Jianhao Zhang

Crude lipoxygenase from pig muscle: partial characterization and interactions of temperature, NaCl and pH on its activity.

Crude lipoxygenase (LOX) was extracted from fresh pig bacon belly and studied of partial characteristics. The interactions of temperature, sodium chloride (NaCl) and pH on LOX activity were investigated by response surface methodology (RSM). Kinetic studies indicated that the Michaelis constant (K(m)) and maximum velocity (V(max)) for LOX activity using linoleic acid as substrate were 68 μM and 0.26 U/min at 20°C, respectively. The optimal conditions for this reaction were: substrate concentration 3.47 mM, reaction temperature 39°C and pH ≧9.0. The NaCl critical value for LOX activity was 3.0% (w/w) at 20°C, above which the LOX activity began to decrease. Temperature had significant interactions (p<0.05) with NaCl and pH. The temperature critical value decreased with NaCl content increasing, while increased with pH increasing. These indicated that LOX activity and enzyme-catalyzed lipid oxidation in dry-cured meat products could be regulated by controlling process factors during the processing.

Influence of partial replacement of NaCl with KCl on profiles of volatile compounds in dry-cured bacon during processing

This study investigated the influence of partial substitution of NaCl with KCl on the formation of volatile compounds in bacons during processing using a purge and trap dynamic headspace GC/MS system. Three substitutions were 0% KCl (I), 40% KCl (II), and 70% KCl (III). The profiles of the volatile compounds significantly changed during processing, particularly during the drying/ripening. At the end of process, the bacons from substitution III formed significantly higher levels of lipid-derived volatiles, such as straight chain aldehydes, hydrocarbons than bacons from substitution I and II, whereas the latter formed higher levels of volatiles from amino acid degradation such as 3-methylbutanal. There were very few differences in volatile formation between 0% and 40% KCl application. These results suggest that K(+) substitution of Na(+) by more than 40% may significantly change profiles of volatiles in finished dry-cured bacons and therefore would result in changes in the product aroma and/or flavour.

Proteolysis and sensory properties of dry-cured bacon as affected by the partial substitution of sodium chloride with potassium chloride

Quadriceps femoris muscle samples (48) from 24 pigs were processed into dry-cured bacon. This study investigated the influence of partial substitution of sodium chloride (NaCl) with potassium chloride (KCl) on proteolysis and sensory properties of dry-cured bacon. Three salt treatments were considered, namely, I (100% NaCl), II (60% NaCl, 40% KCl), and III (30% NaCl, 70% KCl). No significant differences were observed among treatments in the proteolysis, which was reflected by SDS-PAGE, proteolysis index, amino acid nitrogen, and peptide nitrogen contents. Furthermore, there were no significant differences in the moisture content between control and treatment II, whereas the moisture content in treatment III was significantly higher (p<0.05) in comparison with control (treatment I). The sensory analysis indicated that it was possible to reduce NaCl by 40% without adverse effects on sensory properties, but 70% replacement of NaCl with KCl resulted in bacon with less hardness and saltiness and higher (p<0.05) juiciness and bitterness.

Shell thickness-dependent antibacterial activity and biocompatibility of gold@silver core–shell nanoparticles

Antimicrobial activity of silver is highly effective and broad-spectrum; however, poor long-term antibacterial efficiency and cytotoxicity toward mammalian cells have restricted their applications. Here, we fabricated Au@Ag NPs with tailored shell thickness, and investigated their antibacterial activities against both Gram-negative bacteria (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus) and the cytotoxicity toward SH-SY5Y human cells, for the first time. Our results demonstrate that Au@Ag NPs with a thickness of 5 nm or Au : Ag ratio 1 : 1 (Au@Ag-2 NPs) have the highest antibacterial activity and excellent biocompatibility. The minimum inhibitory concentration (MIC) values of Au@Ag-2 NPs in terms of effective silver concentration are 5 µg mL−1 for E. coli and 7.5 µg mL−1 for S. aureus, which is significant lower than that of Ag NPs or the simple mixture of Ag and Au NPs and suggests the synergistic effects of Au and Ag in core–shell NPs. Live/dead bacterial assay and scanning electron microscope (SEM) images demonstrated that the Au@Ag NPs disrupt the bacterial cell membrane which subsequently results in cellular material leakage and cell death. The Au@Ag NPs may have great potential as effective antibacterial agents for pathogen control in hospitals and food processing.

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.

Effect of Monascus as a nitrite substitute on color, lipid oxidation, and proteolysis of fermented meat mince

Monascus spp. are fungi, traditionally eaten in Asian countries, that have the the potential to be used as a nitrite substitute in meat-product processing. Effects of using Monascus ruber MJ-1 as a nitrite substitute on color, lipid oxidation and proteolysis of fermented meat mince were investigated in this study. After 4 days of fermentation, a* and L* values for the samples were significantly higher and lower than the values for the control, respectively; however, b* values were significantly lower than that of the control throughout the fermentation process (p<0.05). Furthermore, Monascus ruber MJ-1 fermentation decreased the thiobarbituric acid reactive substances (TBARs) value and increased the myofibril fragmentation index (MFI) value of meat mince significantly (p<0.05). SDS-PAGE results further indicated that myofibrillar proteins were degraded during fermentation, while sarcoplasmic proteins were not. These results suggest prospects for the broad application of Monascus as a nitrite substitute in meat processing.

DNA-engineered chiroplasmonic heteropyramids for ultrasensitive detection of mercury ion.

In this study, plasmonic heteropyramids (HPs) made from two different sized gold nanoparticles (Au NPs) and five ssDNA sequences and their application for ultrasensitive detection of mercury ion (Hg(2+)) were demonstrated. Four ssDNA sequences were used as building blocks to form a pyramidal DNA frame, which contains a T-rich probe DNA at one vertex and three sulfhydryl groups modified with 10nm Au NPs at the other three vertices. Another T-rich DNA sequence was modified and attached to a 25 nm Au NP. In the presence of Hg(2+) ions, 25 nm Au NPs hybridized with pyramidal DNA frame to build the plasmonic HPs based on T-Hg(2+)-T interaction, which exhibits unprecedented circular dichroism (CD) signal in the visible region. Based on this mechanism, a simple, high sensitive and selective chiroplasmonic HPs-based probe was constructed and demonstrated for Hg(2+) ions detection. Under optimized conditions, Hg(2+) ions could be selectively detected in a concentration range from 1 to 500 pg mL(-1) with a limit of detection of 0.2 pg mL(-1), which is much lower than the strictest Hg(2+) safety requirement of 1 ng mL(-1) in water.

Antioxidant activities of ginger extract and its constituents toward lipids

Lipid oxidation-a major cause of food product deterioration-necessitates the use of food additives to inhibit food oxidation. Ginger extract (GE) has been reported to possess antioxidant properties. However, components isolated from ginger have been rarely reported to inhibit fat oxidation. Herein, antioxidant properties of GE and four pure components derived from it (6-gingerol, 8-gingerol, 10-gingerol, and 6-shogaol) were examined and their properties were compared to those of butylated hydroxytoluene. GE and the constituent components exhibited antioxidant properties that might be attributed to their hydroxyl groups and suitable solubilizing side chains. 6-Shogaol and 10-gingerol exhibited higher activity at 60°C than 6-gingerol and 8-gingerol. Low antioxidant activity was detected at high temperatures (120/180°C). Overall, GE displayed the strongest dose-dependent antioxidant properties, especially at high temperatures, thereby demonstrating that GE can be employed as a natural antioxidant in lipid-containing processed foods.

Influence of partial replacement of NaCl with KCl on formation of volatile compounds in Jinhua ham during processing

The influence of partial replacement of NaCl with KCl on formation of volatile compounds during Jinhua ham processing was evaluated using GC/MS system. Jinhua ham was treated with either 100% NaCl (I) or 60% NaCl and 40% KCl (II). Formation of volatile compounds increased in Jinhua hams during processing for both salt formulations, particularly at the end of the salting period. There were differences in volatile compound formation between formulations I and II after 45 days of processing. Contents of lipid-derived volatiles (hexanal) and Strecker aldehydes (2-methylbutanal and 3-methylbutanal) were higher in Jinhua hams treated with formulation II after 45 days of processing. Partial salt replacement of NaCl with KCl changed formation of volatile compounds in Jinhua hams and may have affected the flavor of finished products.

Oxidative stability and antioxidant enzyme activities of dry-cured bacons as affected by the partial substitution of NaCl with KCl.

This study investigated the influence of partial substitution of NaCl with KCl on protein and lipid oxidation as well as antioxidant enzyme activities in dry-cured bacons during processing. The partial substitution was 0% KCl (I), 40% KCl (II), and 70% KCl (III). Compared with 0% KCl (I), the substitution of 40% NaCl with KCl did not significantly influence the protein and lipid oxidation and antioxidant enzyme activities. The bacons that were treated with 70% KCl treatment (III) showed increased lipid oxidation and antioxidant enzyme GSH-Px activity, whereas samples treated with formulas I and II showed higher protein oxidation and antioxidant enzyme catalase activity. These results demonstrate that the substitution of NaCl with KCl by more than 40% may significantly affect protein and lipid oxidation and that for the substitution of NaCl in further processed meat products with other chloride salts, salt content is very important for control of protein and lipid biochemical changes in finished products.