Denise M. Smith

Composition, solubility and gel properties of salt soluble proteins from two bovine muscle types

The composition, pH solubility profile and thermal gelation behavior of two bovine muscles, vastus intermedius (VI, predominately red fibers) and semimembranosus (SM, predominantly white fibers) were compared. VI had a higher fat content and pH and lower protein content than SM. Between pH 5.2 and 5.8, the salt soluble proteins (SSP) from SM were more soluble than those from VI at the same pH, whereas solubilities above pH 6.0 were similar. Properties of SSP gels were measured at pH 5.5 and 6.1, the ultimate pH for SM and VI, respectively. Water lost from the VI gels due to syneresis was about 3 times greater than that lost from SM gels. VI gels prepared at pH 5.5 were firmer (p<0.05) than at pH 6.1, whereas deformability of SM gels at pH 6.1 were greater (p<0.05) than at pH 5.5. No differences (p>0.05) were observed between the firmness or deformability of VI or SM gels when compared at the same pH. Results suggest that ultimate muscle pH and fiber type do influence the properties of bovine SSP gels, although the effect is not as great as that previously reported for poultry muscle proteins.

Lactate dehydrogenase as safe endpoint cooking indicator in poultry breast rolls : development of monoclonal antibodies and application to sandwich enzyme-linked immunosorbent assay (ELISA)

A sandwich enzyme-linked immunosorbent assay (ELISA) was developed to detect lactate dehydrogenase (LDH) as a marker protein for verifying endpoint cooking of uncured poultry products. Monoclonal antibodies were prepared against chicken muscle LDH and used with rabbit polyclonal antibodies developed against turkey or chicken muscle LDH for capture and detection in the assay, respectively. Minimum assay detection limits for turkey and chicken muscle LDH were 1 ng/ml. Turkey and chicken muscle LDH, but not LDH from other species cross reacted in the ELISA. The ELISA was further verified using extracts of turkey breast rolls processed to internal temperatures between 68.3 and 72.1°C. The LDH content of extracts diluted 3- to 6-fold was below 15 ng/ml for turkey rolls processed to 70.9 and 72.1°C. At a 6-fold dilution, LDH content of extracts from rolls processed to 69.7°C was approximately 10 times greater than those processed to 70.9°C. A survey of market precooked poultry products indicated assay validity with precooked turkey roast, but not turkey hams with maximum internal temperature requirements of 68.3°C. Results suggested the sandwich ELISA should be applicable for determining whether turkey breast rolls are processed to the required U.S. Department of Agriculture endpoint temperature of 71.1°C.

Thermal inactivation of pathogens and verification of adequate cooking in meat and poultry products.

Publisher Summary This chapter discusses thermal inactivation of pathogens and verification of adequate cooking in meat and poultry products. The chapter reviews thermal processing as a means to eliminate microbial pathogens in meat and poultry. Besides discussing the evolution of thermal processing regulations in the US and listing official and alternative tests to verify compliance with the cooking requirements, an effort has been made to evaluate the advantages and disadvantages for each of the verification methods as well as the challenges to determine the thermal inactivation kinetics of microbial pathogens. The chapter reviews the thermal processing requirements currently implemented in the US; thermal inactivation of most common microbial pathogens found in meat and poultry products, and the use of thermometers, color determination, endpoint temperature indicators, and time-temperature integrators as means of verifying thermal processing adequacy.

Lactate dehydrogenase polyclonal antibody sandwich ELISA for determination of endpoint heating temperatures of ground beef

An enzyme-linked immunosorbent assay (ELISA) for the protein marker lactate dehydrogenase (LDH) was developed to determine endpoint heating temperature (EPT) of ground beef. Ground beef was placed in 10 by 75 mm tubes and heated to temperatures between 62 and 74°C at 2°C intervals. Electrophoresis and immunoblotting of meat extracts indicated a decrease in the intensity of the LDH band as temperature was increased. Polyclonal antibodies (PAb) against bovine muscle LDH were produced and a sandwich ELISA devised using biotinylated PAb as the detecting antibody. The LDH content decreased (P < 0.05) in ground beef heated between 66 and 74°C and was less than 4 μg/g of meat at the recommended minimum endpoint of 69°C. The ELISA was used to estimate the EPT of commercially cooked beef patties.

Production and characterization of a protein concentrate from navy beans (Phaseolus vulgaris)

Abstract Different methods were evaluated for the production of a navy bean protein concentrate (NPC). Most of the concentrates prepared by isoelectric precipitation contained 80–83% protein. Salt fractionation of the navy bean flour resulted in low concentrate yields. The most satisfactory method for production of a NPC from dry bean flour was a modification of the isoelectric precipitation method of Fan & Sosulski (1974) in which the centrifugation speed was increased to 15 000 × g. This concentrate had a protein content of 83·9% and a starch content of 2·4%. The concentrate contained more soluble protein and less phytohemagglutinin than the flour from which it was produced. The major protein was a 7S protein with three subunits of about 45–48 k Da typical of vicilin. About 10% of the protein present was in the form of a 60 kDa fraction.

Residual triose phosphate isomerase activity and color measurements to determine adequate cooking of ground beef patties

The objectives were to (i) compare the use of triose phosphate isomerase (TPI) activity and internal color scores for determination of cooking adequacy of beef patties and (ii) determine the effect of frozen storage and fat content on residual TPI activity in ground beef. Ground beef patties (24.4% fat) were cooked to five temperatures ranging from 60.0 to 82.2 degrees C. TPI activity decreased as beef patty cooking temperature was increased from 60.0 to 71.1 degrees C; however, no difference (P > 0.05) in activity (6.3 U/kg meat) was observed in patties cooked to 71.1 degrees C and above. Degree of doneness color scores, a* values and b* values, of ground beef patties decreased as internal temperature was increased from 60.0 to 71.1 degrees C; however, temperature had no effect on L* values. TPI activity in raw ground beef after five freeze-thaw cycles did not differ from the control. Three freeze-thaw cycles of raw ground beef resulted in a 57.2% decrease in TPI activity after cooking. TPI activity of cooked beef increased during 2 months of frozen storage, but TPI activity in ground beef stored for 3 months or longer did not differ from the unfrozen control. While past research has shown color to be a poor indicator of adequate thermal processing, our results suggest that undercooked ground beef patties could be distinguished from those that had been adequately cooked following U.S. Department of Agriculture guidelines using residual TPI activity as a marker.

Sucrose, sodium dodecyl sulfate, urea, and 2-mercaptoethanol affect the thermal inactivation of R-phycoerythrin

Thermal inactivation kinetics (D- and z-values) of the algal protein, R-phycoerythrin (R-PE), were studied under different buffer conditions (pH 4.0, 7.0, and 10.0) and concentrations of sucrose, sodium dodecyl sulfate (SDS), urea, and 2-mercaptoethanol (ME). R-PE solutions were heated in capillary tubes at temperatures between 40 and 90 degrees C depending on buffer conditions. Thermal inactivation parameters for R-PE, calculated on the basis of fluorescence loss, were modified by addition of chemicals. Overall, sucrose and ME had a thermostabilizing effect, while SDS and urea decreased thermal stability of R-PE. The z-values ranged from 5.9 degrees C in 50 mM NaCl, 20 mM glycine buffer, pH 10.0, to 37.8 degrees C in 60% sucrose, 50 mM NaCl, 20 mM phosphate buffer, pH 7.0. The z-values obtained for R-PE closely matched the z-values of some target microorganisms in food processes, suggesting R-PE might be used as a time-temperature integrator to verify thermal processing adequacy.

Changes in alpha-galactosidase activity and oligosaccharides during germination and incubation of cowpeas (Vigna unguiculata)

Abstract Germination of cowpeas at 24 and 30°C resulted in increased alpha-galactosidase activity during the first 6 to 12 h and leveled off subsequently. Stachyose content declined by 38% during 12 h of germination at 24°C. Incubation of a cowpea flour paste for 24 h at 24°C resulted in a large reduction of the stachyose and sucrose concentrations, and in their practical elimination at 34°C. Incubation for 12 h at 24 and 34°C of a cowpea paste made from 6-h germinated seeds resulted in a large decrease in stachyose content. Incubation of flour or germination of seeds effectively reduced the stachyose concentration of cowpeas.