Apple phenolics as inhibitors of the carbonylation pathway during in vitro metal-catalyzed oxidation of myofibrillar proteins.

The effect of apple phenolics on the oxidative damage caused to myofibrillar proteins by an in vitro metal-catalyzed oxidation system was investigated. Three pure phenolic compounds (chlorogenic acid, (-)-epicatechin and phloridzin) and an apple peel extract were added to myofibrillar proteins in three concentrations (50, 100 and 200µM), and a blank treatment was included as a control. All suspensions were subjected to Fe(3+)/H2O2 oxidation at 37°C during 10days, and protein oxidation was evaluated as carbonylation (α-amino adipic and γ-glutamic semialdehydes) and Schiff base cross-links. Significant inhibition by apple phenolics was found as compared to the control treatment, with (-)-epicatechin being the most efficient antioxidant and phloridzin showing the weakest antioxidant effect. The higher concentrations of apple extract showed effective antioxidant activity against protein oxidation in myofibrillar proteins, emphasizing the potential of apple by-products as natural inhibitors of protein oxidation in meat products.

Influence of the Oxidation States of 4-Methylcatechol and Catechin on the Oxidative Stability of ß-Lactoglobulin.

Chemical interactions between proteins and phenols affect the overall oxidative stability of a given biological system. To investigate the effect of protein-phenol adduct formation on the oxidative stability of ß-lactoglobulin (ß-LG), the protein was left to react with an equimolar concentration of 4-methylcatechol (4MC), catechin (Cat), or their respective quinone forms, 4-methylbenzoquinone (4MBQ) and catechin-quinone (CatQ), and subsequently subjected to metal-catalyzed oxidation by Fe(II)/H2O2 for 20 days at 37 °C. The reaction with 4MBQ resulted in 60% thiol loss and 22% loss of amino groups, whereas the addition of 4MC resulted in 12% thiol loss. The reaction with Cat or CatQ resulted in no apparent modification of ß-LG. The oxidative stability of ß-LG after reaction with each of 4MC, 4MBQ, Cat, or CatQ was impaired. Especially 4MC and 4MBQ were found to be pro-oxidative toward α-aminoadipic semialdehyde and γ-glutamic semialdehyde formation as well as the generation of fluorescent Schiff base products. The changes observed were ascribed to the redirection of oxidation as a result of the blocking of thiol groups but also to the oxidative deamination pathway, accelerating the production of semialdehydes and subsequently Schiff base structures.

Protein oxidation during frozen storage and subsequent processing of different beef muscles.

This study examined the relationship between protein and lipid oxidation and the impairment of the water holding capacity (WHC), redness and instrumental hardness occurring during 20 weeks of frozen storage (-18 °C) and subsequent processing (cooking, chilled storage) of psoas major, quadriceps femoris and longissimus dorsi beef patties. Patties were analyzed at sampling times upon thawing (weeks 0, 4, 8, 12 and 20) for lipid (TBARS, hexanal) and protein oxidation products (α-aminoadipic and γ-glutamic semialdehydes, α-aminoadipic acid, Schiff bases). A significant impact of frozen storage on protein oxidation was found, which occurred concomitantly with a loss of WHC, redness and significant changes in the hardness of cooked patties. Heme-iron, endogenous antioxidant enzymes and to a lower extent, fatty acid composition, played a role in the oxidative stability of patties. Plausible mechanisms by which particular protein oxidation changes may lead to loss of WHC and impaired quality traits were discussed.

Temperature of frozen storage affects the nature and consequences of protein oxidation in beef patties.

The effect of three frozen storage temperatures (-8, -18 and -80 °C) on protein oxidation in beef patties was studied through the analysis of novel oxidation markers. Additionally, the connection between lipid and protein oxidation and the impact of the latter on particular quality traits (water holding capacity, color and texture) of subsequently processed beef patties (cooking/cold-stored) were investigated. Protein oxidation was measured as the loss of tryptophan fluorescence and formation of diverse lysine oxidation products (α-aminoadipic semialdehyde, α-aminoadipic acid and Schiff bases). Lipid oxidation was assessed by levels of thiobarbituric acid reactive substances and hexanal. A significant effect of storage temperature on protein oxidation was detected. Frozen storage increased the susceptibility of meat proteins to undergo further oxidation during processing. Timely interactions were found between lipid and protein oxidation. Plausible mechanisms by which oxidative damage to proteins may have an impact in particular quality traits are thoroughly discussed.

Impact of high pressure treatment and intramuscular fat content on colour changes and protein and lipid oxidation in sliced and vacuum-packaged Iberian dry-cured ham.

The effect of high hydrostatic pressure (HHP) (600MPa) and intramuscular fat content (IMF) on colour parameters and oxidative stability of lipids and proteins in sliced vacuum-packaged Iberian dry-cured ham during refrigerated storage (120 days at 2°C) was investigated. Several studies have investigated the influence of HHP on lipid oxidation of meat products. However, its effects on protein carbonylation, as also the influence of IMF content on this carbonylation are poorly understood. HHP treatment had a significant effect on lean lightness after 0 and 120 days of storage while IMF content increased lightness and yellowness over time. Regarding oxidative stability, the effect of HHP treatment depended on IMF content samples with a high IMF having greater lipid instability while samples with a low IMF underwent more protein carbonylation.

Impact of trolox, quercetin, genistein and gallic acid on the oxidative damage to myofibrillar proteins: the carbonylation pathway.

The carbonylation pathway involves the oxidative deamination of lysine residues to yield a carbonyl compound (α-aminoadipic semialdehyde) that can be further oxidised to α-aminoadipic acid and form Schiff bases structures. The effect of trolox and other phenolic compounds (PhC) (namely genistein, quercetin and gallic acid) on the protein carbonylation pathway occurred during the oxidation of myofibrillar proteins (MP) catalysed by a Fe(3+)/H2O2 system was studied. Trolox and PhC can exert either antioxidant or pro-oxidant capacities depending on their concentration, the oxidation conditions and the target in proteins. In general, quercetin and genistein showed an antioxidant activity towards lipid oxidation and the carbonylation pathway at different concentrations under the analysed conditions. Plausible mechanisms for the antioxidant and pro-oxidant effects of trolox and PhC on MP are discussed. Further research is needed to shed light on the effect of PhC mixtures on both lipid and protein oxidation.

Oxidative damage to poultry, pork, and beef during frozen storage through the analysis of novel protein oxidation markers.

The susceptibility of meats from different animal species (beef quadriceps femoris, porcine longissimus dorsi, and chicken pectoralis major) to undergo protein oxidation during frozen storage (20 weeks/-18 °C) was studied through the analysis of novel oxidation markers. Frozen storage induced protein carbonylation (α-aminoadipic and γ-glutamic semialdehydes), carboxylation (α-aminoadipic acid), and formation of Schiff bases in meat from the three species. Major rates of protein and lipid oxidation products [thiobarbituric-acid-reactive substances (TBARS) and hexanal] were found in beef patties. Among the endogenous factors having a potential influence on the susceptibility of meat to undergo protein oxidation, heme iron seemed to play a major role. The present study illustrates the severe chemical modifications induced by oxidative stress during frozen storage of ground meat and provides original insight into the underlying mechanisms and factors.

Oxidation of myofibrillar proteins and impaired functionality: underlying mechanisms of the carbonylation pathway.

The potential impact of protein oxidation on the functional properties of myofibrillar proteins (MP) was investigated in the present study. To accomplish this purpose, myofibrillar proteins were oxidized in vitro for 12 days at 37 °C in the presence of Cu(2+), Fe(3+), and Mb in combination with H(2)O(2) and analyzed at sampling times for chemical changes induced by oxidative reactions and functional properties. The oxidation measurements included specific protein carbonyls (α-aminoadipic semialdehyde, AAS), advanced lysine oxidation products (α-aminoadipic acid, AAA, and Schiff bases), and thiobarbituric acid-reactive substances (TBARS). The factors and mechanisms involved in the oxidative degradation of lysine residues through the carbonylation pathway are precisely described. According to the present results, intense lipid and protein carbonylation, principally induced by Cu(2+)/systems, leads to a fast and severe loss of MP functionality, including impaired water-holding, foaming, and gelling capacities. The implication of Mb in the oxidation events enhances the production of AAA and Schiff bases, compromising to a larger extent the solubility of MP and worsening the aggregation and the gelling capacity. The connection between the oxidation-induced chemical changes and the loss of protein functionality is thoroughly discussed.

Formation of lysine-derived oxidation products and loss of tryptophan during processing of porcine patties with added avocado byproducts.

The effects of the addition of avocado oil and a phenolic-rich avocado peel extract on protein oxidation were studied in porcine patties subjected to cooking and chilled storage. Protein oxidation was assessed by means of tryptophan loss and the formation of specific lysine oxidation products, such as α-aminoadipic semialdehyde (AAS), α-aminoadipic acid (AAA), and Schiff bases. In the present paper, quantitative data of AAA are reported for the first time on a food matrix. The addition of the avocado extract inhibited the formation of AAS, AAA, and Schiff bases in patties during cooking and subsequent chilled storage. The antioxidant effect may respond to the protecting effect of phenolic compounds, mainly procyanidins, found on the avocado extract. Apparently, the combination of both strategies (back-fat replacement and addition of avocado extract) does not lead to an enhanced advantage on the oxidative stability of the product. The novel methodologies used in the present study enable a better comprehension of the mechanisms and consequences of protein oxidation in food systems.

Dog rose (Rosa canina L.) as a functional ingredient in porcine frankfurters without added sodium ascorbate and sodium nitrite.

The effect of dog rose (Rosa canina L.; RC), rich in polyphenols and ascorbic acid, on lipid and protein oxidation, colour stability and texture of frankfurters was investigated. Four treatments were prepared: with 5 or 30 g/kg RC extract and without sodium ascorbate and sodium nitrite (5RC and 30RC, respectively), a positive control (with sodium ascorbate and sodium nitrite; PC) and a negative control (without sodium ascorbate, sodium nitrite or RC extract; NC). Hexanal values were much higher throughout storage in NC compared to RC and PC frankfurters (P<0.001). The RC extracts protected against protein oxidation, but not as efficiently as PC (P<0.05). In the RC treated frankfurters, lower a* values were measured compared to PC due to the lack of sodium nitrite. In conclusion, dog rose can act as a natural antioxidant in frankfurters, but not as full replacer for sodium nitrite.

Fluorescent HPLC for the detection of specific protein oxidation carbonyls - α-aminoadipic and γ-glutamic semialdehydes - in meat systems.

Precise methodologies for the routine analysis of particular protein carbonyls are required in order to progress in this topic of increasing interest. The present paper originally describes the application of an improved method for the detection of α-aminoadipic and γ-glutamic semialdehydes in a meat system by using a derivatization procedure with p-amino-benzoic acid (ABA) followed by fluorescent high-performance liquid chromatography (HPLC). The method development comprises i) the description of a simple HPLC program which allows the efficient separation of the ABA and the key standard compounds and ii) the optimization of the procedure for the preparation of a meat sample in order to maximize the fluorescent signal for both protein carbonyls. Furthermore, the suitability of this method is evaluated by applying the technique to porcine burger patties. The present procedure enables an accurate and relatively fast analysis of both semialdehydes in meat samples in which they could play an interesting role as reliable indicators of protein oxidation.