A new insight into the influence of pH on the adsorption at oil-water interface and emulsion stability of egg yolk protein.

This study investigated the impact of varied pH treatments on the structural, emulsification, and interfacial adsorption properties of egg yolk. The solubility of egg yolk proteins decreased and then increased in response to pH changes, with a minimum value (41.95 %) observed at pH 5.0. The alkaline condition (pH 9.0) significantly impacted the secondary/tertiary structure of egg yolk, with the yolk solution displaying the lowest surface tension value (15.98 mN/m). Emulsion stability was found to be optimal when egg yolk was used as the stabilizer at pH 9.0, which corresponded to the more flexible diastolic structure, smaller emulsion droplets, increased viscoelasticity, and enhanced resistance to creaming. At pH 9.0, proteins exhibited a maximum solubility (90.79 %) due to their unfolded conformation, yet the protein adsorption content at the oil-water interface showed relatively low (54.21 %). At this time, electrostatic repulsion between the droplets and the spatial site barrier made by proteins that were unable to efficiently adsorb at the oil-water interface kept the emulsion stable. Moreover, it was found that different pH treatments could effectively regulate the relative adsorption contents of various protein subunits at the oil-water interface, and all proteins except livetin displayed good interfacial adsorption capacity at the oil-water interface.

Interactions between unfolding/disassembling behaviors, proteolytic subfragments and reversible aggregation of oxidized skeletal myosin isoforms at different salt contents.

Myosin filament plays a critical role in water-trapping and thermodynamic regulation during processing of brined muscle foods. The redox state and availability of proteolytic/antioxidant enzymes affected by salt may change the ion-binding capacity of myosin consequently contributing to swelling and rehydration. Thus, this study investigated the impact of different salt content (0%, 1%, 2%, 3%, 4%, 5% NaCl) and oxidation in vitro (10 mM H2O2/ascorbate-based hydroxyl radical (OH)-generating system) on the oxidative stability, solubility/dispersion capacity, chymotrypsin digestibility, aggregation site and the microrheological properties of isolated porcine myosin. The result showed that, brining at 2% salt exposed more sulfhydryl groups and inhibited the formation of disulfide bond, whereby smaller dispersed structure (diameter within 10-50 nm) and higher Ca2+-ATPase activity of the denatured myosin were observed. Accordingly, gel electrophoresis showed that myosin S1 and HMM subunits were highly oxidized and susceptible to reversible assembles. Despite enhanced hydrophobic interactions between swelled myosin at 3% salt content, ≥4% salt greatly promoted the exposure/polarization of tryptophan and cross-linking structures, mainly occurring at myosin S2 portion. The results of micro-rheology proved that oxidized myosin formed a tighter heat-set network following rehydration at high ion strength (≥4% salt), suggesting an increased inter-droplet resistance and macroscopic viscosity. This work is expected to give some useful insights into improved texture and functionality of engineered muscle foods.

Preparation process optimization of pig bone collagen peptide-calcium chelate using response surface methodology and its structural characterization and stability analysis.

In this study, alcalase and neutrase were used in combination to prepare collagen peptides with high calcium binding ability. The optimal conditions for the preparation of peptide-calcium chelate (mass ratio of peptide/calcium of 4.5:1 for 40 min at 50 °C and pH 9) were determined by response surface methodology (RSM), under which a calcium chelating rate of 78.38% was obtained. The results of Ultraviolet-Visible (UV-Vis), fluorescence and Fourier transform infrared (FT-IR) spectra synthetically indicated that calcium could be chelated by carboxyl oxygen and amino nitrogen atoms of collagen peptides, thus forming peptide-calcium chelate. The chelate was stable at various temperatures and pH values, and exhibited excellent stability in the gastrointestinal environment, which could promote calcium absorption in human gastrointestinal tract. Moreover, Caco-2 cell monolayer model was used to investigate the effect of peptide-calcium chelate on promoting calcium absorption. Results showed that peptide-calcium chelate could significantly improve calcium transport in Caco-2 cell monolayer and reverse the inhibition of calcium absorption by phosphate and phytate. The findings provide a scientific basis for developing new calcium supplements and the high-value utilization of pig bone.

Antioxidant enzyme activities are affected by salt content and temperature and influence muscle lipid oxidation during dry-salted bacon processing.

Fresh pork bacon belly was used as material and manufactured into dry-salted bacon through salting and drying-ripening. During processing both oxidative stability and antioxidant enzyme stability were evaluated by assessing peroxide value (PV), thiobarbituric acid reactive substances (TBARS) and activities of catalase, glutathione peroxidase (GSH-Px) and superoxide dismutase (SOD), and their correlations were also analysed. The results showed that all antioxidant enzyme activities decreased (p<0.05) until the end of process; GSH-Px was the most unstable one followed by catalase. Antioxidant enzyme activities were negatively correlated with TBARS (p<0.05), but the correlations were decreased with increasing process temperature. Salt showed inhibitory effect on all antioxidant enzyme activities and was concentration dependent. These results indicated that when process temperature and salt content were low at the same time during dry-salted bacon processing, antioxidant enzymes could effectively control lipid oxidation.