Xiufang Xia

Physicochemical change and protein oxidation in porcine longissimus dorsi as influenced by different freeze-thaw cycles.

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 28.3N to 40.4N) (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.

Antioxidant activity of black currant (Ribes nigrum L.) extract and its inhibitory effect on lipid and protein oxidation of pork patties during chilled storage

This experiment was conducted to assess the antioxidant efficacy of black currant (Ribes nigrum L.) extract (BCE) in raw pork patties during chilled storage. The extracting conditions of frozen BCE including ethanol concentrations (0-100%) and extracting times (0.25-12h) were studied. BCE extracted with 40% ethanol for 2h had the highest anthocyanin content, the strongest radical scavenging activities as well as the second strongest reducing power. BCE was condensed and added to pork patties at 5, 10 or 20 g/kg. Compared with the control, BCE treatments significantly decreased the thiobarbituric acid-reactive substance values and carbonyls formation and reduced the sulfhydryl loss of pork patties in a dose-dependent manner (P<0.05), which showed that the BCE significantly inhibited lipid and protein oxidation. The BCE-treated patties showed significantly higher redness (P<0.05) than the control. The findings demonstrated strong potential for BCE as a natural antioxidant in meat and meat products.

Decreased gelling and emulsifying properties of myofibrillar protein from repeatedly frozen-thawed porcine longissimus muscle are due to protein denaturation and susceptibility to aggregation

The effects of freeze-thaw cycles (FT, 0, 1, 3 and 5 times) on protein functional properties of porcine longissimus muscle were investigated. FT increased gapping between muscle fibres and tore muscle fiber bundles. Myofibrillar protein (MP) isolated from FT muscle showed an increased hydrophobicity (P<0.05), reduced thermal transition temperatures (T(max)) and enthalpy of denaturation (DeltaH) (P<0.05), and enhanced susceptibility to thermal aggregation. These structural changes resulted in major losses in protein functionalities, e.g., 41-43% reductions (P<0.05) in MP emulsifying capacity and emulsion stability after five FT cycles. The ability of MP to form a viscoelastic gel network, as analyzed by small-strain oscillatory rheological testing, also attenuated with FT cycles. The FT process lowered (P<0.05) water-holding capacity (WHC), whiteness, and texture (hardness, springiness, chewiness and cohesiveness) of MP gels. Overall, repeated FT had a detrimental effect on the general functionality of porcine MP, and protein denaturation and aggregation were implicated in the functionality losses.

Hepatoprotective and antioxidant effects of porcine plasma protein hydrolysates on carbon tetrachloride-induced liver damage in rats

Porcine plasma protein hydrolysate (PPH) prepared by alcalase for 5 h was fractioned by ultrafiltration. Four fractions, H(1) (MW>10k), H(2) (MW 6-10k), H(3) (MW 3-6k) and H(4) (MW<3k), were obtained. H(4) possessed the highest antioxidant activity as indicated by thiobarbituric acid-reactive substance values and hydroxyl radical scavenging activity (P<0.01). Male rats were pretreated with H(4) at dose of 50, 100, and 200 mg/kg of body weight orally once daily for 12 days, then they were treated intraperitoneally with a single dose of CCl(4) (2 mL/kg of body weight). The results showed that oral feeding of H(4) could significantly lower (P<0.01) the serum levels of hepatic enzyme markers (aspartate transaminase and alanine transaminase). Compared with the CCl(4)-only treatment group, levels of hepatic superoxide dismutase, glutathione peroxidase, catalase and total antioxidant capacity were significantly increased, and the malondialdehyde levels were sharply decreased (P<0.01) in rats treated by all doses of PPH fraction H(4). A histological examination of the liver showed that lesions, including necrosis, lymphocyte infiltration and fatty degeneration, were partially healed by treatment with H(4) fractions. These data suggest that in rats, PPH can protect the liver against CCl(4)-induced oxidative damage.

Moisture migration, microstructure damage and protein structure changes in porcine longissimus muscle as influenced by multiple freeze-thaw cycles

This study investigated the effects of multiple freeze-thaw (F-T) cycles on water mobility, microstructure damage and protein structure changes in porcine longissimus muscle. The transverse relaxation time T2 increased significantly when muscles were subjected to multiple F-T cycles (P<0.05), which means that immobile water shifted to free water and the free water mobility increased. Multiple F-T cycles caused sarcomere shortening, Z line fractures, and I band weakening and also led to microstructural destruction of muscle tissue. The decreased free amino group content and increased dityrosine in myofibrillar protein (MP) revealed that multiple F-T cycles caused protein cross-linking and oxidation. In addition, the results of size exclusion chromatography, circular dichroism spectra, UV absorption spectra, and intrinsic fluorescence spectroscopy indirectly proved that multiple F-T cycles could cause protein aggregation and degradation, α-helix structure disruption, hydrophobic domain exposure, and conformational changes of MP. Overall, repeated F-T cycles changed the protein structure and water distribution within meat.

Cryoprotectants Reduce Protein Oxidation and Structure Deterioration Induced by Freeze-Thaw Cycles in Common Carp (Cyprinus carpio) Surimi

The objective of the present study was to investigate the effects of a cryoprotectant (a mixture of sucrose and sorbitol) on protein and lipid oxidation and structural changes in common carp (Cyprinus carpio) surimi subjected to different numbers of freeze-thaw (FT) cycles. Increased numbers of FT cycles were accompanied by increases in carbonyl content and thiobarbituric acid-reactive substances values and concomitant decreases in sulphydryl group (P<0.05) content, revealing that multiple FT cycles could cause protein and lipid oxidation in the carp tissue. Myofibrillar protein isolated from FT surimi also showed a reduced ATPase activity (P<0.05), increased hydrophobicity (P<0.05), and enhanced susceptibility to thermal aggregation. The addition of cryoprotectants significantly inhibited carbonyl formation and lipid oxidation (P<0.05), and its good protective effect on protein denaturation was demonstrated by its efficacy in maintaining Ca-ATPase activity, reducing the rapid exposure of hydrophobic and sulphydryl groups on the protein surface, and decreasing the degree of protein aggregation. Overall, the use of cryoprotectants reduced protein oxidation and structural deterioration induced by freeze-thaw in common carp surimi.

Changes in Physicochemical and Protein Structural Properties of Common Carp (Cyprinus carpio) Muscle Subjected to Different Freeze–Thaw Cycles

The present study investigated physicochemical and protein structural changes in common carp muscle subjected to different freeze–thaw (FT) cycles. With increasing number of FT cycles, the thawing losses, cooking loss, L*- and b*-value increased, and shear forces and a*-value decreased (p < 0.05). The study showed that multiple FT processes were detrimental to color and water-holding capacity of carp muscle. The increases in thiobarbituric acid reactive substances and carbonyl content with concomitant decrease in sulfhydryl group content (p < 0.05) showed that multiple FT caused carp lipid and protein oxidation, especially for the carp muscle subjected to five freeze–thaw cycles. Myofibrillar protein isolated from FT muscle showed an increased hydrophobicity, reduced ATPase activity, and enhanced susceptibility to thermal aggregation (p < 0.05). These protein structural changes resulted in major losses in muscle quality. Overall, the disrupted protein structure, together with the denaturation of myofibrillar protein induced by FT, was most likely associated with lowered muscle quality.

Thermal stability and gel quality of myofibrillar protein as affected by soy protein isolates subjected to an acidic pH and mild heating

Thermal stability and gel quality of myofibrillar protein were evaluated with regard to the addition of native soy protein isolates (SPI) and SPI subjected to acidic pH and mild heating (modified SPI). Compared with the control, the addition of modified SPI increased the compression force of the protein gel and decreased water loss (P<0.05). Differential scanning calorimetry results showed that an addition of 0.75% native SPI decreased the first transition temperature (P<0.05), and addition of 0.5% and 0.75% modified SPI exhibited no appreciable changes on it (P>0.05), indicating that a higher concentration of modified SPI would not damage the protein thermal stability. Moreover, the addition of modified SPI enhanced hydrogen bonding and disulphide linkages. Atomic force microscopy analysis revealed that the addition of modified SPI decreased the roughness of the mixed myofibrillar protein gels. Overall, modified SPI has the potential to improve myofibrillar protein gel texture and water holding capacity.

Effect of porcine plasma protein hydrolysates on long-term retrogradation of corn starch

The potential effect of porcine plasma protein hydrolysates (PPPH) on the long-term retrogradation of corn starch (CS) was investigated. The differential scanning calorimetry results showed that PPPH significantly reduced the retrogradation enthalpies (ΔHr) of CS (P<0.05), obviously decreased the crystallization rate constant (k), and enhanced the Avrami exponent (n) (P<0.05). Low-field nuclear magnetic resonance analysis demonstrated that the spin-spin relaxation time (T2) remarkably increased with increasing PPPH concentration during storage at 4°C for 28days (P<0.05). The X-ray diffraction results revealed that the relative crystallinity of retrograded CS decreased from 13.04% to 8.73% with the addition of PPPH. Fourier transform infrared spectroscopy analysis demonstrated that the addition of PPPH led to a decrease in hydrogen bonds within starch. The results demonstrated that the addition of PPPH apparently played a crucial role in retarding the long-term retrogradation of CS.

Influence of ultrasound-assisted immersion freezing on the freezing rate and quality of porcine longissimus muscles

The objective of this study was to evaluate the effect of ultrasound-assisted immersion freezing (UIF) on the freezing rate and quality of porcine longissimus muscles under different ultrasound powers. UIF with a certain level of ultrasound power significantly (P>0.05) accelerated the freezing rate. The phase transition times of samples treated with UIF at 180W (UIF-180) were the shortest. There were no significant differences (P>0.05) in a* (redness), b* (yellowness), pH values or cooking loss among UIF, IF, and control (fresh muscle) samples. Investigation of the microstructure of frozen muscles demonstrated that UIF-180 remarkably reduced the size of ice crystals and made their distribution more uniform. UIF-180 samples showed a significant (P<0.05) reduction in thawing loss and T21 and T22 relaxation times compared with other treatments, which meant that UIF at certain powers could reduce the mobility and loss of immobilized and free water. The results showed that UIF at certain powers significantly increased the freezing rate of muscle samples and improved meat quality.