Carbonylation of myofibrillar proteins through the maillard pathway: effect of reducing sugars and reaction temperature

Reactive carbonyl-scavenging ability of 2-aminoimidazoles: 2-amino-1-methylbenzimidazole and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

The carbonyl-scavenging ability of 2-amino-1-methylbenzimidazole (AMBI) and the heterocyclic aromatic amine 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was investigated in an attempt to identify new routes that can modify the carbonyl content of foods. The reaction of both AMBI and PhIP with 2-alkenals, 2,4-alkadienals, 4-oxo-2-alkenals, 4,5-epoxy-2-alkenals, and 4-hydroxy-2-nonenal produced fluorescent adducts, whose structure was determined for the adduct produced between AMBI and 2-pentenal. This adduct was isolated and identified by one- and two-dimensional nuclear magnetic resonance and high-resolution mass spectrometry as 2,10-dihydro-2-ethyl-10-methylpyrimido[1,2-a]benzimidazole. The formation of these adducts was parallel to the elimination of AMBI and PhIP. The Ea of the reaction between PhIP and 4-oxo-2-nonenal was 27.4 kJ/mol. All these results suggest that 2-aminoimidazoles can be employed to modify the carbonyl content of foods. At the same time and because the reaction produces the disappearance of the amino compound, lipid-derived carbonyl compounds can be employed to eliminate 2-aminoimidazoles, which suggests a new strategy for the elimination of heterocyclic aromatic amines in foods.

Effect of cooking on meat proteins: mapping hydrothermal protein modification as a potential indicator of bioavailability

Thermal treatment of meat proteins induces a range of observable and molecular-level changes. In order to understand and track these heat-induced modifications at the amino acid level, various analytical techniques were used. Changes were observed both in the soluble and in the insoluble fractions after hydrothermal treatment of minced beef samples. Redox proteomics clearly indicated increasing oxidative modification of proteins with increased heat exposure. Collagens in the soluble fraction and myosin in the insoluble fraction were found to be highly susceptible to such modifications. Maillard reaction products in the insoluble and pyrrolidone formation in the soluble fraction steadily increased with increased heat exposure. Fluorescence studies indicated a rapid increase in fluorescence with heat, suggesting the formation of advanced glycation end products. Overall these results provide a deeper understanding of the effect of cooking on meat proteins and the possible relationship to processing conditions in meat-derived food.

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.