Shan Xiao

Improving functional value of meat products

In recent years, much attention has been paid to develop meat and meat products with physiological functions to promote health conditions and prevent the risk of diseases. This review focuses on strategies to improve the functional value of meat and meat products. Value improvement can be realized by adding functional compounds including conjugated linoneleic acid, vitamin E, n3 fatty acids and selenium in animal diets to improve animal production, carcass composition and fresh meat quality. In addition, functional ingredients such as vegetable proteins, dietary fibers, herbs and spices, and lactic acid bacteria can be directly incorporated into meat products during processing to improve their functional value for consumers. Functional compounds, especially peptides, can also be generated from meat and meat products during processing such as fermentation, curing and aging, and enzymatic hydrolysis. This review further discusses the current status, consumer acceptance, and market for functional foods from the global viewpoints. Future prospects for functional meat and meat products are also discussed.

Protein Oxidation: Basic Principles and Implications for Meat Quality

The involvement of oxidized proteins to the development of biological diseases has been studied for a few decades, but the effects and the mechanisms of protein oxidation in food systems are largely unknown. Protein oxidation is defined as the covalent modification of a protein induced either by the direct reactions with reactive oxygen species (ROS) or indirect reactions with secondary by-products of oxidative stress. ROS can cause oxidation in both amino acid side chains and protein backbones, resulting in protein fragmentation or protein–protein cross-linkages. Although all amino acids can be modified by ROS, cysteine, and methionine that are the most susceptible to oxidative changes due to high reaction susceptibility of the sulfur group in those amino acids. Oxidative modifications of proteins can change their physical and chemical properties, including conformation, structure, solubility, susceptibility to proteolysis, and enzyme activities. These modifications can be involved in the regulation of fresh meat quality and influence the processing properties of meat products. Oxidative stress occurs when the formation of oxidants exceeds the ability of antioxidant systems to remove the ROS in organisms. Increased levels of protein oxidation have been associated with various biological consequences, including diseases and aging, in humans and other animal species. The basic principles and products of protein oxidation and the implications of protein oxidation in food systems, especially in meat, are discussed in this review.

Consumption of Oxidized Oil Increases Oxidative Stress in Broilers and Affects the Quality of Breast Meat

A total of 120 4-week-old broiler chickens were allotted to 12 pens and fed one of three diets including control, oxidized diet (5% oxidized oil), or antioxidant-added diet (500 IU vitamin E) for 2 weeks. Blood samples were collected at the end of feeding trial, and breast muscles were sampled immediately after slaughter. Breast meats were also collected 24 h after slaughter and used for meat quality measurements. Oxidative stress in blood, lipid and protein oxidation, and sarcoplasmic reticulum Ca²(+)-ATPase (SERCA) activity of breast muscle were determined. The oxidized diet increased oxidative stress in blood and increased carbonyl content in breast meat compared with the other two dietary treatments (P < 0.05). Lipid oxidation of breast muscles with the antioxidant-supplemented diet was lower than that with the oxidized and control diet groups (P < 0.05). Meat from birds fed the oxidized diet showed higher drip loss after 1 and 3 days of storage and greater 0-1 h post-mortem pH decline (P < 0.05). Significant differences in specific SERCA activity in breast muscles from birds fed control and oxidized diets (P < 0.05) were detected. This suggested that dietary oxidized oil induced oxidative stress in live birds and increased lipid and protein oxidation in breast muscle. Decrease in SERCA activity in breast muscles due to oxidative stress in live animals accelerated post-mortem glycolysis, which sped the pH drop after slaughter and increased drip loss, indicating that oxidation of diet can cause PSE-like (pale, soft, and exudative) conditions in broiler breast muscles.

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.

Lipid and protein oxidation of chicken breast rolls as affected by dietary oxidation levels and packaging.

The objective of this study was to determine the effects of dietary treatment and packaging on the oxidative stability of breast rolls. A total of 120 4-wk-old broiler chickens were randomly assigned to control, oxidized diet (5% oxidized oil, PV = 100), or antioxidants-added diet (500 IU vitamin E + 200 ppm BHA) and fed for 2 wk. Breast muscles were separated from the carcasses and breast rolls were prepared. The rolls were cooked in a smoke house (85 °C) to an internal temperature of 74 °C, cooled, sliced to 2-cm thick pieces, individually packaged in oxygen permeable bags or vacuum-packaged in oxygen impermeable bags, and stored in a 4 °C cold room for 7 d. Lipid, protein oxidation and volatiles were determined at 1, 4, and 7 d of storage. Dietary supplementation of antioxidants significantly reduced lipid oxidation (TBARS) and protein oxidation (carbonyls) in breast rolls, and the effect of dietary antioxidants on lipid oxidation was more pronounced than protein oxidation. Chicken breast rolls from antioxidants treatment group produced significantly lower amounts of hexanal and pentanal than those from control and oxidized oil treatments (P < 0.05). However, dietary oxidized oil did not increase lipid and protein oxidation in breast rolls. Vacuum-packaging significantly delayed the onset of lipid oxidation and protein oxidation in chicken rolls during 7-day refrigerated storage (P < 0.05). Therefore, it is suggested that appropriate use of dietary supplementation of antioxidants in combination with packaging could minimize lipid oxidation in chicken breast rolls.

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.