Effects of high acyl gellan gum on the rheological properties, stability, and salt ion stress of sodium caseinate emulsion.

Sodium caseinate (SC) is widely used as a biological macromolecular emulsifier in oil-in-water (O/W) emulsions. However, the SC-stabilized emulsions were unstable. High-acyl gellan gum (HA) is an anionic macromolecular polysaccharide that improves emulsion stability. This study aimed to investigate the effects of HA addition on the stability and rheological properties of SC-stabilized emulsions. Study results revealed that HA concentrations >0.1 % could increase Turbiscan stability, reduce the volume average particle size, and increase the zeta-potential absolute value of the SC-stabilized emulsions. In addition, HA increased the triple-phase contact angle of SC, transformed SC-stabilized emulsions into non-Newtonian fluids, and effectively inhibited the movement of emulsion droplets. The effect of 0.125 % HA concentration was the most effective, allowing SC-stabilized emulsions to maintain good kinetic stability over a 30-d period. NaCl destabilized SC-stabilized emulsions but had no significant effect on HA-SC emulsions. In summary, HA concentration had a significant effect on the stability of SC-stabilized emulsions. HA altered the rheological properties and reduced creaming and coalescence by forming a three-dimensional network structure, increasing the electrostatic repulsion of the emulsion and the adsorption capacity of SC at the oil-water interface, and thereby improving the stability of SC-stabilized emulsions during storage and in the presence of NaCl.

Development of natamycin-loaded zein-casein composite nanoparticles by a pH-driven method and application to postharvest fungal control on peach against Monilinia fructicola.

This work fabricated natamycin-loaded zein-casein nanoparticles (N-Z/C NPs) by a pH-driven approach and applied to control postharvest peach brown rot caused by Monilinia fructicola. When casein and phosphoric acid were used as a stabilizer and neutralizing acid, respectively, NPs with mean particle sizes < 100 nm and zeta-potentials < -30 mV could be obtained. The NPs could increase the aqueous dispersibility of natamycin and showed high stability against environmental changes, which could be attributed to both hydrophobic stacking and hydrogen bonds between natamycin and zein. Besides, the effects of N-Z/C NPs on the storage of peach were assessed in vitro and in vivo. Nanoencapsulation did not affect the antifungal activities of natamycin. The NPs with 20 and 80 µg/mL of natamycin could basically inhibit the spore germination and mycelial growth of M. fructicola, respectively. The N-Z/C NPs coatings exhibited better results than natamycin in controlling of peach brown rot.

Effect of Hydrothermal Treatment on the Structure and Functional Properties of Quinoa Protein Isolate.

The aim of this study was to investigate the effects of hydrothermal treatment at different temperatures and times on the structure and functional properties of quinoa protein isolate (QPI). The structure of QPI was investigated by analyzing changes in the intrinsic fluorescence spectrum, ultra-violet (UV) spectrum, and Fourier transform infrared spectrum. The solubility, water/oil-holding capacity, emulsifying activity, and emulsion stability of QPI were studied, as were the particle size and the thermogravimetric properties of QPI. The results showed that the average particle size of QPI gradually increased with the increase in hydrothermal treatment time and temperature, and reached a maximum value of 121 °C for 30 min. The surface morphology also became rough and its thermal stability also increased. The endogenous fluorescence and UV spectral intensity at 280 nm decreased gradually with increasing hydrothermal treatment time and temperature, and reduced to the minimum values at 121 °C for 30 min, respectively. After hydrothermal treatment, the secondary structure of QPI tended to be disordered. The functional properties of QPI after treatment were all superior to those of the control. The results of this study might provide a basis for the processing and utilization of QPI.

Antibacterial Activity and Mechanism of Action of Whey Protein-ε-Polylysine Complexes against Staphylococcus aureus and Bacillus subtilis.

ε-Polylysine (ε-PL) is a cationic antimicrobial peptide, which easily forms complexes with food polyanions to weaken its antibacterial activity. A whey protein-ε-PL complex delivery system was found to be able to solve this problem. This study investigated the antimicrobial activity of the complexes and their mechanism against Gram-positive bacteria. The minimal inhibitory concentration of the complexes with different ε-PL contents against Staphylococcus aureus and Bacillus subtilis were 19.53-31.26 and 3.90-7.81 µg/mL, respectively, which were similar to free ε-PL. Furthermore, the whey protein-ε-PL complexes had a strong bactericidal effect on Bacillus subtilis. The inhibition zone diameters of the complexes against Staphylococcus aureus and Bacillus subtilis containing 5000 µg/mL of ε-PL were 14.14 and 16.69 mm, respectively. The results of scanning electron microscopy showed that the complexes could destroy the cell membrane structure in Bacillussubtilis, resulting in holes on the surface, but not in Staphylococcus aureus. The results of molecular dynamics simulation showed that under electrostatic interaction, the complexes captured the phospholipid molecules of the bacterial membrane through the hydrogen bonds. Parts of the ε-PL molecules of the complexes were embedded in the bilayer membrane, and parts of the ε-PL molecules could penetrate the bilayer membrane and enter the bacterial internal environment, forming holes on the surface of the bacteria. The antibacterial results in fresh meat showed that the whey protein-ε-PL complexes could reduce the total mesophilic and Staphylococcus aureus counts. This study on the antibacterial activity mechanism of whey protein-ε-PL complexes could provide a reference for the application of ε-PL in protein food matrices.

Fabrication of High-Acyl Gellan-Gum-Stabilized ß-Carotene Emulsion: Physicochemical Properties and In Vitro Digestion Simulation.

The ß-carotene emulsion system using high-acyl gellan gum (HA) as an emulsifier was fabricated and systematically studied. The stability and stabilizing mechanism of the emulsion using medium-chain triglyceride as oil phase with a water-oil mass ratio of 9:1 under different physicochemical conditions of heat, pH, and ions were investigated by analyzing mean particle size (MPS), emulsion yield (EY), and dynamic stability. The effects of the HA-ß-carotene emulsion system on the bioaccessibility of ß-carotene in vitro were conducted. During the simulated oral digestion stage (SODP) and simulated gastric digestion stage (SGDP), the emulsion systems stabilized with different HA contents showed good stability, and the changes of MPS and zeta potential (ZP) were within 2.5 µm and 3.0 mV, respectively. After entering the simulated intestinal digestion phase (SIDP), ß-carotene was released from oil droplets and formed micelles with bile salts, phospholipids, etc. HA-ß-carotene emulsion can enhance the release rate of free fatty acid (FFA), which ultimately affects the ß-carotene bioaccessibility. These results indicate that HA can be used to prepare carotene emulsion and improve its bioavailability. The study provides a reference for the application of HA as a natural emulsifier and the delivery of ß-carotene.

Structure, stability, rheology, and texture properties of ε-polylysine-whey protein complexes.

ε-Polylysine (ε-PL) is a natural preservative of antimicrobial peptides with broad spectrum and high antibacterial properties. The electrostatic complex delivery system formed by ε-PL and whey protein can be used to maintain the stability of ε-PL and solve the problem of limited application of protein-based food. This work aimed to study the interaction between ε-PL and whey protein by multiple characterization methods. The spectroscopy results showed static quenching type and new stretching of C=O for ε-PL-whey protein complexes. Microstructure studies showed that the combination of ε-PL and whey protein made the structure of the complexes become rough and dense. The interaction between ε-PL and whey protein could improve the stability of the complexes system during storage. Additionally, the interaction affected critical gel temperatures and gel texture properties of complexes with change of whey protein concentration, mass ratio of ε-PL to whey protein, pH value in alkaline solutions, and ion concentration. Overall, this study confirmed the interaction between ε-PL and whey protein, and it will provide a reference for the application of ε-PL in protein food matrix.

Influence of polysorbates (Tweens) on structural and antimicrobial properties for microemulsions.

Polysorbates (Tweens) are one of the most used excipients for essential oils encapsulation. In this work, the polysorbate based microemulsions (PMEs) for R-(+)-limonene (LMN) encapsulation were investigated for the structural and antimicrobial properties. PMEs were constructed using the pseudoternary phase diagrams, and then characterized for electrical conductivity, rheology, size distribution and particle geometry. Conductivity and rheological measurement results showed that Tween 80 and Tween 60 based microemulsions have identical phase transitions. Dynamic light scattering demonstrated that hydrodynamic diameters of oil-in-water microemulsions decreased from 30 nm to 25 nm during the dilution, while small-angle X-ray scattering indicated that their spherical geometries were maintained. PMEs exhibited enhanced antimicrobial efficiencies in vitro against Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa. Interestingly, when Tween 80 was replaced by Tween 60, PME was observed more effective against S. aureus. The two PMEs structural analogues exhibited different antimicrobial efficiencies corresponding to the bioactivity of polysorbates. In conclusion, PMEs can be considered as a desirable system for LMN encapsulation to enhance its solubility and antimicrobial efficiency. Furthermore, the difference in the antimicrobial efficiency suggested that the choice of emulsifiers should be concerned to improve further applications.

Mechanism of the antimicrobial activity of whey protein-ε-polylysine complexes against Escherichia coli and its application in sauced duck products.

ε-Polylysine (ε-PL) is a natural and highly effective cationic antimicrobial, of which antibacterial activity is limited in food matrix because of ε-PL's charged amino groups that form complexes with food polyanions. Whey protein-ε-PL complexes delivery system was found to be able to solve the problem and keep the antibacterial activity. This study investigated the antibacterial activity of the complexes and its mechanism against Escherichia coli. The minimal inhibitory concentration of ε-PL was in the range 11.72-25.00 g/mL for the complexes containing different amount of ε-PL and was similar to that of free ε-PL. The results of scanning electron microscopy showed that the complexes could destroy the structure of E. coli cell membrane surface, leaving holes on the surface of the bacteria, leading to the death of the bacteria. The molecular dynamics simulation results showed that the mechanism of the antibacterial activity of the complexes was as follows: under electrostatic interaction, the complexes captured the phospholipid molecules of the bacterial membrane through the hydrogen bonds between the positively charged amino groups of ε-PL and the oxygen atom of the phosphate head groups of the membrane, which could create holes on the surface of the bacteria and lead to the death of the bacteria. The results of activity on real food systems showed that the complexes kept the number of E. coli within 5.8 log10 CFU/g after 7 d storage in sauced duck products, while the positive control (ε-PL) was 6.5 log10 CFU/g and negative control (sterile water) was 7.8 log10 CFU/g. Overall, this study confirmed the antibacterial activity of the complexes and provided fundamental knowledge of its antibacterial activity mechanism.

pH-induced structural transition during complexation and precipitation of sodium caseinate and ε-Poly-l-lysine.

ε-Polylysine (EPL) is a food-grade antimicrobial peptide that forms complexes with proteins. Such complexes are potential carriers for targeted delivery of agents. To elucidate the formation of such complexes, the pH-induced phase transition of EPL and sodium caseinate (SC) complexes were characterized in terms of ionic strengths (I) and EPL/SC weight ratios (r). Electrostatic nanocomplexes (e.g. r = 2-3, I = 2 mM) were formed near the isoelectric point of SC using turbidimetry, dynamic light scattering, and ζ-potential measurements. Phase analyses revealed that the formation of nanocomplexes primarily depends on the I, and saturated binding was recorded above r = 2-2. Electrostatic potential modelling of EPL was employed to describe the interaction affinity. A three-dimensional phase boundary curve was established which divided the complexation into a nano-scale and phase separation. Atomic force microscopy images confirmed that nanocomplexes were spherical particles with uniform shapes. Morphologic examination using optical and scanning electron microscopy and Fourier transform infrared spectroscopy revealed that the nanocomplexes formed "sponge-like" precipitates at larger length scales. This work reveals the possible mechanism that drives the complexation of sodium caseinate and ε-Poly-l-lysine. This is expected to guide the construction of tailor-made protein complexes in industrial applications.

Physicochemical properties and formation mechanism of electrostatic complexes based on ε-polylysine and whey protein: Experimental and molecular dynamics simulations study.

ε­Polylysine (ε-PL) is a new natural food-grade antimicrobial that has been widely applied in the food and beverage industry. This study characterized the physicochemical properties of an electrostatic complex of the ε-PL and whey protein at different whey protein-to-ε-PL mass ratios, pH, and ionic strength by using the turbidity measurements, size and zeta potential measurements. The interaction and formation mechanism of the electrostatic complexes are explored by analysis of the hydrogen bonds and ion pairs, hydrophobic and hydrophilic solvent assessable surface area and secondary structure using molecular dynamics simulations. The experimental results showed that the ε-PL bound to the surface of whey protein forming an electrostatic complex which could be either soluble or insoluble depending on the whey protein-to-ε-PL mass ratios, pH, and ionic strength. The molecular dynamics simulations results showed that conformational rearrangements of α­lactalbumin and bridging effect of ß­lactoglobulin occurred. The interaction was mostly driven by the hydrogen bonds and ion pairs, which mainly occurred in the hydrophilic part of the whey protein surface. This study provides the theoretical basis that will facilitate more rational application of ε-PL in the food matrix.

Effects of Different Acyl Gellan Gums on the Rheological Properties and Colloidal Stability of Blueberry Cloudy Juice.

In this study, gellan gums with different acyl contents were prepared, and their effects on blueberry cloudy juices were compared. The rheological properties, stability coefficients, sedimentations, color parameters and particle size distributions of blueberry cloudy juices with 0.035% (w/w) of gellan gum were measured. As the acyl content increased, the viscosity increased, and the sedimentation and stability coefficient values decreased. Gellan gums with higher acyl contents provided better beverage stabilizing capabilities through stricter enforcement of the molecular associations. Overall, this study provides valuable information for enhancing the gelation and stabilization of blueberry cloudy juices, confirms the superiority of high acyl gellan gums for inhibiting the color fading of anthocyanins, and further guides the development of novel product concepts. PRACTICAL APPLICATION: Cloudy juices made from blueberries have many benefits. However, the particles in cloudy juices will flocculate during storage, resulting in an undesirable precipitate. In our work, gellan gums with different acyl contents were prepared and applied to blueberry juice to prevent aggregation. The results provide valuable information for enhancing the stabilization of blueberry juices, confirm the superiority of high acyl gellan for inhibiting color fading, and further guide the development of novel product concepts.

Antioxidant and hypolipidemic effects of soymilk fermented via Lactococcus acidophilus MF204.

Previous studies have shown that fermentations can enhance the bioactivity and absorption rate of soybean products. Fermented soybean products can alleviate hyperlipidemia and decrease risks of atherosclerosis and cardiovascular diseases. This study aimed to investigate the effects and mechanisms of soymilk fermented by Lactococcus acidophilus on blood lipids and antioxidant enzyme activities of rats fed with a high fat diet. Sixty rats were randomly assigned to six groups: normal control group (NC), high-fat control group (HFC), positive control group (cholestyramine, PC), Lactococcus acidophilus group (LA), soymilk group (SM), and fermented soymilk group (FSM), respectively. The NC group was fed with a basic diet, while the other groups were fed with a high-fat diet. After the experimental period (6 W), rats were sacrificed by decapitation. Blood and liver were collected to measure the concentrations of lipids and antioxidant enzyme activities. Results demonstrated that fermented soymilk could regulate lipid levels, restore HDL-c and TG to normal levels, and lower the concentrations of LDL-c than hypolipidemic drugs in hyperlipidemia rats. More importantly, fermented soymilk caused significant reduction in arteriosclerosis index and coronary risk index. Fermented soymilk also improved antioxidant capacities of hyperlipidemia rats. The increase of aglycone isoflavones in fermented soymilk could explain the above phenomena. In conclusion, soymilk fermented by Lactococcus acidophilus reduced risks of arteriosclerosis and coronary heart disease by regulating lipid levels and improving the antioxidant capacities of hyperlipidemia rats.

Effects of cellulose derivative hydrocolloids on pasting, viscoelastic, and morphological characteristics of rice starch gel.

Effects of sodium carboxymethyl cellulose (CMC) and hydroxypropyl methyl cellulose (HPMC) on the pasting, viscoelastic, and morphological properties of rice starch gel were studied. The addition of CMC increased the peak and trough viscosities, while decreased the final and setback viscosities of rice starch. The peak and trough viscosities of rice starch gel were only little affected by the addition of HPMC. The dynamic viscoelastic result showed that the addition of CMC significantly increased the values of storage modulus (G') and loss modulus (G″), while reduced the value of tanδ as compared to the control sample. Only a small increase in values of G' and G″ was observed in the case of HPMC. The rice starch gel with CMC addition exhibited higher resistances to the stress and produced a stronger gel network. The creep recovery data were well fitted by a four-element Burger's model. Furthermore, the morphological characteristics were in agreement with the finding of rheological results. It was concluded that the addition of CMC and HPMC modified the rheology of rice starch gel in different ways and interacted under different models based on their molecular structures. PRACTICAL APPLICATIONS: Gluten-free foods such as rice cake are essential for people who suffer from celiac disease which is a digestive disorder caused by the consumption of grains containing gluten. The use of CMC and HPMC represents the most widespread approach used to mimic gluten in the manufacture of gluten-free breads based on rice starch, due to their structure-building and water-binding properties. Therefore, it is necessary and crucial to investigate the physical-chemical properties such as pasting and rheological properties of the rice starch with these hydrocolloids. In addition, a better understanding of the interactions of CMC and HPMC on the rice starch could provide additional tools for selection of gluten free recipes with improved rheological and textural properties.

Physicochemical and antimicrobial properties of ε-polylysine/carboxymethyl chitosan polyelectrolyte complexes and their effect against spoilage microorganisms in raw pork.

This study investigated the properties of polyelectrolyte complexes (PECs) fabricated by using ε-polylysine (EPL) and N,O-carboxymethyl chitosan (NOCC) and their potential applications in raw pork. The phase behaviors of PECs in aqueous solutions are characterized by the ζ-potential, mean radius and turbidimetric measurements. Stable colloidal and soluble PEC systems can be fabricated by carefully adjusting the mass ratio of NOCC to EPL. The minimum inhibitory concentration (MIC) assay showed that the colloidal and soluble PECs could maintain the antimicrobial activity of EPL in a laboratory medium. The antimicrobial effectiveness of coatings incorporating three PECs against spoilage microorganisms of raw pork under refrigerated conditions (4 °C) was evaluated. Microbial analysis demonstrated that the bacterial counts were significantly (P < 0.05) lower in sprayed samples with tested PECs containing 0.1% (v/v) EPL, especially for PECs with the mass ratio (NOCC/EPL) at 3 than that of the control sample throughout the storage period, while there were not significantly different counts (P > 0.05) among all samples in the case of molds and yeasts.

Effect of sucrose fatty acid esters with different hydrophilic-lipophilic balance values on pasting and rheological properties of waxy rice flour.

Effects of sucrose fatty acid esters (SEs) with hydrophilic-lipophilic balance (HLB) values of 5 (S-570), 9 (S-970), and 15 (S-1570) on the pasting and rheological properties of waxy rice flour (WRF) were investigated. Rapid Visco Analyzer (RVA) showed that addition of SEs affected the pasting properties of WRF. Rheological experiment includes the steady shear flow characteristics, and dynamic viscoelastic properties were also determined using a controlled-stress rheometer. The steady shear tests demonstrated that the viscosity data fitted well with the power law model (R 2≥0.976) and all WRF pastes exhibited typical pseudoplastic and shear-thinning properties. Dynamic rheological measurements revealed that the addition of S-970 and S-1570 significantly increased the values of G' and G″ of samples, whereas the addition of S-570 decreased these values. The addition of S-1570 reduced the value of tanδ, whereas S-570 and S-970 increased it.