Effect of Heating Temperature and Muscle Type on Porcine Muscle Extracts as Determined by Reverse Phase High Performance Liquid Chromatography

Samples from porcine longissimus muscles were heated to temperatures ranging from 40–80°C to reach endpoint temperatures (0 min) or held at endpoint temperature for 30 min. Proteins in water-soluble extracts of these samples were separated and quantified by reverse phase high performance liquid chromatography (RP-HPLC). After heating to 60°C for 0 min or to 55°C and holding for 30 min, lactate dehydrogenase (LDH), pyruvate kinase (PK) and myoglobin appeared to comprise the bulk of the remaining soluble protein. RP-HPLC analysis of water soluble extracts from longissimus dorsi, serratus ventralis and psoas major muscles from barrows and sows indicated differences in proportions of LDH and myoglobin.     

Cooking Temperature of Turkey Ham Affects Lactate Dehydrogenase, Serum Albumin and Immunoglobulin G as Determined by ELISA

Protein indicators were identified and enzyme-linked immunosorbent assays (ELISA) were developed for verifying endpoint processing temperatures (EPT) of turkey ham. Lactate dehydrogenase (LDH), immunoglobulin G (IgG), and turkey serum albumin (TSA) were identified by electrophoresis, Western blotting or enzyme assays as potential markers in turkey ham processed between 66.9 and 73.9°C. TSA and IgG were quantified using indirect competitive ELISAs, and LDH was quantified by a sandwich ELISA. The concentration of all indicators decreased as processing temperatures were increased. At 73.8°C, 9.3 μg TSA and, 0.5 μg LDH or TSA were detected/g meat. At the USDA required EPT of 68.3°C, residual concentrations of 1221 ng IgG/g meat, 330 ng LDH/g meat and 51,852 ng TSA/g meat were detected.     

Kinetic and Thermodynamic Parameters for Heat Denaturation of Bovine Milk IgG, IgA and IgM

For heat denaturation of bovine milk immunoglobulins (IgG, IgA and IgM) in the temperature range 62 to 81°C, the D values were IgG > IgA > IgM at any temperature. The Z values were 6.29, 4.00 and 5.17°C for IgG, IgA and IgM, respectively. Heat denaturation of bovine milk immunoglobulins followed a reaction kinetics in the order of n= 1.5. The highest value for apparent energy of activation was observed for IgA, and the lowest for IgG. Bovine milk immunoglobulins could resist the HTST pasteurization treatment at 72°C for 15 sec without affecting their structure.     

Compositional Factors that Influence Lipid Peroxidation in Beef Juice and Standard Sausages

In order to identify how different additives influenced lipid peroxidation formation, a sausage only using beef juice as pigment source and a standard beef–pork meat sausage were studied. The effects of different additives, including fish oil, myoglobin, nitrite, clove extract, and calcium sources on oxidation and sensory properties were examined. Both sausage systems were stored in 3 different manners prior to testing: (1) frozen immediately at ?80 °C; (2) chilled stored for 2.5 weeks followed by fluorescent light illumination at 4 °C for another 2 wk; (3) frozen at ?20 °C for 5 mo. The frozen group 3 showed the highest peroxide formation and thiobarbituric acid reactive substances (TBARS) for both sausage systems. Unpolar peroxides dominated in both systems. The clove extract could offset the peroxide formation from myoglobin/beef juice and/or fish oil, but the addition of clove flavor was recognized by the sensory panelists. Calcium addition reduced lipid peroxide formation. Added nitrite and fish oil seemed to interact to stimulate nitroso‐myoglobin formation. Nitrite was identified to interact with clove addition and thereby, relatively speaking, increased TBARS. The 2 sausage systems generally ranked the additives similarly as pro– and antioxidants.     

Stability of Membrane-Sterilized Bovine Immunoglobulins Aseptically Added to UHT Milk

Lyophilized immunoglobulin (IgG) of 56% purity isolated from Cheddar cheese whey was reconstituted with distilled water to a protein content of 60–70 mg/mL. The solution was membrane-sterilized (0.2 μ.m) and aseptically injected into cartons of UHT milk. This method could be used for fortification of UHT products without denaturing IgG. Concentration of IgG remained constant in milk stored at 4, 25 and 35°C over 5 mo. However, when stored at 25 and 35°C, the milk thinned probably due to residual enzymes in the IgG solution. D values measured between 62 and 80°C for thermal destruction of IgG in UHT milk appeared to confirm shelf life results.     

Determination of Metmyoglobin Reductase Activity in Bovine Skeletal Muscles

A novel technique was used to obtain an isolate of skeletal muscle containing MetMb reductase. The isolate was then used as the enzyme source in an assay procedure to measure specific MetMb reductase activity. Enzyme activity was highest at pH 6.4 as compared to 5.8 or 7.0 and at 30°C compared to 4°C. Significant differences in enzyme activity were found among beef muscles from the same animal. The order of muscles, when enzyme activity was expressed on the basis of muscle myoglobin content, was: tensor faciae latae > longissimus dorsi > gluteus medius > diaphragma medialis > semimembranosus = psoas major (p = 0.01).     

Microbiology of a Ham-Type Product Made from Soy-Extended Cured Beef and Inoculated with Clostridium sporogenes PA3679

The microbiological stability of a new ham-type product made from soy-extended cured beef was examined under wholesale (2–4°C) and retail (5°C) refrigerated storage conditions, and during abuse-temperature holding for 24 and 48 hr at 24-25°C after inoculation with Closrridium sporogenes PA3679. No microbiological effects (P >0.05) could be attributed to the level of soy protein isolate in the injection brine (0, 5, 7.5 or 9%) on the basis of mesophilic, psychrotrophic, anaerobic and lactic bacterial counts. Samples held at 2-4°C did not exceed 10⁴ CFU/g after 4 wk for any bacterial type examined. Product shelf-life was > 3 wk at 5°C and 2 wk at 8–10°C. Inoculated PA3679 did not grow in the product during 24 or 48 hr simulated mishandling (24-2°C).     

Selective Concentration of Bovine Immunoglobulins and α-Lactalbumin from Acid Whey using FeCl3

Immunoglobulins and α-lactalbumin of acid whey were concentrated in supernatant and precipitate when FeCl₃ was added at pH 4.2 and 2.8, respectively. Optimized conditions of pH 4.2 were preferable because of higher retention of immunochemical activity of immunoglobulins. In acid whey treated with 7.5 mM FeCl₃ at pH 4.2 and 4°C, 90% of β-lactoglobulin coprecipitated with serum albumin while 70% of immunoglobulins (92% immunochemically active IgG) and 95% of α-lactalbumin were retained in the supernatant. More than 98% of added iron was subsequently eliminated as precipitate by holding the treated whey at pH 8-9 and 4°C, without losing immunochemical activity of immunoglobulin G, in addition to retained activity of immunoglobulins A and M.     

Accelerated Kinetic Study of Aspartame Degradation in the Neutral pH Range

The degradation of aspartame in solution as a function of temperature (70–100°C), buffer concentration (0.01–0.1M phosphate), and pH (6–7) was studied in order to estimate losses during thermal processing and storage of aseptic milk-based drinks. Prior data have been mostly on acid carbonated beverages. First order rate constants were obtained in all the conditions with activation energies in the range 14–20 kcal/ mole. An increase in both pH and buffer concentration caused an increase in rate of loss. These data were used to predict losses that would occur during pasteurization and sterilization conditions. Experiments at 4 and 30°C showed significant losses would occur during 4 and 30°C temperature storage and extrapolation from high temperatures predicted faster degradation rates than those found.     

Effect of heat and autoclave on allergenicity of porcine serum albumin

This study was performed to investigate the effects of heat and autoclave treatment on the binding ability of porcine serum albumin (PSA) to IgG and the serum of patients who were allergic to pork. Heat treatment at 100°C for 20 min on PSA was able to decrease the binding ability of PSA to IgG to 52%. The binding ability of PSA to IgG was also reduced to 29% by autoclave treatment of PSA at 121°C for 30 min. The binding ability of PSA autoclaved for 30 min to serum also decreased to 10%. SDS-PAGE and immunoblotting of PSA heated at 100°C for 20 min revealed that the intensity of the PSA band decreased and its presence was barely recognized by IgG. In the case of autoclave treatment (for 5 min), PSA was degraded to low-molecular-weight peptides and IgG and serum did not recognize them. Therefore, autoclave treatment can effectively reduce the allergenicity of PSA.     

Lactate Dehydrogenase Activity as an Endpoint Heating Indicator in Cooked Beef

Lactate dehydrogenase (LDH, E.C. 1.1.1.27) activity, specifically LDH5 isoenzyme, declined significantly when bovine Semimembranosus (SM) slurries were heated from 57° to 66°C. When SM whole muscle roasts were brine pumped and oven-cooked, total LDH and specific activities declined proportionately from 57° to 63°C resulting in almost no activity at 63°± 0.5°C. LDH activities were consistently higher in younger cattle and lower in older cattle for SM, Infraspinatus (IN) and Longissimus dorsi (LD) muscles and were lowest overall in the IN. LDH colorimetric and fluorescent assays were more accurate indicators for predicting beef roast heating temperature endpoints between 60° and 63°C than the USDA-FSIS method.     

Influence of Dairy Proteins on Aspartame Stability in the pH 6–7 Range

The effect of three commercial milk protein products on aspartame degradation was studied as a function of temperature (4, 30, 70, 80°C), pH (6 and 7), phosphate buffer concentration (0.01 M/L, 0.1 M/L) and protein (0–3%). Caseinates significantly decreased the pseudo-first order loss rate at low buffer concentration and higher temperature (70–80°C), whereas the rate was faster in the presence of a casein/ whey mixture. At high buffer concentration, the loss rate was not affected by protein. The protective effect may have been due to either a buffering capacity decrease caused by a protein/aspartame interaction that lowered pH or some unknown protein interaction. At 4 and 30°C, the loss rate was not affected by calcium caseinate.     

Heat-resistant structural features of bovine β-lactoglobulin A revealed by NMR H/D exchange observations

The thermal unfolding of the A variant of bovine β-lactoglobulin (β-Lg), in 50 mm phosphate buffer at pH 3.0, was followed by nuclear magnetic resonance (NMR) hydrogen/deuterium (H/D) exchange observations. The exchange behaviour of a large number of backbone amide protons (H_Ns) was monitored at temperatures between 37°C and 80°C to determine the relative thermal stability of different elements of the native protein structure. The H/D exchange was rapid at 37°C for the H_Ns on the residues in loops and in the terminal regions of the native protein. Further H/D exchange was promoted by heat treatment at temperatures up to 80°C and was completed for the identifiable H_N of the various α and β structural elements in the following order: D–E strand (55–60°C); C–D strand and α-helix (60–65°C); A–B, A–I and E–F strands (65–70°C); and A–H, B–C and F–G strands (75–80°C). At 80°C, the only identifiable H_N signal was from F105 which indicated that the G–H pair of disulphide-linked strands formed the most heat-resistant feature of the β-Lg structure. The effect of heating to 80°C was shown to be largely reversible by subsequent D/H exchange and sodium dodecyl sulphate polyacrylamide gel electrophoresis. Interestingly, the susceptibility of particular H_Ns to H/D exchange was found to correlate reasonably well with the susceptibility to tryptic hydrolysis.     

Effect of debranching and heat treatments on formation and functional properties of resistant starch from high-amylose corn starches

High-amylose corn starches [(Hylon V (H5) and Hylon VII (H7)] were debranched with pullulanase, followed by autoclaving–storing cycles and drying in an oven (at 50 °C) or freeze-dryer. The samples were autoclaved at 123 and 133 °C and stored at 4 and 95 °C. Molecular weights of the samples decreased and resistant starch (RS) contents increased with increased debranching time. RS contents of H7 samples were higher than those of H5 samples. RS contents of oven-dried samples were higher than those of freeze-dried samples. Debranching caused decreases in DSC peak temperature (T _p) and increases in enthalpy (ΔH) values of H5 and H7. Autoclaving at 133 °C caused higher ΔH values as compared to autoclaving at 123 °C. The solubility and water-binding values of autoclaved-only (control) and autoclaved–debranched (3–48 h) samples and the samples treated with autoclaving–storing cycles after debranching of both H5 and H7 were higher than those of their respective native starches. Debranching of starch samples affected the emulsion capacity of albumin adversely, but improved the emulsion stability of albumin. Cold viscosity values of freeze-dried samples were higher than those of oven-dried samples. Autoclaving–storing cycles after debranching caused decreases in peak, breakdown and final viscosity values.     

The Effect of Heat Treatment on Anilinonaphthalene-8-Sulphonate Binding to Rapeseed Albumin (Napin)

Protein surface hydrophobicity can be measured by the fluorescent probe method. The effect of heat treatment on Brassica napus (rapeseed) albumin (napin) interactions with a fluorescent probe, anilinonaphthalene-8-sulphonic acid (ANS) was investigated by fluorescent titration. Upon heating to 100°C for 30 min the number of napin binding sites for ANS (n) increased from 5(±0·7) to 13(±0·5) moles of ANS bound per mole of protein. The ANS-protein dissociation constant (Kd) was 2·0(±0·4)×10^-6 M for the unheated protein and 10·4(±0·1)×10^-6 M for heat-denatured napin. There was also a blue shift in the fluorescence emission spectrum maximum for denatured napin–ANS complex consistent with an increase in the hydrophobicity of the ANS binding sites in the denatured protein. The characteristic fluorescence increase for heat-denatured albumin–ANS mixtures is therefore due to an increase in the number, binding affinity and hydrophobicity of binding sites. Heat treatment of napin leads to the appearance of additional surface hydrophobic sites in the denatured protein. © 1997 SCI.     

Functionality and Microbial Stability of Ultrapasteurized, Aseptically Packaged Refrigerated Whole Egg

Raw, liquid whole egg was ultrapasteurized and aseptically packaged to extend the refrigerated shelf-life and maintain functional quality. Nine processes ranged from 63.7–72.2°C for 2.7 to 192.2 sec and resulted in shelf-lives ranging from 4 to >24 weeks at 4°C. Egg pasteurized by an essentially conventional process (26.2 set, 63.7°C), aseptically packaged and stored at 4°C spoiled in 4–8 weeks. Overall, little or no change was observed in the chemical (protein and solids contents, soluble protein, pH) and functional properties (performance in cakes and custards) of the ultrapasteurized, aseptically packaged, 4°C refrigerated egg compared to raw egg. Egg of acceptable quality may be produced by this process with a 3–6 months shelf-life at 4°C.     

Enzymatic Production of Ribonucleotides from Autolysates of Kluyveromyces marxianus Grown on Whey

After 20h fermentation of medium containing 5% (w/v) dehydrated whey, at 30°C, pH 4.5, yeast cells were harvested, diluted in 0.1M KH₂PO₄, and autolyzed at different pHs (6.5–7.5) and temperatures (45–55°C). Phosphodiesterase (0.2–1.0% w/v, 65°C, pH 6.5, 6h) and adenyl deaminase (0.5-1.0% w/v, 60°C, pH 5.5, 4h) were added to the autolysates. After heat treatment (100°C, 15 min), samples were analyzed by RP-HPLC and LC/MS. Production of 5′-ribonucleotides was maximized at 50°C, pH 6.5. Yields of 5′-AMP (800 μg/g of biomass) and 5′-GMP (2000 μg/g) increased considerably after addition of 1.0% phosphodiesterase. 5′-IMP increased only after addition of 1.0% adenyl deaminase.     

Effect of High Hydrostatic Pressure and Temperature on Enzymatic Activity and Quality Attributes in Mango Puree Varieties (cv. Tommy Atkins and Manila)

Pectinmethylesterase (PME), peroxidase (POD), and polyphenoloxidase (PPO) residual activities (RAs) and physicochemical parameters (pH, total soluble solids (TSS), water activity (a_w), viscosity and color) of Tommy Atkins and Manila mango purees (MPs) were evaluated after high hydrostatic pressure (HHP) treatments at 400–550 MPa/0–16 min/34 and 59 °C. HHP treatment applied at 59 °C induced higher enzyme inactivation levels than the treatment applied at 34 °C in both MPs. The lowest RA of PME (26.9–38.6%) and POD (44.7–53%) was achieved in Manila MP treated at 450 MPa/8–16 min/59 °C and 550 MPa/4–16 min/59 °C, respectively. Otherwise, Tommy Atkins puree pressurized at 550 MPa/8–16 min/59 °C had the lowest PPO RA (28.4–34%). A slight decrease in pH and TSS values of both HHP-processed MPs at 34 and 59 °C was observed, whereas the a_w remained constant after processing. The viscosity of MPs tended to augment up to 2.1 times due to the application of HHP. No significant changes were observed in color parameters of Tommy Atkins MP, except at 550 MPa and 59 °C where higher yellow index (YI) (122.4?±?3.3) and lower L* (37.3?±?5.3) were obtained compared to the untreated MP. HHP caused an increase in L* values in Manila MP, whereas no clear trend was observed in YI. HHP processing at 550 MPa combined with mild temperature (59 °C) during 8 min could be a feasible treatment to reduce enzymatic activity and preserve fresh-like quality attributes in MP.     

Injury,Inhibition and Inactivation ofEscherichia coli O157:H7 by Potassium Sorbate and Sodium Nitrite as Affected by pH and Temperature

The effect of potassium sorbate (0–2 g litre⁻¹) and sodium nitrite (0–1 g litre⁻¹) on the growth of four strains of Escherichia coli O157: H7 in tryptic soya broth at various pH levels (pH 4·0–7·0 for sorbate, pH 5·0–8·0 for nitrite) were determined at 37°C and 4°C. Among the pH levels tested, sorbate and nitrite exhibited the highest antimicrobial activity at pH 4·0 and 5·0, respectively. At pH 5·0 and 37°C, the presence of 500 mg litre⁻¹ sorbate or 200 mg litre⁻¹ nitrite completely inhibited the growth of E coli O157: H7. While at higher pH levels, 2 g litre⁻¹ sorbate or 1 g litre⁻¹, nitrite, the highest concentration tested, did not show significant antimicrobial action against the test organisms. At 4°C and pH 5·0, the inoculated test organisms did not showed any significant growth in preservative-free control media. Different degree of inactivation and injury was observed when E coli O157: H7 strain 933 was stored in TSB (pH 5·0) containing 1 g litre⁻¹ sorbate or nitrite at 37°C. At 4°C, inactivation and injury of E coli O157: H7 cells was not observed in the medium containing sorbate or nitrite throughout the 24 h experimental period.     

Effects of cold storage and heat–acid shocks on growth and verotoxin 2 production ofEscherichia coliO157:H7

Escherichia coliO157:H7 was cold-stored (4°C) either in nutritious menstruum [buffered Brain Heart Infusion (BHI) broth] or with starvation (buffered saline) at pH 7.0 or 5.5. Cultures grown in BHI broth at 37°C for 24h served as non-cold-stored controls. After 4-weeks cold storage, bacterial cells were shocked by heat (45°C for 5min) and acid (pH 2.5 for 30min at 37°C) and subsequently moved to optimal conditions (BHI broth of pH 7.4 incubated at 37°C). The results showed: (a) both lag-phase duration and growth rate of this pathogen at 37°C significantly increased after cold-storage with starvation, but not after cold storage in the nutritious menstruum; (b) combined heat–acid shocks increased growth rates at 37°C of both previously cold-stored and non-cold-stored bacterial cells; (c) final concentrations of verotoxin produced by bacterial cells at 37°C were not affected by previous cold storage in the nutritious menstruum; (d) verotoxin production by bacterial cells at 37°C increased after cold storage with starvation, and heat–acid shocks further enhanced that production. Further research is needed to evaluate the food safety implications of these results, i.e. whether cells ofE. coliO157:H7 originating from nutrient-poor/lower-pH environments may be more harmful to humans than those from nutrient-rich/higher-pH foods.