Changwei Ma

Antioxidant properties of peptide fractions from silver carp (Hypophthalmichthys molitrix) processing by-product protein hydrolysates evaluated by electron spin resonance spectrometry.

Silver carp processing by-product protein is usually discarded as an industrial solid waste. In this study the protein was recovered using a pH-shift method, after which seven commercial proteases were separately employed to prepare antioxidative hydrolysates. Among the hydrolysates, pepsin hydrolysates, which had the highest free radical-scavenging activity, were further separated into five peptide fractions, SCPH-I (>10kDa), SCPH-II (5-10kDa), SCPH-III (3-5kDa), SCPH-IV (1-3kDa), and SCPH-V (<1kDa), by using ultrafiltration. The antioxidative properties of the peptide fractions were investigated, using a free radical-scavenging assay, by electron spin resonance. The results show that SCPH-V had the highest scavenging effects on DPPH (1,1-diphenyl-2-picrylhydrazyl), hydroxyl and superoxide anion radicals. SCPH-V had potent antioxidant activity in the prevention of the peroxidation of linoleic acid and alleviation of H2O2-induced oxidative stress in human intestinal epithelial caco-2 cells. The results indicated that the antioxidant capacity of silver carp by-product hydrolysates could be enhanced by ultrafiltration.

Lipolysis in intramuscular lipids during processing of traditional Xuanwei ham

Lipolysis in intramuscular lipids during the processing of Chinese Xuanwei ham has been studied by analyzing the changes of glycerides, phospholipids and free fatty acids in biceps femoris muscle. Results showed that the glycerides accounted for 73.2% of total lipid content in fresh ham, the phospholipids represented 25.3% and the free fatty acids 2.3% of the total lipid content, respectively. A rapid lipolysis of phospholipids occurred during the first 4 months of processing and slowed down during the rest period. A preferential hydrolysis for palmitic, linoleic and arachidonic acids in phospholipid fraction was observed. Glycerides only changed a little throughout the process, while an increase of free fatty acids during processing was observed. The results suggest that phospholipids are the main substrate of lipolysis in the intramuscular lipids of Chinese Xuanwei ham.

Physico-chemical characteristics and free fatty acid composition of dry fermented mutton sausages as affected by the use of various combinations of starter cultures and spices

The microbiological, physico-chemical and free fatty acid composition of dry fermented mutton sausages were determined during ripening and storage. Three sausage mixtures (starter culture [SC], SC and black pepper [SC+BP] and SC, BP and cumin [SC+BP+C]) were compared with a control (CO). In general, the lactic acid bacteria populations in the SC+BP increased significantly to 9 log CFU/g and were higher than the CO (8 log CFU/g) (P<0.05) from fermentation to ripening. The pH values of the SC, SC+BP and SC+BP+C were 4.81, 4.55 and 4.53 respectively, significantly lower (P<0.05) than the CO at the end of fermentation. The water activity (a(w)) in all sausages decreased significantly to 0.88 at Day 7. The total free fatty acid (TFFA) in the treatments increased significantly (P<0.05) during ripening and storage. The levels of MUFA+PUFA/SFA in SC+BP and SC+BP+C at Day 7 were 2.44 and 2.31 respectively, higher than the control (1.65) (P>0.05).

Effects of diet, packaging, and irradiation on protein oxidation, lipid oxidation, and color of raw broiler thigh meat during refrigerated storage

This study was designed to evaluate the effects of dietary treatment, packaging, and irradiation singly or in combination on the oxidative stability of broiler chicken thigh meat. A total of 120 four-week-old chickens were divided into 12 pens (10 birds/pen), and 4 pens of broilers were randomly assigned to a control oxidized diet (5% oxidized oil) or an antioxidant-added diet [500 IU of vitamin E + 200 mg/kg of butylated hydroxyanisole (BHA)] and fed for 2 wk. After slaughter, thigh meats were separated, ground, packaged in either oxygen-permeable or oxygen-impermeable vacuum bags, and irradiated at 0 or 3 kGy. Lipid oxidation (TBA-reactive substances), protein oxidation (carbonyl), and color of the meat were measured at 1, 4, and 7 d of refrigerated storage. The lipid and protein oxidation of thigh meats from birds fed the diet supplemented with antioxidants (vitamin E + BHA) was significantly lower than the lipid and protein oxidation of birds fed the control diet, whereas the lipid and protein oxidation of broilers fed the oxidized oil diet was higher than that of birds fed the control diet. Vacuum packaging slowed, but irradiation accelerated, the lipid and protein oxidation of thigh meat during storage. Dietary antioxidants (vitamin E + BHA) and irradiation treatments showed a stronger effect on lipid oxidation than on protein oxidation. A significant correlation between lipid and protein oxidation in meat was found during storage. Dietary supplementation of vitamin E + BHA and the irradiation treatment increased the lightness and redness of thigh meat, respectively. It is suggested that appropriate use of dietary antioxidants in combination with packaging could be effective in minimizing oxidative changes in irradiated raw chicken thigh meat.

Isolation of cathepsin B from the muscle of silver carp (Hypophthalmichthys molitrix) and comparison of cathepsins B and L actions on surimi gel softening.

Cathepsin B from silver carp muscle was purified to 263-fold by acid treatment, ammonium sulfate fractionation, followed by a series of chromatographic separations. The molecular mass of the purified enzyme was 29kDa as determined by SDS-PAGE and immunoblotting. The purified enzyme was activated by dithiothreitol and cysteine while it was substantially inhibited by E-64, suggesting the purified enzyme belongs to the cysteine proteinase family. Optimal pH and temperature were 5.5 and 35°C, respectively. The enzyme catalyzed the hydrolysis of Z-Arg-Arg-MCA with a parameter of Km (90μM) and Kcat (20.3s(-1)), but hardly hydrolyzed Arg-MCA. Analysis of surimi gel strength and microstructure showed that cathepsins B and L were capable of destroying the network structure of silver carp surimi gels, consequently causing gel softening. Cathepsin L might play an important role in the modori effect.

Lipids deposition, composition and oxidative stability of subcutaneous adipose tissue and Longissimus dorsi muscle in Guizhou mini-pig at different developmental stages

The aim of this study was to investigate the effect of developmental stage on lipids deposition, composition and oxidative stability of subcutaneous adipose tissue (SAT) and Longissimus dorsi muscle (LDM) in Guizhou mini-pig. Pigs were raised in the same condition, and SAT and LDM were sampled on 90 d, 180 d and 270d. Lipids content decreased (P<0.01) from 90 d to 180 d and increased (P<0.01) from 180 d to 270 d in SAT and LDM. Neutral lipids in both tissues decreased (P<0.01) from 90 d to 180 d and increased (P<0.01) from 180 d to 270 d, while phospholipids content changed inversely during the three selected time points. Developmental times had great influence on fatty acids (FAs) composition of neutral lipids, phospholipids and free fatty acids (FFAs) except FAs composition of FFAs in SAT. Lipids oxidative stability in SAT and LDM both decreased between 90 d and 180 d (P<0.05) and increased by 270 d (P<0.05). In conclusion, due to the increased contents of unsaturated fatty acids and decreased oxidation stability, Guizhou or other mini-pigs slaughtered at an early age may have a negative effect on meat quality.