Xianchao Feng

Effects of ultrasonic processing on caspase-3, calpain expression and myofibrillar structure of chicken during post-mortem ageing

In this investigation, ultrasonic treatments at a frequency of 40 kHz and power of 1,500 W made caspase-3 and calpain activities significantly higher in chicken muscle after slaughter during 5d storage (p<0.01). Additionally Western blotting analysis of α-spectrin showed that ultrasonic treatments caused the production of α-spectrin degradation products of 120 and 150 kDa more dense than the control (p<0.01). Degradation of calpastatin during chicken meat ageing was induced by ultrasound treatments (p<0.01), which suggested the ability of caspase-3 to cleave calpastatin. SDS-PAGE showed that all treatments enhanced accumulation of the 30 kDa troponin-T degradation product (p<0.01), and transmission electron microscopy images of myofibrils displayed that damage of ultrasound treatment for 60 min was more extensive than at 30 min. The findings proved the low-frequency and high power ultrasonic treatments improved disruption of myofibrillar structures and increased proteolysis of chicken meat faster by triggering an apoptosis cascade.

Characterization of Bacterial Cellulose by Gluconacetobacter hansenii CGMCC 3917.

In this study, comprehensive characterization and drying methods on properties of bacterial cellulose were analyzed. Bacterial cellulose was prepared by Gluconacetobacter hansenii CGMCC 3917, which was mutated by high hydrostatic pressure (HHP) treatment. Bacterial cellulose is mainly comprised of cellulose Iα with high crystallinity and purity. High-water holding and absorption capacity were examined by reticulated structure. Thermogravimetric analysis showed high thermal stability. High tensile strength and Youngs modulus indicated its mechanical properties. The rheological analysis showed that bacterial cellulose had good consistency and viscosity. These results indicated that bacterial cellulose is a potential food additive and also could be used for a food packaging material. The high textural stability during freeze-thaw cycles makes bacterial cellulose an effective additive for frozen food products. In addition, the properties of bacterial cellulose can be affected by drying methods. Our results suggest that the bacterial cellulose produced from HHP-mutant strain has an effective characterization, which can be used for a wide range of applications in food industry.

Susceptibility of whey protein isolate to oxidation and changes in physicochemical, structural, and digestibility characteristics

Oxidation is an important factor for denaturing of whey protein isolate (WPI) during food processing. We studied the effects of chemical oxidation on physicochemical and structural changes along with in vitro digestibility of WPI in this work. Evaluation of physicochemical changes showed that carbonyl level and dityrosine content increased, whereas total and free thiol group levels decreased for oxidized WPI samples. For the structural changes, protein aggregation was measured by surface hydrophobicity, turbidity, and particle diameter, which was increased for oxidized WPI samples. The increase of the secondary structure β-sheets and antiparallel β-sheet also supported the aggregation of oxidized WPI. A direct quantitative relationship between physicochemical and structural changes and protein digestibility indicated that oxidation-related damage restricts the susceptibility of WPI to proteases. In conclusion, WPI had high susceptibility to oxidative stress, and both physicochemical and structural changes caused by severe oxidative stress could decrease the rate of in vitro digestibility of WPI.

Evaluation of antioxidant capacity and flavor profile change of pomegranate wine during fermentation and aging process

Antioxidant properties and flavor characteristic profile of pomegranate wine during winemaking were investigated. The total phenol content and radical scavenging activity exhibited a slightly decrease in the end edge. Punicalagins and gallic acid were revealed to be the most abundant phenolic compounds, followed by ellagic acid and vanillic acid. These constituents were mainly responsible for the effective antioxidant capacity of pomegranate wine. The major changes of flavor qualities occurred in the initial stage, particularly 0-4day of fermentation. Fermentation significantly reduced the relative content of aldehydes, ketones, heterocyclic and aromatic compounds, but promoted the generation of esters and alcohols. This is the first time of using E-nose and E-tongue to monitor odour and taste changes in the brewing process of pomegranate wine. The study may provide a promising instruction for improving functional features and quality control of the pomegranate wine.

Physical properties and antioxidant capacity of chitosan/epigallocatechin-3-gallate films reinforced with nano-bacterial cellulose

Films with antioxidant activity were prepared by combining chitosan (CH) and epigallocatechin-3-gallate (EGCG) with nano-bacterial cellulose (BC) as a reinforcement agent. Results showed that BC addition improved the qualities of films jeopardized by EGCG. Fourier Transform Infrared (FTIR) spectroscopy analysis confirmed that there were intermolecular interactions among BC, CH and EGCG though hydrogen bonding. Consequently, BC addition increased the crystallinity and thermal stability of CH-BC5/10-EGCG15/30 films analyzed by X-ray diffraction (XRD) and thermogravimetric (TGA) analysis. BC addition also significantly decreased water solubility (WS), from 26.54% to 20.80%, increased tensile strength (TS), from 18.71 to 44.17MPa, and increased elongation at break (EAB), from 2.72% to 7.34%. Moreover, BC and EGCG had high affinity for each other, as BC addition lowered the release of EGCG from CH films with a higher ABTS radical scavenging ability. Therefore, BC can be used as a sustained release carrier of EGCG in antioxidant active films.

Effects of NaCl Concentration and Potassium Chloride Substitutions on the Thermal Properties and Lipid Oxidation of Dry-Cured Pork

The thermal properties of cured meat are important for determining storage life and nutritional quality. However, few studies have focused on the thermal properties of dry-cured pork, particularly in relation to salt level and type. In order to study the thermal properties of dry-cured pork, we used differential scanning calorimetry (DSC) to evaluate the net heat energy (enthalpy, ΔH), onset (T(onset)), and maximum (T(max)) temperatures of different pork cuts salted with mixtures of chloride (NaCl and KCl) salts within the curing and ripening temperature range. Within the curing temperature range (-5 to 20 °C), the T(onset), T(max), and ΔH of cured meat treated with different NaCl : KCl mixtures were generally lower than for fresh meat, which indicates that the addition of NaCl or KCl can reduce the melting of lipids and water (especially lipids), in different pork cuts. Within the ripening temperature range (5 to 50 °C), heat absorption peaks in belly and leg cuts were between 29 and 33 °C. However, no obvious heat absorption peak was found in loin cuts. Compared to non-KCl substitutions, a slightly higher KCl substitution could significantly (P < 0.05) enhance ΔH values of dry-cured belly and leg cuts. The likely cause of this phenomenon is that high KCl substitutions promote lipid oxidation (r = 0.98, for belly; r = 0.95, for leg cuts). Therefore, KCl substitution should be no more than 30% (wt/wt), especially for high lipid pork, to prevent excessive melting and oxidation of lipids during the dry-curing process.

Dose-dependent effects of rosmarinic acid on formation of oxidatively stressed myofibrillar protein emulsion gel at different NaCl concentrations

The effects of rosmarinic acid (RA) (12, 60 and 300μM/g protein) on the textural properties and stability of oxidized myofibrillar protein (MP) emulsion gels were investigated. A low dose (12µM/g) of RA significantly prevented the loss of thiol and ε-NH2 groups and the unfolding of the oxidized MP. However, a high dose of RA (300µM/g) covalently and non-covalently interacted with the MPs, which induced a significant loss of thiol and ε-NH2 groups and aggregation of the MPs, causing decreased solubility, resulting in a poor three-dimensional emulsion gel network, and hence, higher cooking loss and lower gel strength. Moreover, the emulsifying properties of the MP emulsion gel were jeopardized by 300µM/g RA. A high concentration of NaCl (0.6M) enhanced the interaction between RA and MPs, increasing deterioration of the internal structure and leading to extremely unstable emulsifying properties of the MP emulsion gel.

Incorporated glucosamine adversely affects the emulsifying properties of whey protein isolate polymerized by transglutaminase

Glucosamine (GlcN) and microbial transglutaminase (Tgase) are used separately or together to improve the emulsifying properties of whey protein isolate (WPI). However, little is known about how the emulsifying properties change when GlcN residues are incorporated into WPI cross-linked by Tgase. We used Tgase as a biocatalyst to cross-link WPI in the presence of GlcN in a liquid system for 12 h at a moderate temperature (25°C). Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analyses indicated that protein polymerization and GlcN conjugation occurred simultaneously, phenomena also supported by the loss of free amines (9.4-20.5%). Addition of 5 U Tgase/g protein improved the emulsifying properties of moderately cross-linked WPI polymers. The Tgase-treated WPI polymers had a larger particle size (∼2.6-fold) than native WPI, which may have reduced coalescence and flocculation in an oil-in-water emulsion system. However, the incorporation of GlcN residues into WPI, predominantly via enzymatic glycation, partly inhibited the cross-links between the WPI molecules catalyzed by Tgase, reducing the size of the WPI polymers 0.81- to 0.86-fold). Consequently, WPI+GlcN conjugates provided less stability to the emulsion. Moreover, high NaCl concentration (0.2 M) decreased the emulsifying properties of the WPI+GlcN conjugates by neutralizing negative electric charges in the glycoconjugates. However, the improved emulsifying properties of WPI cross-linked by Tgase may be useful in food processing at higher NaCl concentrations due to the formation of the thicker steric barrier at the oil-water interface.

Inhibition of Epigallocatechin-3-gallate/protein interaction by methyl-β-cyclodextrin in myofibrillar protein emulsion gels under oxidative stress

Nowadays, natural antioxidants abundant in polyphenols have been widely used to substitute synthetic antioxidants in meat products. In general, high doses of natural antioxidants are required to provide comparative antioxidant effects as synthetic antioxidants. Noticeably, the qualities of meat products can be jeopardized due to interactions between polyphenols and myofibrillar proteins (MPs). In this study, methyl-β-cyclodextrin was used to increase the polyphenol loading amount by preventing interactions between polyphenols and proteins. Solubility, electrophoresis, fluorescence spectroscopy, and surface hydrophobicity analyses indicated that methyl-β-cyclodextrin could dose-dependently inhibit epigallocatechin-3-gallate-induced attacks on MPs under oxidative stress. Gel strength, cooking loss, confocal laser scanning microscopy, dynamic rheological testing, and Raman spectrum during gelation were further analyzed to investigate the effects of methyl-β-cyclodextrin on the qualities of epigallocatechin-3-gallate-treated emulsion gel. Methyl-β-cyclodextrin addition prevented modification of the secondary structure of MPs caused by epigallocatechin-3-gallate. In consequence, the gel and emulsifying properties of MPs were significantly improved. Moreover, β-cyclodextrins could partly inhibit oxidative attacks on MPs and thus increase their solubility. These results indicated that methyl-β-cyclodextrin addition effectively enhanced epigallocatechin-3-gallate loading capacity in meat products.

Development and characterization of agar-based edible films reinforced with nano-bacterial cellulose

Nano-bacterial cellulose (BC), as a reinforcing agent, was used to prepare the agar-based edible films. Effects of BC content (0, 3, 5, 8 and 10%, wt% based on the agar) on the rheological properties of film-forming solution (FFS), and on structure, morphology, crystallinity, and thermal properties of films were investigated. Results of rheological and FTIR analyses revealed that interactions between BC and agar were formed through hydrogen bonds. The crystallinity and the thermal stability of films were improved by addition of BC analyzed by XRD and TGA, respectively. Compared with high BC concentrations (8-10%), a good dispersion of BC at low concentrations (3-5%) in the films was observed by SEM. Moreover, BC addition (10%) significantly decreased moisture content (MC), water solubility (WS) and water vapor permeability (WVP) by 60.4%, 13.3% and 25.7%, respectively. The tensile strength (TS) of films increased from 22.10 to 44.51 MPa after addition of BC (0-10%), whereas the elongation at break (EAB) initially increased with increasing BC concentrations (0-5%), and then decreased with further addition of BC (8-10%). Consequently, agar-based edible films reinforced by moderate nano-BC have the potential as a packaging film for food products.