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.

The effect of heat treatment on the antioxidant activity of extracts from Citrus unshiu peels was evaluated. Citrus peels (CP) (5 g) were placed in Pyrex Petri dishes (8.0 cm diameter) and heat-treated at 50, 100, or 150 degrees C for 10, 20, 30, 40, 50, and 60 min in an electric muffle furnace. After heat treatment, 70% ethanol extract (EE) and water extract (WE) (0.1 g/10 mL) of CP were prepared, and total phenol contents (TPC), radical scavenging activity (RSA), and reducing power of the extracts were determined. The antioxidant activities of CP extracts increased as heating temperature increased. For example, heat treatment of CP at 150 degrees C for 60 min increased the TPC, RSA, and reducing power of EE from 71.8 to 171.0 microM, from 29.64 to 64.25%, and from 0.45 to 0.82, respectively, compared to non-heat-treated control. In the case of WE from CP heat-treated at the same conditions (150 degrees C for 60 min), the TPC, RSA, and reducing power also increased from 84.4 to 204.9 microM, from 15.81 to 58.26%, and from 0.27 to 0.96, respectively. Several low molecular weight phenolic compounds such as 2,3-diacetyl-1-phenylnaphthalene, ferulic acid, p-hydroxybenzaldoxime, 5-hydroxyvaleric acid, 2,3-diacetyl-1-phenylnaphthalene, and vanillic acid were newly formed in the CP heated at 150 degrees C for 30 min. These results indicated that the antioxidant activity of CP extracts was significantly affected by heating temperature and duration of treatment on CP and that the heating process can be used as a tool for increasing the antioxidant activity of CP.

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Egg white contains many functionally important proteins. Ovalbumin (54%), ovotransferrin (12%), ovomucoid (11%), ovomucin (3.5%), and lysozyme (3.5%) are among the major proteins that have high potentials for industrial applications if separated. The separation methods for these proteins from egg white have been developed since early 1900, but preparation methods of these proteins for commercial applications are still under development. Simplicity and scalability of the methods, use of nontoxic chemicals for the separation, and sequential separation for multiple proteins are very important criteria for the commercial production and application of these proteins. The separated proteins can be used in food and pharmaceutical industry as is or after modifications with enzymes. Ovotransferrin is used as a metal transporter, antimicrobial, or anticancer agent, whereas lysozyme is mainly used as a food preservative. Ovalbumin is widely used as a nutrient supplement and ovomucin as a tumor suppression agent. Ovomucoid is the major egg allergen but can inhibit the growth of tumors, and thus can be used as an anticancer agent. Hydrolyzed peptides from these proteins showed very good angiotensin I converting enzyme inhibitory, anticancer, metal binding, and antioxidant activities. Therefore, separation of egg white proteins and the productions of bioactive peptides from egg white proteins are emerging areas with many new applications.

Flavour comprises mainly of taste and aroma and is involved in consumers’ meat-buying behavior and preferences. Chicken meat flavour is supposed to be affected by a number of ante- and post-mortem factors, including breed, diet, post-mortem ageing, method of cooking, etc. Additionally, chicken meat is more susceptible to quality deterioration mainly due to lipid oxidation with resulting off-flavours. Therefore, the intent of this paper is to highlight the mechanisms and chemical compounds responsible for chicken meat flavour and off-flavour development to help producers in producing the most flavourful and consistent product possible. Chicken meat flavour is thermally derived and the Maillard reaction, thermal degradation of lipids, and interaction between these 2 reactions are mainly responsible for the generation of flavour and aroma compounds. The reaction of cysteine and sugar can lead to characteristic meat flavour specially for chicken and pork. Volatile compounds including 2-methyl-3-furanthiol, 2-furfurylthiol, methionol, 2,4,5-trimethyl-thiazole, nonanol, 2-trans-nonenal, and other compounds have been identified as important for the flavour of chicken. However 2-methyl-3-furanthiol is considered as the most vital chemical compound for chicken flavour development. In addition, a large number of heterocyclic compounds are formed when higher temperature and low moisture conditions are used during certain cooking methods of chicken meat such as roasting, grilling, frying or pressure cooking compared to boiled chicken meat. Major volatile compounds responsible for fried chicken are 3,5-dimethyl-1,2,4-trithiolanes, 2,4,6-trimethylperhydro-1,3,5-dithiazines, 3,5-diisobutyl-1,2,4-trithiolane, 3-methyl-5-butyl-1,2,4-trithiolane, 3-methyl-5-pentyl-1,2,4-trithiolane, 2,4-decadienal and trans-4,5-epoxy-trans-2-decenal. Alkylpyrazines were reported in the flavours of fried chicken and roasted chicken but not in chicken broth. The main reason for flavour deterioration and formation of undesirable “warmed over flavour” in chicken meat products are supposed to be the lack of α-tocopherol in chicken meat.

After far-infrared (FIR) radiation onto rice hull, a methanolic extract was prepared for the determination of antioxidant ability. After 30 min of FIR treatment, the radical scavenging activity and total phenol contents of rice hull extracts increased from 47.74 to 79.63% and from 0.12 to 0.19 mM, respectively, compared to control. Inhibition of lipid peroxidation in extracts was also increased from 41.07 to 47.96%. According to the GC-MS analysis, more phenolic compounds (p-coumaric acid, 3-vinyl-1-oxybenzene, p-hydroxybenzaldehyde, vanillin, p-hydroxybenzoic acid, and 4,7-dihydroxyvanillic acid) were detected in FIR-irradiated rice hull extract. These results indicated that FIR radiation onto rice hull could liberate and activate covalently bound phenolic compounds that have antioxidant activities.

Irradiation and high fat content accelerated the lipid oxidation in raw meat during storage. Oxygen availability during storage, however, was more important than irradiation on the lipid oxidation and color values of raw patties. Irradiated meat produced more volatiles than nonirradiated patties, and the proportion of volatiles varied by the packagingirradiation conditions of patties. Irradiation produced many unidentified volatiles that could be responsible for the off-odor in irradiated raw meat. No single volatile components but total volatiles, however, could be used to predict lipid oxidation status of raw meat. The results show that if patties are vacuumpackaged before irradiation and during storage, raw patties can be stored for 2 weeks without problems in lipid oxidation. Many volatile components produced by irradiation were not directly related to the lipid oxidation status of raw meat but were related to the irradiation odor. Identification of these components would shed light on the mechanisms and the source of the volatiles produced by irradiation ASL-R1525Summary and Implications Irradiation and high fat content accelerated the lipid oxidation in raw meat during storage. Oxygen availability during storage, however, was more important than irradiation on the lipid oxidation and color values of raw patties. Irradiated meat produced more volatiles than nonirradiated patties, and the proportion of volatiles varied by the packagingirradiation conditions of patties. Irradiation produced many unidentified volatiles that could be responsible for the off-odor in irradiated raw meat. No single volatile components but total volatiles, however, could be used to predict lipid oxidation status of raw meat.The results show that if patties are vacuumpackaged before irradiation and during storage, raw patties can be stored for 2 weeks without problems in lipid oxidation. Many volatile components produced by irradiation were not directly related to the lipid oxidation status of raw meat but were related to the irradiation odor. Identification of these components would shed light on the mechanisms and the source of the volatiles produced by irradiation.

The susceptibility of meats from different animal species (chicken breast [CB] and thigh [CT], pork [PL and beef [BL]) to lipid oxidation was studied. The amounts of TBARS in raw PL, CB, and CT did not change during a 7-d storage period. TBARS values of raw BL, however, significantly increased during 7-d storage because of high heme iron content, high lipoxygenase-like activities, and low 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activities. Ferric ion reducing capacities (FRC) were detected in all raw meats, but their characteristics were different: storage-unstable in CB and CT and storage-stable in PL and BL. Ferric ion reducing capacities in raw CB and CT was higher than those of PL and BL, and could be related to their high oxidative stability. The TBARS values of cooked meat increased significantly with storage. The rates of TBARS increase in cooked CT and BL were significantly higher than those of cooked CB and PL after a 7-d storage. Nonheme iron content in cooked BL was higher than other meats and increased significantly after 7 d. Cooked BL had a higher amount of heat-stable FRC, which acted as a prooxidant in the presence of high free ionic irons, than other meats. Therefore, high heat-stable FRC and increased nonheme iron content in cooked BL were responsible for its high susceptibility to lipid oxidation. Despite relatively low nonheme iron and heat-stable FRC levels, cooked CT showed similar levels of TBARS to cooked BL after a 7-d storage because of its high PUFA content.