Alden M. Booren

Formation and inhibition of heterocyclic aromatic amines in fried ground beef patties

The effect of vitamin E and oleoresin rosemary on heterocyclic aromatic amine (HAA) formation in fried ground beef patties was studied. Patties were fried at three temperatures (175 degrees C, 200 degrees C, 225 degrees C) for 6 and 10 min/side to determine the conditions for optimum HAA formation. HAAs were isolated by solid phase extraction and quantitated by HPLC. Greatest concentrations were generated when patties were fried at 225 degrees C for 10 min/side, 31.4 ng/g 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and 5.8 ng/g 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). Vitamin E, when used at two concentrations (1% and 10% based on fat content) and added directly to the ground beef patties, reduced PhIP concentrations in the cooked patties by 69% and 72%, respectively. Smaller but more variable reductions were achieved for MeIQx. Comparable inhibition of HAA formation was achieved by the direct addition of vitamin E (1% based on fat content) to the surface of the patties before frying. Concentrations of five HAAs studied were all significantly reduced (P<0.006), with average reductions ranging from 45% to 75%. Oleoresin rosemary, when used at two concentrations (1% and 10% based on fat content), reduced PhIP formation by 44%.

Effects of oxidised dietary oil and antioxidant supplementation on broiler growth and meat stability

1. Broilers were fed on diets containing oxidised sunflower oil, sunflower oil and sunflower oil supplemented with alpha-tocopherol, butylated hydroxyanisole (BHA) or butylated hydroxytoluene (BHT). 2. Oxidised oil caused a significant reduction in broiler body and carcase weights, whereas alpha-tocopherol and BHA/BHT supplementation improved growth. 3. Meat samples from these broilers were stored at 4 degrees C and -20 degrees C and their oxidative stability evaluated. Feeding oxidised oil to broilers resulted in meat that underwent rapid oxidative changes during refrigerated and frozen storage. 4. On the other hand, dietary alpha-tocopherol and BHA/BHT supplementation increased alpha-tocopherol and BHA/BHT concentrations in meat and significantly (P less than 0.05) improved the oxidative stability of meat during refrigerated and frozen storage.

Influence of oxidised dietary oil and antioxidant supplementation on membrane-bound lipid stability in broiler meat.

1. The effects of oxidised oil, dietary alpha-tocopherol and BHA/BHT-supplementation on the fatty acid composition of mitochondrial, microsomal and soluble protein fractions of broiler muscles, and on their lability to metmyoglobin/hydrogen peroxide-catalysed peroxidation were investigated. 2. Oxidised oil in the broiler diets induced rapid oxidation of the membrane-bound lipids and decreased their stability towards metmyoglobin-hydrogen peroxide-catalysed peroxidation. 3. Supplementation of the broiler diets with alpha-tocopherol increased the alpha-tocopherol concentrations in the microsomal and soluble protein fractions of the dark meat as well as the soluble protein fraction of the white meat. This, in turn, stabilised the membrane-bound lipids against metmyoglobin/hydrogen peroxide-initiated peroxidative changes.

Effect of salt on oxidative changes in pre- and post-rigor ground beef

Pre- and post-rigor beef was ground and salt was added to give 0·0, 0·5, 2·0 and 4·0% NaCl (w/w). Samples were removed after 0, 24, 48, 72 and 96 h at 4°C and analyzed for pH, TBA numbers and percentages of reduced myoglobin (Mb), metmyoglobin (MMb) and oxymyoglobin (MbO(2)). After holding for 96 h the samples were cooked in a boiling water bath to an internal temperature of 80°C and held at 4°C for 48 h before TBA analysis. Pre-rigor grinding and salting reduced the post-mortem pH decline and the extent of meat discoloration as shown by the differences in the amount of MMb. The extent of lipid oxidation as measured by TBA numbers was not significantly different for the pre- and post-rigor ground salted meat samples, although salt accelerated oxidation during storage. Results demonstrated that pre-rigor grinding and salting of beef produces a more stable bright red color, which appears to be associated with a lower percentage of MMb and a higher ultimate pH in the pre-rigor salted meat.

Improved oxidative stability of veal lipids and cholesterol through dietary vitamin E supplementation

The influence of dietary vitamin E supplementation on the α-tocopherol content of muscle membranes and on the resultant oxidative stability of veal was investigated. Daily supplementation of veal calves with 500 mg vitamin E in the form of α-tocopherol acetate for 12 weeks after birth increased muscle and membranal α-tocopherol concentrations approximately 6-fold over those of control animals. Oxidative stability of mitochondrial and microsomal lipids was enhanced by dietary supplementation as indicated by the results of an oxidative assay using hydrogen peroxide-activated metmyoglobin as the catalyst of oxidation. Muscle lipid and cholesterol stability was also improved by supplementation.

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.

Pork quality variation is not explained by glycolytic enzyme capacity

Our objective was to determine if increased glycolytic enzyme capacity accommodates rapid glycolysis, which leads to inferior pork color and water-holding capacity. Progeny from HAL-1843 free Duroc (n=16) or Pietrain (n=16) sires were harvested over a 2-week period. Coupled enzyme assays were used to quantify total capacity of pyruvate kinase (PK) and phosphofructokinase (PFK) in the sarcoplasmic fractions and crude homogenates of longissimus muscle (LM), respectively. Capacity of PK was not correlated with LM pH (20, 45, 180 min or 24 h), purge, drip loss, or CIE L* (P > 0.2). However, PFK capacity was inversely related to fluid loss (P<0.05). This finding was unexpected, but may result from PFK becoming partially denatured and inactivated by 20 min postmortem in samples that undergo a rapid pH decline. These data indicate that lighter pork color and reduced water-holding capacity are not associated with an increase in the capacity of enzymes that catalyze regulated steps of glycolysis.

Effect of Beef Product Physical Structure on Salmonella Thermal Inactivation

Numerous studies have assessed thermal inactivation of Salmonella in beef. However, the impact of muscle structure has been considered only recently, with several studies reporting enhanced thermal resistance in whole-muscle as compared to ground meat. The functional relationship between meat product physical structure and Salmonella thermal resistance has not been reported; therefore, it is not known whether thermal resistance is affected by the degree of grinding (that is, size of resulting particles). The objective of this study was to evaluate the relationship between thermal resistance of Salmonella and degree of grinding (whole-muscle, coarsely ground, finely ground, and beef puree). Each of the 4 product types was irradiated to sterility and inoculated with a marinade containing an 8-serovar Salmonella cocktail to achieve approximately 10(7.8) CFU/g. Samples (5 g each) were packed into sterile brass tubes, which were sealed, held at 60 degrees C in a water bath, and removed at 30 s intervals. Samples were then serially diluted and plated on Petrifilm aerobic count plates to enumerate surviving salmonellae. All samples had the same composition, thermal history, and initial Salmonella counts; therefore, differences in thermal resistance were due entirely to the degree of grinding. Overall, thermal resistance of Salmonella was highest (P < 0.0001) in whole-muscle (D = 2.7 min), but there were no differences among the 3 ground products (D(mean)= 1.2 min). Therefore, it would be prudent for Salmonella thermal inactivation models to consider whether a product is whole-muscle or ground, but not necessarily the degree of grinding. Practical Application: The results of this study suggest that thermal process validations for ready-to-eat meat products should also consider the structure of the product (which in this study was changed by the physical act of grinding). Salmonella was more resistant to heat in whole-muscle beef than in ground products; however, the degree of grinding did not affect the resistance.

Single directional migration of Salmonella into marinated whole muscle turkey breast

Irradiated, whole muscle turkey breasts were cut into blocks measuring 10 by 10 by 6 cm and exposed on one side to a marinade inoculated to contain a cocktail of eight Salmonella serovars at 10(8) CFU/ml. After exposure for 5, 10, or 20 min with or without vacuum (101.3 kPa), cylindrical cores perpendicular to the exposed surface were removed from the blocks with a hand-coring device and subdivided into 1-cm segments. Each segment was macerated, serially diluted in sterile peptone water, and plated to quantify Salmonella. Bacterial migration was greater under vacuum, compared with nonvacuum marination, at 20 min (P < 0.05). When all time levels were pooled within the vacuum and nonvacuum treatments, vacuum processing during marination increased bacterial migration into turkey breast (P < 0.05). This study provides evidence that if bacteria are present on the surface of the muscle, they could migrate into the intact muscle with or without the aid of vacuum.

Enhanced thermal resistance of salmonella in marinated whole muscle compared with ground pork.

The internal muscle environment may enhance thermal resistance of bacterial pathogens. Based on the migration of pathogens into whole muscle products during marination, the validity of current thermal inactivation models for whole muscle versus ground products has been questioned. Consequently, the objective of this work was to compare thermal resistance of Salmonella in whole muscle versus ground pork. Irradiated samples of whole and ground pork loin (5.5 to 7.5 g) were exposed to a Salmonella-inoculated (10(8) CFU/ml) marinade (eight serovar cocktail) for 20 min, placed in sterile brass tubes (12.7 mm diameter), sealed, and heated isothermally at 55, 58, 60, 62, or 63 degrees C, and surviving salmonellae were enumerated on Petrifilm aerobic count plates. The thermal lag times and initial bacterial counts were similar for both whole muscle and ground samples (P > 0.05), with all samples having equivalent compositions, inocula, and thermal histories. Heating temperature and physical state of the meat (whole versus ground muscle) affected Salmonella inactivation, with greater thermal resistance observed in whole than in ground muscle (P < 0.05). Assuming log-linear inactivation kinetics, Salmonella was 0.64 to 2.96 times more heat resistant in whole muscle than in ground pork. Therefore, thermal process validations for pork products should also account for the physical state of the product to ensure microbial safety.