A. M. Pearson

Improved resolution of myofibrillar proteins with sodium dodecyl sulfate-polyacrylamide gel electrophoresis

Standard experimental procedures for continuous polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate were modified to give more effective separation and improved resolution of myofibrillar proteins. The system utilizes a running gel consisting of 10% acrylamide with 0.1% bisacrylamide crosslinker (100:1) incorporating 400 mM Tris/glycine (pH 8.80), 0.1 mM ethylenediaminetetraacetate, 5% glycerol and 0.1% sodium dodecyl sulfate. Electrophoresis was performed at 1 mA per gel with corresponding running times of 4-6 h. The myosin heavy chain enters and migrates as a narrow symmetrical band while the smaller regulatory proteins of the myofibril are resolved. The utility of the procedure in relation to the study of protein structure is detailed.

Effects of synthetic antioxidants (BHA, BHT and PG) on the mutagenicity of IQ-like compounds☆

Abstract This study investigated the effects of the phenolic antioxidants (BHA, BHT and PG) on the mutagenicity of IQ, MeIQ and MeIQx by the Ames test. Results demonstrated that MeIQ, IQ and MeIQx were all mutagenic when tested with the Ames test with their potency being in the order listed above. This was true on testing with both TA98 and TA100, both of which required added S-9 for activation. It was clearly demonstrated that BHA and PG significantly inhibited the mutagenicity of IQ, MeIQ and MeIQx. On the other hand, BHT had little effect on the mutagenicity of IQ and MeIQ at low concentrations, but significantly increased their mutagenicity at high concentrations. BHT slightly inhibited the mutagenicity of MeIQx at all concentrations tested.

Role of triglycerides and phospholipids on development of rancidity in model meat systems during frozen storage

Abstract The effect of triglycerides, phospholipids and total lipids on development of rancidity during frozen storage at −18° C for 8 months was studied using lipid-free muscle fibres in combination with added triglycerides, phospholipids and total lipids. Results showed that added phospholipids greatly increased TBA values. Oxidation took place in two stages. Phospholipids were the first to oxidise, with their rate of oxidation decreasing with time. Oxidation of the triglycerides began only after a prolonged induction period. Results demonstrated that both triglycerides and phospholipids contribute to development of rancidity, although phospholipids make the greatest contribution. The influence of triglycerides on the development of rancidity was shown to depend upon the degree of unsaturation and the length of time in frozen storage. The relationship between oxidation of the polyunsaturated fatty acids (PUFAS) of the phospholipids and development of rancidity was confirmed.

Mechanisms by which nitrite inhibits the development of warmed-over flavour (WOF) in cured meat

Abstract The mechanism by which nitrite functions as an antioxidant in cured meat products was studied using ground beef and meat (beef) pigment extracts (MPE). Nitrite, l -ascorbate, sodium tripolyphosphate, ADP and EDTA were reacted with ground beef and MPE, after which the samples were heated and stored at 4°C. Lipid oxidation was assessed by the TBA method. The results suggested that nitrite functions as an antioxidant in three possible ways: (1) by the formation of a strong complex with heme pigments, thereby preventing the release of non-heme iron and its subsequent catalysis of lipid oxidation; (2) by interacting directly with the liberated non-heme iron (Fe2+) from denatured heme pigments and (3) to a lesser extent, by stabilization of the unsaturated lipids within the membranes. Stabilization of the porphyrin ring, preventing release of Fe2+ during the cooking process, appears to be the most important mechanism.

Relationship of mitochondria and sarcoplasmic reticulum to cold shortening.

Sarcoplasmic reticulum and mitochondria preparations from beef and rabbit muscle were shown to bind and release appreciable quantities of Ca(++). Differences between rabbit and beef muscle in Ca(++) binding and release by SR and mitochondrial preparations were not sufficient to account for the massive shortening in chilled beef as compared to little or no shortening in chilled rabbit muscle. Results substantiate the theory of Buege & Marsh (1975) that cold shortening is related to differences in mitochondrial concentration in red and white muscle rather than to differences in the Ca(++)-accumulating ability of SR. In order to explain the reversibility of cold shortening upon rewarming pre-rigor red muscle, a role for both SR and mitochondria is postulated and discussed.

Effects of length of frozen storage, cooking and holding temperatures upon component phospholipids and the fatty acid composition of meat triglycerides and phospholipids

Abstract Fatty acid profiles of triglycerides and phospholipids, and the levels of component phospholipids, were determined in beef and dark and light chicken meat at 0, 8 and 13 months of frozen storage at −18°C and again after cooking and holding at either 4°C or −18°C for 48h. There was a significant decline in the amount of PE (phosphatidyl ethanolamine) and PC (phosphatidyl choline) during frozen storage, but the decline was much greater upon cooking. PE and PC were also more stable following cooking upon holding at −18°C than at 4°C. Only minor changes occurred in the fatty acid profiles of the triglycerides during either freezer storage of the raw meat or subsequent storage after cooking. The drippings collected upon cooking contained largely triglycerides whereas PE was essentially absent, indicating that it was bound to the membranes. The increased proportion of PE in cooked meat, coupled with its susceptibility to oxidation, indicated that it may play a key role in the autoxidation of cooked meat.

Mechanism(s) involved in meat mutagen formation and inhibition.

The Maillard reaction, which involves Amadori rearrangement as a key step, also results in sugar fragmentation and free radical formation. The imidazoquinoline meat mutagens (2-amino-3-methylimidazo[4,5-f]-quinoline, or IQ, and 2-amino-3,4-dimethylimidazo[4,5-f]quinoline, or MeIQ) are formed from a reaction mixture containing alkylpyridine free radicals and creatinine. The imidazoquinoxaline meat mutagens (2-amino-3,4-dimethylimidazo[4,5-f]-quinoxaline, or MeIQx, and 2-amino-3,4,8-trimethylimidazo[4,5-f]-quinoxaline, or 4,8-DiMeIQx) may be produced by reacting a mixture containing dialkylpyrazine free radicals and creatinine. Two different pathways for free radical formation are proposed. One involves bimolecular ring formation from the enaminol form of the glycoaldehyde alkylimine and is followed by oxidative formation of the free radical. The other pathway involves formation of N,N1-dialkylpyrazinium ions from glyoxal monoalkylimine followed by reduction to produce the free radicals. The respective intermediates (glycoaldehyde alkylimine and glyoxal monoalkylamine) are formed by reacting glycoaldehyde and glyoxal with amino compounds. The glycoaldehyde system reacts faster and produces more free radicals than the glyoxal system. The reactions help to explain the formation of imidazoquinoxaline meat mutagens and their predominance in fried fish and why these mutagens are present in larger quantities in fried ground beef than the imidazoquinoline-type meat mutagens. These two pathways may not be the only mechanisms involved in formation of meat mutagens, but other free radical reactions may also contribute to meat mutagenicity and are mentioned briefly.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrite stabilization of lipids in cured pork

Peroxidation studies indicated that phospholipids, microsomes and mitochondria from cured pork samples are less susceptible to metmyoglobin/hydrogen peroxide-catalyzed peroxidation than their counterparts from nitrite-free pork samples. The reaction of phospholipids and polyunsaturated fatty acid ethyl esters with dinitrogen trioxide increased their stability to peroxidative changes. Phospholipids from cured pork and those lipids reacted with dinitrogen trioxide were capable of nitrosating a secondary amine. These data, together with infrared analyses, indicate that nitrite or dinitrogen trioxide reacts with unsaturated lipids to form nitro-nitroso derivatives, thus stabilizing the lipids toward peroxidation changes. This mechanism can, in part, explain the antioxidant role of nitrite in cured meats.

Some further observations on the TBA test as an index of lipid oxidation in meats

A modified TBA procedure utilizing an aqueous TBA solution to replace the acetic acid TBA reagent was tested with several meat samples. The modification prevented the formation of an interfering absorption peak at approximately 450 nm. The conversion factor for this method was determined to be 6·2. The method was further modified to allow the addition of TBHQ to raw and cooked samples prior to blending and heat distillation. The addition of 0·01% TBHQ (fat basis) significantly (p < 0·05) reduced TBA numbers of fish and chicken breast and raw chicken thigh meat, but did not significantly influence the TBA numbers for beef or cooked chicken thigh meat.

The role of nitrite in preventing development of warmed-over flavour

Abstract Development of warmed-over flavour (WOF) was followed in samples of beef, pork and chicken with and without added nitrite. Samples were evaluated by the 2-thiobarbituric acid (TBA) test and by sensory panel scores both before and after cooking at 0 days and again after storage for 48 h at 4°C. Added nitrite inhibited WOF development in cooked meat, resulting in a two fold reduction in TBA values for beef and chicken and a five fold reduction in pork. Sensory panel scores confirmed the protective effect of added nitrite in meat from all three species. Total lipid levels were not significantly related to WOF, but there was evidence for involvement of phospholipids.