Siming Zhao

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.

Effects of concurrent ball milling and octenyl succinylation on structure and physicochemical properties of starch

This work concerns the effects of concurrent ball milling (BM) and octenyl succinic anhydride (OSA) modification on the starch microstructure and physicochemical properties (swelling, emulsifying, and rheological). Unlike normal OSA-modified starches, the BM/OSA-modified starch displayed new features such as reduced viscosity and rigidity but increased paste stability during shearing, heating and cooling, regardless of the substitution degree. More interestingly, while the physicochemical properties could be regulated by simply altering the BM treatment time, BM/OSA was more efficient and effective at modulating starch properties during the initial period (approx. 10h), as seen by the rapid evolutions in starch structural disruption and OSA esterification. Thus, the BM/OSA modification can serve as a viable and cost-effective approach for producing octenyl succinate starches where low viscosity (at relatively high concentrations) and high paste stability are desired.

Gel characteristics and microstructure of fish myofibrillar protein/cassava starch composites

The changes in fish myofibrillar protein/cassava starch composites in the starch fraction range from 0 to 1, with their total content maintained at 60mg/mL, were investigated in terms of textural properties, rheological behaviours, morphology, spatial distribution and protein molecular structure. The results revealed that the starch fraction of 0.5 was a critical point for the conversion of the protein matrix to starch matrix and conversion of the gel from elastic to weak. Moreover, the protein-starch synergistic effect on the storage modulus was strongest at fractions of 0.5 and 0.6, due to the formation of a semi-interpenetrating network, with more amylose from the melted starch granules interpenetrated with the protein molecules, and the absorption of water by the starch granules to concentrate the protein matrix. Additionally, no covalent interaction between the protein and starch occurred with increasing starch fraction, thus having no significant influence on the protein secondary structure.

Characterization of cationic starch flocculants synthesized by dry process with ball milling activating method

The cationic starch flocculants were synthesized by the reaction of maize starch which was activated by a ball-milling treatment with 2,3-epoxypropyl trimethyl ammonium chlorides (ETMAC) using the dry method. The cationic starches were characterized by several approaches including scanning electron microscope (SEM), degree of substitution (DS), infrared spectrum (IR), X-ray diffraction (XRD), flocculating activity, electron spin resonance (ESR), and solid-state nuclear magnetic resonance (NMR). The effect of mechanical activation on starch etherifying modification was investigated. The mechanical activation cracked starch granules and destructed their crystal structures. This resulted in enhancements to the reaction activity and reaction efficiency, which was approved by ESR and solid state NMR. The starch flocculants, synthesized by the reaction of mechanically activated starches at 90°C for 2.5h with ETMAC at molar ratio of 0.40:1.00, showed good flocculation activity. The substitution degree (0.300) and reaction efficiency (75.06%) of starch flocculants synthesized with mechanically activated starches were significantly greater than those of starch flocculants with native starches (P<0.05).

Microstructural, textural, and sensory properties of whole-wheat noodle modified by enzymes and emulsifiers.

With the utilization of enzymes including endoxylanase, glucose oxidase (GOX) and transglutaminase (TG), and emulsifiers comprising sodium stearoyl lactate (SSL) and soy lecithin, the microstructural, textural, and sensory properties of whole-wheat noodle (WWN) were modified. The development time and stability of whole-wheat dough (WWD) were enhanced by TG due to the formation of a more compact gluten network, and by SSL resulting from the enhanced gluten strength. Microstructure graphs by scanning electron microscopy (SEM) verified that TG and SSL promoted the connectivity of gluten network and the coverage of starch granules in WWN. TG increased the hardness and elasticity of cooked WWN, while two emulsifiers increased the noodle cohesiveness. Additionally, TG and SSL improved the sensory properties of noodle such as bite, springiness, and mouth-feel. The results suggest that TG and SSL are effective ingredients in enhancing the gluten strength of WWD and improving the qualities of WWN.

Hydration-induced crystalline transformation of starch polymer under ambient conditions

With synchrotron small/wide-angle X-ray scattering (SAXS/WAXS), we revealed that post-harvest hydration at ambient conditions can further alter the starch crystalline structure. The hydration process induced the alignment of starch helices into crystalline lamellae, irrespective of the starch type (A- or B-). In this process, non-crystalline helices were probably packed with water molecules to form new crystal units, thereby enhancing the overall concentration of starch crystallinity. In particular, a fraction of the monoclinic crystal units of the A-type starches encapsulated water molecules during hydration, leading to the outward movement of starch helices. Such movement resulted in the transformation of monoclinic units into hexagonal units, which was associated with the B-type crystallites. Hence, the hydration under ambient conditions could enhance the B-polymorphic features for both A-type and B-type starches. The new knowledge obtained here may guide the design of biopolymer-based liquid crystal materials with controlled lattice regularity and demanded features.

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.

Cadmium Removal from Rice by Separating and Washing Protein Isolate

In this study detoxification of 3 Chinese Cd-contaminated cultivars (Jinyou463, Yuchi, and Xiangzaoxian 32) of rice was explored. By separation with an alkaline method, Cd concentrations of the starch isolates were decreased from 0.2769, 0.4037, and 0.5156 mg/kg in starting milled rice to 0.1056, 0.1585, and 0.1923 mg/kg, respectively. However, the Cd concentrations reached up to 2.5905, 3.1628, and 4.8593 mg/kg in the protein isolates, respectively. Therefore, 10 common acids in food industry were investigated to remove Cd from protein isolate by washing process. The optimal washing conditions were 0.5 M citric acid, acid to rice protein isolate ratio of 6:1 v/w, shaking time of 1 h at room temperature. The rice protein isolate showed a significant decrease in Cd concentration and the removal efficiency was more than 95% after 2 washings at optimized conditions. Rice proteins were not degraded at all and had very little loss during citric acid washing process. The study presents a promising way of depurating Cd-contaminated rice, and meanwhile it reduces the risk of heavy metal causing food safety issues effectively.

Chemical structure and antioxidant activity of the biomacromolecules from paddlefish cartilage.

To evaluate the effect of extraction methods on chemical structure and association with antioxidant activity of the extracts from paddlefish cartilage, the three extracts (EXT-A, EXT-B and EXT-C) were obtained from the cartilage by signal alkali extraction, microwave-assisted alkali extraction, and microwave-assisted alkali extraction followed by Sevags deproteinization, respectively. Chemical structures of the polymer were investigated by GPC (Gel Permeation Chromatography), FT-IR, GC and amino acid analysis. The results indicated that both EXT-A and EXT-B consisted of polysaccharide and protein, but the protein content of EXT-B (87.9%) was significantly higher than EXT-A (22.3%). Meanwhile EXT-C was polysaccharide composed of glucose, galactose, D-glucuronic acid and xylose. EXT-B extracted by microwave-assisted alkali method, containing dominant protein and rich in tyrosine, glycine and glutamic acid, exhibited obviously higher antioxidant activity than those of the extracts by other methods. The results indicated that microwave-assisted alkali extraction was favorable for protein dissolving out of cartilage, and protein content and composition of the extracts play important roles in antioxidant activity.