Ru Liu

Role of secondary structures in the gelation of porcine myosin at different pH values

Secondary structures, gelation properties and their relationships in porcine myosin were studied by circular dichroism, dynamic rheological measurement and scanning electron microscopy. Gelling of porcine myosin involved a change in myosin conformation with protein-protein and protein-water interactions. The gelation properties were strongly pH and temperature dependent. Near the pI (pH 5.5 and 6.0), porcine myosin could spontaneously coagulate at 15°C resulting partially from the presence of more β-sheets. Myosin at pH6.5-9.0 began to form a gel at temperatures greater than 38°C. Heating caused α-helices to partially turn into β-sheets and random coils. Subsequently, myosin aggregated and formed a gel network. The gel strength decreased and the water-holding capacity (WHC) increased with increasing pH. Correlation analysis indicated that both the unfolding of α-helices and the formation of β-sheets favored the gelation of porcine myosin. A high β-sheet fraction prior to heating resulted in a low WHC of resultant gel. A compact and uniform gel was also obtained at pH6.5.

Effects of salts on the gelatinization and retrogradation properties of maize starch and waxy maize starch

The objective of this study was to evaluate the effects of salts on the gelatinization and retrogradation of maize and waxy maize starch. Experimental results showed that the salting-out or structure-making ions, such as F(-) and SO4(2-), decreased the swelling power, solubility and transparency of both starches, but increased the gelatinization temperature, enthalpy, and syneresis, due to the tendency of these ions to protect the hydrogen bond links among starch molecules. On the other hand, the salting-in or structure-breaking ions, such as I(-) and SCN(-), exhibited the opposite effects. Microscopic observations confirmed such effects of salts on both starches. Furthermore, the effects of salts were more significant on waxy maize and on normal maize starch. Generally, salts could significantly influence on the gelatinization and retrogradation of maize and waxy maize starch, following the order of the Hofmeister series.

Heat-induced denaturation and aggregation of actomyosin and myosin from yellowcheek carp during setting

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.

Effects of Ozone Treatments on the Physicochemical Changes of Myofibrillar Proteins from Silver Carp (Hypophthalmichthys molitrix) during Frozen Storage

Physicochemical changes of myofibrillar proteins from silver carp surimi during frozen storage as affected by two manners of ozone treatments were investigated. For preparation of surimi treated with ozone, ozone water (8 mg/L) was used in either the first (To1) or the second (To2) cycle of rinsing. As compared with control samples (Tc) (rinsing two cycles with water), myofibrillar proteins from To1 surimi showed slightly lower free sulfhydryl contents and higher surface hydrophobicity throughout frozen storage and lower Ca2

Effects of high intensity unltrasound on structural and physicochemical properties of myosin from silver carp

Myosin from silver carp was sonicated with varying power output (100, 150, 200 and 250W) for 3, 6, 9, and 12min. The changes in the structure and physicochemical properties of myosin were evaluated by dynamic light scattering, SDS-PAGE and some physicochemical indexes. The ultrasound treatments induced a significant conversion of myosin aggregates to smaller ones with a more uniform distribution, and obvious enhancement in solubility. The structure of myosin was also notably changed by sonication, with a decrease in Ca2+-ATPase activity and SH content, and an increase in surface hydrophobicity. Furthermore, SH groups were oxidized, leading to a decrease in reactive SH and total SH contents. SDS-PAGE analysis revealed that ultrasound could induce the degradation of myosin heavy chain and change the protein fraction of myosin. Collectively, the ultrasonic treatment of 100W for 3min showed slight influence on the SH content, S0-ANS, and electrophoretic patterns, and the extent of changes in myosin structure and physicochemical properties tended to increase with ultrasonic power and time. The integrated data indicate that ultrasonic treatment can facilitate the improvement of the solubility and dispersion of myosin, but the choice of a suitable ultrasonic condition to avoid oxidation and degradation of myosin is very important.

Gelling Properties of Fish/Pork Mince Mixtures.

The gel properties of silver carp/pork mince mixtures were investigated as well as the protein structural changes and interactions during gelling using rheology, SEM, and FT-Raman spectroscopy. The breaking force values for gels containing 0% to 40% pork was significantly lower (P < 0.05) compared with gels containing 50% to 100% pork. Gels containing 70% to 100% pork had significantly higher (P < 0.05) breaking force values compared with gels containing 50% to 60% pork. Deformation values were more mixed. Dynamic rheological data suggested that mixing fish and pork at 3:7 could strengthen the gel network. The addition of 40% pork or above, significantly decreased (P < 0.05) the water retention of the gels compared with the 100% fish gels. The dimensional ordering of gels was also reduced by addition of pork. The reduced ordering was one of the reasons for the low water retention for fish/pork mixed gels. Raman spectral analysis confirmed that mixing fish and pork in 7:3 and 3:7 ratios could promote hydrophobic interactions such as bringing tyrosine residues into the intermolecular interface. The interactions in the 3:7 fish/pork mixed gels were favorable for forming a stronger gel. However, the interactions in the 7:3 fish/pork mixed gels were adverse. The water retention of gels was related to both molecular interactions and secondary structures of protein as well as the microstructure of the gels.

Effects of the Acid- and Alkali-Aided Processes on Bighead Carp (Aristichthys nobilis) Muscle Proteins

The objective of this study was to investigate the effects of the acid- and alkali-aided processes on bighead carp (Aristichthys nobilis) muscle protein as compared with the conventional washing method. Acid- and alkali-aided processes resulted in higher protein recoveries than conventional washing method. In textural profile analyses, the highest hardness and cohesiveness were observed in the gels prepared by conventional washing and alkali-aided processing (p < 0.05). No endothermic peak was found in the differential scanning calorimetry thermogram of protein isolates after acid- and alkali-aided processes. The hydrophobic interactions and disulfide bonds were the main chemical bonds to maintain the stability of the gel matrix, while the sulfhydryl group in bighead carp muscle was apt to be activated during alkali-aided processing. The α-helical content of actomyosin decreased remarkably after the acid- and alkali-aided processes (p < 0.05). Overall, there is a potential to apply the alkali-aided processing to extract proteins from bighead carp muscle for the production of surimi-based seafoods.

Insights into the rheological behaviors evolution of alginate dialdehyde crosslinked collagen solutions evaluated by numerical models

The elaboration of the rheological behaviors of alginate dialdehyde (ADA) crosslinked collagen solutions, along with the quantitative analysis via numerical models contribute to the controllable design of ADA crosslinked solution systems fluid mechanics performance during manufacturing process for collagen biomaterials. In the present work, steady shear flow, dynamical viscoelasticity, creep-recovery, thixotropy tests were performed to characterize the rheological behaviors of the collagen solutions incorporating of ADA from the different aspects and fitted with corresponding numerical models. It was found that pseudoplastic properties of all samples enhanced with increasing amounts of ADA, which was confirmed by the parameters calculated from the Ostwald-de Waele model, Carreau and Cross model, for instance, the non-Newtonian index (n) decreased from 0.786 to 0.201 and a great increase by 280 times in value of viscosity index (K) was obtained from Ostwald-de Waele model. The forth-mode Leonov model was selected to fit all dynamic modulus-frequency curves due to its higher fitting precision (R2>0.99). It could be found that the values of correlation shear viscosity (ηk) increased and the values of relaxation time (θk) decreased with increasing ADA at the fixed k value, suggesting that the incorporation of ADA accelerated the transformation of the collagen solutions from liquid-like to gel-like state due to more formation of CN linkages between aldehyde groups and lysine residues. Also, the curves of creep and recovery phase of the native and crosslinked collagen solutions were simulated well using Burger model and a semi-empirical model, respectively. The ability to resist to deformation and elasticity strengthened for the samples with higher amounts of ADA, accompanied with the important fact that compliance value (J50) decreased from 56.317Pa-1 to 2.135Pa-1 and the recovery percentage (Rcreep) increased from 2.651% to 28.217%. Finally, it was found that the area of thixotropic loop increased from 8.942Pa/s to 17.823Pa/s with increasing introduction of ADA, suggesting that stronger thixotropic behavior was associated with higher amount of ADA. Furthermore, Herschel-Bulkley model was employed to describe the up and down curves of all samples and it was confirmed that all collagen solutions belonged to pseudoplastic fluid (the flow index<1) without apparent yield stress and shear-thinning behaviors were more obvious with increasing additions of ADA according to the increasing consistency coefficient K values. Overall, this work contributed a new insight into the interactions between collagen and ADA based on quantitative rheological methods reflecting the different rheological properties and the results obtained should be of great utility in the extensive application of ADA crosslinked collagen solutions into diverse collagen-based materials.

Comparison of Conventional Washing Processing and pH Shift Processing on Gelation Characteristics of Bighead Carp (Aristichthys nobilis) Muscle Proteins

ABSTRACT In this study, gelation characteristics of bighead carp (Aristichthys nobilis) protein isolates prepared by pH shift processing were investigated as compared with those of surimi prepared by conventional wash processing. Results showed that the gel from alkali-aided protein isolate exhibited a higher breaking force than that from conventional washed surimi (p < 0.05). However, the gel from conventional washed surimi had higher whiteness (p < 0.05) and lower expressible moisture (p < 0.05). The rheological study showed that protein isolates exhibited different storage modulus and loss tangent patterns from conventional washed surimi during heating. Acid-aided processing could lead to higher denaturation and dissociation for fish muscle myosin and a coarser gel network from the sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) pattern and the scanning electron microscopy (SEM). Overall, there is a potential to apply pH shift processing, especially alkali-aided processing, to extract more proteins from bighead carp muscle for the production of surimi-based food.