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•Chitosan/pullulan nanofibers were crosslinked by Maillard and Schiff base reaction.•Crosslinked films showed good water resistance, mechanical and thermal properties.•The enhancing ...effects of the two crosslinking methods were compared.
In this study, electrospun chitosan/pullulan composite nanofiber films were crosslinked by two green methods (heating and cinnamaldehyde). With the increase of chitosan content, the morphology results indicated that the nanostructures of thermal crosslinking chitosan/pullulan (TCP) and cinnamaldehyde crosslinking chitosan/pullulan (CCP) nanofiber films became more stable. The decreases in weight loss (83.65 % to 43.85 % for TCP and 23.42 % to 15.58 % for CCP) and the increases in water contact angle (31.8° to 54.1° for TCP and 83.65 % to 43.85 % for CCP) confirmed the improved water stability. The decreases in water vapor permeability indicated that the crosslinking processes significantly improved the barrier properties of the films. Mechanical and thermal properties of TCP and CCP films were enhanced respectively. Furthermore, the corresponding properties of CCP films were more excellent than TCP films. FTIR results indicated the occurrence of Maillard reaction during the thermal crosslinking process and Schiff base reaction during the cinnamaldehyde crosslinking process.
The effects of thawing methods (refrigeration thawing (RT, 4 °C), water immersion thawing (WT, 18 °C), vacuum thawing (VT, 25 °C), ultrasonic thawing (UT, 20 °C) and microwave thawing (MT)) on the ...conformation and gel qualities of myofibrillar protein (MP) obtained from porcine longissimus muscle were investigated. The results showed that MP conformation and gel qualities of porcine longissimus muscles by VT and UT were insignificantly changed compared to fresh meat (FM). A significant decrease in free amino groups of MP from MT illustrated that MT induced protein aggregation and oxidation (P < 0.05). The results of circular dichroism (CD) spectra analysis and fluorescence spectroscopy indirectly proved that thawing can cause protein cross-linking and degradation, secondary structure destruction, non-hydrophilic domain exposed and conformational change of samples. The largest changes in solubility, surface hydrophobicity and particle size were obtained with MT. The effects on the conformation and gel quality of MP were verified during thawing process.
•The effect of five thawing methods on gel quality of protein was compared.•Gel forming ability of protein has no obvious changes during novel thawing process.•The change of gel quality is induced by protein structural modification.
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•Quality of patty during frozen storage was verified by WHC, a*, hardness.•Oxidation in patty during frozen storage was confirmed by TBARS and carbonyl content.•Changes in protein ...structure were measured by the fluorescence intensity.•Correlations among quality, protein oxidation and structure were analyzed by PCA.
Changes in quality, protein structure and oxidative reactions of quick-frozen pork patties (after −30 °C, 30 min), which were frozen at −8 °C, −18 °C, −25 °C, −8/−18 °C (stored at −8 °C for 5 days, then stored at −18 °C for 5 days, storage cycle continue until the end of storage period), −18/−25 °C (the same process as −8/−18 °C, temperature is −18 °C and −25 °C) for 0, 1, 2, 3, and 6 months were investigated. The a*-value, pH, water holding capacity and texture properties of pork patties were significantly changed (P < 0.05) at −8 °C, −8/−18 °C, −18/−25 °C after 1 month of frozen storage. The water redistribution within the patties was detected by LF-NMR analyses. After 6 months of frozen storage, the TBARS and carbonyl content of samples frozen at −8/−18 °C increased by 444% and 239%, respectively. Meanwhile, a decrease in fluorescence intensity reflected a decline in protein structure integrity. The association among quality, oxidative reactions and protein structure were elucidated by principal component analysis. The quality deterioration of the pork patties may be induced by the oxidative reaction and destruction of protein structural integrity during frozen storage.
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•The assembly behavior of myosin molecules limits the development of interfacial proteins.•High-intensity ultrasound (HIU) disrupted the filamentous myosin structure.•HIU improved the ...physical stability of myofibrillar protein (MPs) emulsion.•HIU pretreatment promoted the adsorption and rearrangement of MPs at the O/W interface.•HIU pretreatment enhanced the inter-droplet interactions.
The specific molecular behavior of myofibrillar proteins (MPs) in low-salt media limits the development of muscle protein-based emulsions. This study aimed to evaluate the potential of high-intensity ultrasound (HIU; 150, 300, 450, and 600 W) to improve the physical stability of MP emulsion at low ionic strength and decipher the underlying mechanism. According to the physical stability analysis, HIU pretreatment, especially at 450 W power, significantly improved the physical stability of MP emulsions, as evidenced by the reduced particle size, enhanced inter-droplet interactions, and increased uniformity of the droplet size distribution (p < 0.05). The results of interfacial protein composition, Fourier transform infrared spectroscopy analysis, and microscopic morphology observation of the aqueous MP suspension suggested that HIU induced the depolymerization of filamentous myosin polymers and inhibited the subsequent self-assembly behavior. These effects may facilitate protein adsorption and molecular rearrangement at the oil–water interface, forming a complete interfacial layer and, thus, droplet stabilization. Confocal laser scanning microscopy observations further confirmed these results. In conclusion, these findings provide direct evidence for the role of HIU in improving the physical stability of MP emulsions at low ionic strength.
Effects of different freeze–thaw cycles (0, 1, 3 and 5) on physicochemical change and protein oxidation in porcine longissimus dorsi were investigated. When the number of freeze–thaw cycles ...increased, the thawing losses, cooking loss and
b*-value increased (
P
<
0.05),
a*-value decreased (
P
<
0.05). The cutting forces of pork increased after one cycle of freeze–thaw (from 28.3
N to 40.4
N) (
P
<
0.05), but the further increase of freeze–thaw cycles would lead to decrease of cutting force. The decreases in Ca
2+- and K
+-ATPase activity and sulfhydryl group (
P
<
0.05) content with concomitant increases in carbonyl content and thiobarbituric acid-reactive substances (TBARS) value (
P
<
0.05) showed that multiple freeze–thaw could cause the porcine protein and fat oxidation, especially for the pork subjected to five freeze–thaw cycles. Gel electrophoresis patterns of porcine muscle showed that multiple freeze–thaw cycles could cause cross-linking of protein in myofibril. Overall, the freeze–thaw process has a detrimental effect on the quality of pork.
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•Porcine plasma protein hydrolysates interacted with oxidized phenolic compounds.•The interaction occurred via covalent, disulphide, and hydrogen bonds.•Modified porcine plasma ...protein hydrolysates had higher antioxidant activities.•Modified porcine plasma protein hydrolysates had higher emulsifying stability.•It also had decreased emulsifying activity due to lower surface hydrophobicity.
Physicochemical characteristics, antioxidant activities and emulsifying properties of porcine plasma protein hydrolysates (PPPH) modified with oxidized tannic acid (OTA) or oxidized chlorogenic acid (OCA) were investigated. The formation of complexes was showed by increased turbidity, and both OTA and OCA were covalently attached to PPPH as shown by the significantly decrease in free amino group contents (P < 0.05). Fourier transform infrared spectroscopy also indicated cross-linking between PPPH and OTA or OCA through hydrogen bonds. More importantly, compared with PPPH alone, modification of OTA or OCA endowed PPPH with a higher emulsifying stability index and greater antioxidant activities. However, the emulsifying activity index of PPPH significantly decreased after modification (P < 0.05), which is associated with lower surface hydrophobicity. These results suggest that PPPH-OTA and PPPH-OCA complexes could be used as efficient antioxidants and potential emulsifiers in emulsion-food systems.
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•High-intensity ultrasound and pH-shifting improve pea protein solubility.•The combined treatment reduced the particle size of pea protein.•The combined treatment exposed hydrophobic ...residues of pea protein.•High-intensity ultrasound and pH-shifting promote the emulsion physical stability.
The most important factors restricting research and application in the food industry are the poor solubility and emulsification of pea protein isolate (PPI). This study investigates the effect of high-intensity ultrasound (HIU, 0–600 W) and pH-shifting treatment, alone or combined, on the structure, solubility, and emulsification of PPI, as well as its potential mechanism. The results revealed that the PPI solubility significantly increases when treated with the combination, corresponding to a decrease in the protein particle size, especially at 500 W of HIU power (p < 0.05). Correspondingly, the emulsion prepared from it was less prone to phase separation during storage. According to the structural analysis, the structural changes caused by protein unfolding (i.e., the exposure of hydrophobic and polar sites and the loss of the α-helix) seemed to be the primary reasons for increased PPI solubility. In addition, confocal laser scanning microscopy indicated that the combination treatment accelerated the adsorption of PPI at the oil/water interface and strengthened the compactness of the interface film. Improved interfacial properties and intermolecular forces played a critical role in the resistance to droplet coalescence in PPI emulsion. In conclusion, ultrasound and pH-shifting treatments have a synergistic effect on improving the solubility and emulsification of PPI.
The effect of partial replacement of NaCl by using sodium substitutes (SS) on the physical, microbial and sensory characteristics of Harbin dry sausage was investigated. There were three salt ...formulations, including control (100% NaCl), NaCl partly substituted by KCl (SS1) (70% NaCl and 30% KCl), and NaCl partly substituted by KCl combined with other components (SS2) (70% NaCl, 20% KCl, 3.5% maltodextrin, 4% L-Lys, 1% L-Ala, 0.5% citric acid and 1% Ca-lactate). After a 12-day fermentation, the higher moisture content and Aw and lower pH were found in the SS2 treatment, compared to the control and SS1 treatments (P < .05). A decreased microbial diversity during fermentation was found in all sausages, and Staphylococcus spp. and Lactobacillus spp. became the dominant genera. Additionally, the SS2 treatment showed a higher L*-value and lower hardness and chewiness values (P < .05). Therefore, the formulation of SS2 could achieve a NaCl reduction of 30% in Harbin dry sausages with a better sensory acceptability.
•Sausages with sodium substitutes had higher moisture content and water activity.•Lactobacillus and Staphylococcus became the dominant bacteria in the sausages.•Sodium substitute SS2 could replace 30% NaCl in Harbin dry sausage.
The inhibiting effect of ice structuring protein (ISP) with different additions on the quality deterioration and oxidation of mirror carp induced by freeze-thaw (F-T) cycles was investigated. It can ...be concluded that the whiteness, water holding capacity, cutting force and thermal stability of the sample without ISP were significantly decreased, and oxidation reactions were aggravated with the increasing in F-T cycles (P < 0.05). The centrifugal loss, thawing loss and cooking loss of 2.0 (g/L) ISP samples were decreased by 43.3%, 57.3% and 27.6% than the sample without ISP. In addition, ISP could effectively restrain moisture migration and destruction of microstructure of mirror carp during F-T cycles. More importantly, inhibitory effect of 2.0 ISP on oxidation was verified from the decrease in carbonyl contents (16.7%) and TBARS value (21.5%) of mirror carp compared with control.
•F-T cycles accelerated quality deterioration and oxidation of mirror carp.•ISP (ice structuring protein) inhibited the F-T damage of mirror carp quality.•Inhibiting effect of 2.0 (g/kg) ISP on quality decline of mirror carp was obvious.•ISP retarded the losses on microstructure of mirror carp during F-T cycles.
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•LAB, except for L. curvatus R5, from dry sausage tolerated the human GI tract.•Different cell components of LAB have different modes of antioxidant action.•LAB from dry sausage had ...similar probiotic property to that of selected probiotics.•LAB isolated from Harbin dry sausages can be used as potential probiotics.
The probiotic properties of lactic acid bacteria (LAB) Pediococcus pentosaceus R1, Lactobacillus brevis R4, Lactobacillus curvatus R5, and Lactobacillus fermentum R6 isolated from Harbin dry sausages were evaluated and compared in vitro with those of selected probiotics from fermented dairy products, including Lactobacillus acidophilus, Lactobacillus plantarum, L. curvatus, Lactobacillus sake, Lactobacillus pentosaceus, and L. fermentum. These four strains tolerated the human gastrointestinal (GI) tract well, except for L. curvatus R5. The auto-aggregation percentages and adhesion rates of LAB varied greatly; L. brevis R4 showed the greatest aggregation and adhesion. The antioxidant action of LAB varied with the cell components. Intracellular cell-free extracts of the LAB showed better inhibition of lipid peroxidation, whereas intact cells and cell-free supernatants showed better ABTS+ scavenging ability and reducing power, respectively. Results revealed that these LAB isolated from Harbin dry sausages have strong probiotic properties and can be used as potential probiotics for food processing.
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