeutically active compound allicin is formed in crushed garlic by the interaction of alliin with alliinase. In this study, low-frequency and low-intensity ultrasound was employed to accelerate the alliinase-catalysed synthesis of allicin in freshly crushed garlic. RESULTS The optimal conditions for improvement of the alliinase-catalysed synthesis of allicin in freshly crushed garlic were found to be as follows: ultrasound intensity 0.4 W cm⁻², ultrasound frequency 50 kHz, enzymatic reaction temperature 35 °C and reaction time 30 min. Under these conditions the yield of allicin was increased by about 25.2% compared with the control without ultrasound. Alliinase in the freshly crushed garlic was purified by ammonium sulfate precipitation and gel filtration on a Sephacryl S-200 column. The employed ultrasound increased the activity of the purified alliinase by about 42.8%, did not affect the enzymes temperature optimum and improved its thermal stability. CONCLUSION The results of this study indicated that the activity of alliinase in freshly crushed garlic might be enhanced by low-frequency and low-intensity ultrasound, thereby accelerating the alliinase-catalysed conversion of alliin in garlic to allicin.

Enhancing physicochemical properties of emulsions by heteroaggregation of oppositely charged lactoferrin coated lutein droplets and whey protein isolate coated DHA droplets

The formation and physicochemical stability of mixed functional components (lutein & DHA) emulsions through heteroaggregation were studied. It was formed by controlled heteroaggregation of oppositely charged lutein and DHA droplets coated by cationic lactoferrin (LF) and anionic whey protein isolate (WPI), respectively. Heteroaggregation was induced by mixing the oppositely charged LF-lutein and WPI-DHA emulsions together at pH 6.0. Droplet size, zeta-potential, transmission-physical stability, microrheological behavior and microstructure of the heteroaggregates formed were measured as a function of LF-lutein to WPI-DHA droplet ratio. Lutein degradation and DHA oxidation by measurement of lipid hydroperoxides and thiobarbituric acid reactive substances were determined. Upon mixing the two types of bioactive compounds droplets together, it was found that the largest aggregates and highest physical stability occurred at a droplet ratio of 40% LF-lutein droplets to 60% WPI-DHA droplets. Heteroaggregates formation altered the microrheological properties of the mixed emulsions mainly by the special network structure of the droplets. When LF-coated lutein droplets ratios were more than 30% and less than 60%, the mixed emulsions exhibited distinct decreases in the Mean Square Displacement, which indicated that their limited scope of Brownian motion and stable structure. Mixed emulsions with LF-lutein/WPI-DHA droplets ratio of 4:6 exhibited Macroscopic Viscosity Index with 13 times and Elasticity Index with 3 times of magnitudes higher than the individual emulsions from which they were prepared. Compared with the WPI-DHA emulsion or LF-lutein emulsion, the oxidative stability of the heteroaggregate of LF-lutein/WPI-DHA emulsions was improved. Heteroaggregates formed by oppositely charged bioactive compounds droplets may be useful for creating specific food structures that lead to desirable physicochemical properties, such as microrheological property, physical and chemical stabilities.

Impact of Ultrasound on the Physical Properties and Interaction of Chitosan–Sodium Alginate

The aim of the study was to investigate the impact of ultrasound on the physical properties and interaction of chitosan (CHI)-sodium alginate (ALG) by rheological behavior, dynamic light scattering, and isothermal titration calorimetry (ITC). The CHI–ALG solutions were treated with ultrasound at 50°C, 0.45 W/cm2 and different frequencies (28 and 40 kHz) for different times (10 and 30 minutes). Ultrasonic treatment effectively decreased the viscosity and consistency coefficient and increased the flow behavior index of the CHI–ALG solution, leading to its change in the flow behavior from pseudoplastic to near-Newtonian behavior. It was interesting to find that ultrasonic treatment slightly decreased G′ and increased G″, which indicated that ultrasound strengthened the fluid character and weakened the solid nature of CHI–ALG. The particle size distribution of ultrasonic treated CHI–ALG solutions was shifted to lower values compared to the untreated sample. ITC analysis showed that there was an increase in the affinity constant. However, thermodynamic parameters enthalpy (ΔH), entropy (ΔS), and Gibbs free energy change (ΔG) were not obviously affected by ultrasonication. These results suggested that ultrasonic treatment of CHI–ALG would affect the molecular diffusion by changing the wall material nature and further impact the immobilized enzyme activity. GRAPHICAL ABSTRACT

Effects of nonionic surfactants on pigment excretion and cell morphology in extractive fermentation of Monascus sp. NJ1: Nonionic surfactants and Monascus extractive fermentation

BACKGROUND Different nonionic surfactants in submerged fermentation of Monascus sp. demonstrate significant differences regarding increasing pigment yield. In this study, 15 surfactants from five series were analyzed to investigate the influence of nonionic surfactants on Monascus pigments, with the aim of simultaneously obtaining a novel nonionic surfactant. RESULTS Addition of the novel surfactant Brij 35 greatly enhanced pigment excretion and demonstrated good biocompatibility. Extracellular red, orange and yellow pigments increased by 1.47-, 1.71- and 2.07-fold respectively. Production of extracellular pigments was not only related to the hydrophile-lipophile balance value (HLB) but also affected by the cloud point temperature (CP) of the fermentation medium. It was found that nonionic surfactants can improve cell membrane permeability and cell storage capacity by modifying the cell walls of Monascus mycelium and by increasing lipid droplet levels, enhancing pigment excretion. Different nonionic surfactants modify Monascus mycelium to different degrees. CONCLUSION The novel surfactant Brij 35, which has good capacity for pigment extraction and biocompatibility, was identified in the analysis. The effects of nonionic surfactants on the secretion of pigments are related to not only the modification of the cell wall and internal structure but also the CP and HLB.

Modification of physicochemical properties by heteroaggregation of oppositely charged lactoferrin and soybean protein isolate coated DHA emulsion droplets

In this study, the effect of heteroaggregation (HA) on the physicochemical stability and the formation of volatile substances of DHA emulsions was investigated. HA-DHA emulsions were produced by combination of lactoferrin (LF)-DHA and soy protein isolate (SPI)-DHA emulsions at pH 6.0. Zeta-potentials, droplet sizes, stability, and microstructures were measured as a function of different ratios of LF-DHA to SPI-DHA droplets. DHA oxidation of single and HA emulsions was determined through measurements of lipid hydroperoxides, thiobarbituric acid reactive substances, and the formation of volatile substances. LF-DHA to SPI-DHA droplets ratios of 5:5, 4:6, and 3:7 formed stable emulsions. The lowest zeta-potential, biggest droplet size, and optimum physical stability of heteroaggregated emulsion occurred at a 5:5 of LF-DHA to SPI-DHA droplet ratio. Microstructure behavior indicated that the HA emulsions (LF-DHA droplets/SPI-DHA droplets = 5:5) formed specific three-dimensional uniform networks. The formation of thiobarbituric acid reactive substances, lipid hydroperoxides, and volatile compounds including hexanal and ( E, E)-2,4-heptadienal decreased in HA compared to single emulsions. The results indicated that the physicochemical stability of DHA emulsions was enhanced and that the formation of volatile substances was inhibited by HA. It thus demonstrated the utilization of HA to improve the stability of bioactive compounds in emulsions.