Microbial Safety in Radio-frequency Processing of Packaged Foods

ABSTRACT: Thermal resistance of Clostridium sporogenes (PA 3679) was determined at 115.6 °C, 118.3 °C, and 121.1 °C (240 °F, 245 °F, and 250 °F, respectively) in phosphate buffer (pH 7.0) and mashed potatoes (pH 6.3) using aluminum thermal-death-time (TDT) tubes developed at Washington State Univ. D-values were 1.8, 1.1, and 0.62 min in phosphate buffer and 2.2, 1.1, and 0.61 min in mashed potatoes at 115.6 °C, 118.3 °C, and 121.1 °C, respectively. Z-values were 12 °C and 10 °C in phosphate buffer and mashed potatoes, respectively. The thermal inactivation kinetic results were then used to validate a novel thermal process based on 27.12 MHz radio frequency (RF) energy. Trays of mashed potatoes inoculated with PA 3679 were subjected to 3 processing levels: target process (F₀∼4.3), under-target process (F₀∼2.4), and over-target process (F₀∼7.3). The microbial challenge test data showed that microbial destruction from the RF process agreed with the calculated sterilization values. This study suggests that thermal processes based on RF energy can produce safe and shelf-stable packaged foods.     

PREPARATION AND CHARACTERIZATION OF α-AMYLASE IMMOBILIZED ON COLLAGEN MEMBRANES

Crystalline pancreatic α-amylase was codispersed with hide collagen at pH 4.0 and tanned to form a membrane which degraded starch. The optimum pH for the codispersed membrane preparation was at pH 7.0 in contrast to the soluble enzyme which was as active at pH 8.0 as at pH 7.0. The immobilized enzyme responded maximally to 0.22M chloride whereas 0.02M chloride gave optimum rates for the soluble enzyme. The immobilized enzyme resisted thermal inactivation better than the soluble α-amylase. Raising the temperatures from 30 ° to 50 °C produced a 500% increase in rate for the bound enzyme. It was also demonstrated that membranes retained greater activity when stored in starch solution than in water. The effect of glutaraldehyde concentration on membrane activity was also studied.     

INFLUENCE OF SODIUM PHOSPHATE ON THE HEAT STABILITY OF BUFFALO MILK AND ITS CONCENTRATE

The influence of three different concentrations, 0.05%, 0.10% and 0.15% of monobasic sodium phosphate on the heat stability (at 130°C) and pH of buffalo milk and its 2:1 concentrate was determined. It was observed that sodium phosphate caused a considerable increase in the heat stability, determined as heat coagulation time (HCT) of concentrated buffalo milk. The optimum concentration of sodium phosphate for imparting maximum stability to the concentrate was different for different samples. However, with the addition of an appropriate concentration of sodium phosphate it was possible to manufacture evaporated milk up to 36% total solids. Depending on the HCT/pH profile, some of the samples of fluid (unconcentrated) milk were stabilized while the others were destabilized due to the addition of sodium phosphate. Addition of monobasic sodium phosphate caused a decrease in the pH of fluid milk and its concentrate.     

pH Affects the Thermal Inactivation Parameters of R-Phycoerythrin from Porphyra yezoensis

ABSTRACT: R-phycoerythrin (PE), a protein that fluoresces in the visible range, was purified from Porphyra yezoensis. PE had a molecular mass of 292 kDa and an isoelectric point of 4.1 to 4.2. Thermal inactivation parameters of PE, calculated on the basis of fluorescence loss, were determined under different pH conditions. PE was more thermostable between pH 5.0 and 8.0, and became more heat sensitive at pH 4.0 and 10.0. PE at pH 6.0 had the highest D value (12258.7 min) at 70 °C. The z values of PE increased from 4.58 °C at pH 5.0 to 9.15 °C at pH 9.0. PE could be used as a time-temperature integrator by adjusting the inactivation kinetics of PE to match those of target microorganisms in a thermal process.     

Effect of Meat Binding Formulations on Thermal Inactivation of Escherichia coli O157:H7 Internalized in Beef

ABSTRACT:  This study evaluated the effects of meat binding or restructuring formulations, including salt/phosphate, algin/calcium, Activa™RM, and Fibrimex®, with or without 0.27% (wt/wt) lactic acid, on thermal inactivation of internalized Escherichia coli O157:H7 in ground beef, serving as a model system for restructured products. Ground beef batches (700 g; approximately 5% fat) were mechanically mixed with a 5-strain composite of E. coli O157:H7 (7 log CFU/g) and then with the restructuring formulations. Product portions (30 g) were extruded into plastic test tubes (2.5 × 10 cm) and stored at 4 °C (18 h), before heating to 60 or 65 °C in a circulating water bath to simulate rare or medium-rare doneness of beef, respectively. Cooking to 60 or 65 °C reduced ( P < 0.05) bacterial counts of control samples by 1.8 and 3.2 log CFU/g, respectively. Thermal destruction at 60 °C was not different ( P > 0.05) among all treatments and the control. At 65 °C, greater ( P < 0.05) thermal inactivation of E. coli O157:H7, as compared to the control, was obtained in samples treated with lactic acid alone (reductions of 4.9 log CFU/g), whereas for all other treatments, microbial destruction (reductions of 2.2 to 4.5 log CFU/g) was comparable ( P > 0.05) to that of the control. Cooking weight losses were lower ( P < 0.05) in salt/phosphate samples (<1%) compared to other formulations and the control (7.4% to 15.9%). Findings indicated that, under the conditions examined, restructuring of beef with salt/phosphate, algin/calcium, Activa™RM, or Fibrimex® did not affect inactivation of internalized E . coli O157:H7 in undercooked (60 or 65 °C) samples, whereas inclusion of lactic acid (0.27%) in nonintact beef products enhanced pathogen destruction at 65 °C.     

Inactivation kinetics of horseradish peroxidase in organic solvents of different hydrophobicity at different water contents

The thermal stability of horseradish peroxidase suspensions was studied in three organic solvents of different hydrophobicity (dodecane, octane, and 1-octanol) at three different water contents (14.1, 55.3 and 256.2mg water g⁻¹ dry protein). In these conditions, the enzyme is much more stable than in aqueous solutions (inactivation temperatures were in the range of 125–150°C). The enzyme showed a similar stability when in the presence of organic solvents, compared to the enzyme in a solid matrix without organic solvents with the same water content. The inactivation kinetics was well described by assuming the existence of two iso-enzymes, both inactivating according to a First order model. The lowest value for the z-value of both fractions (around 15°C) was obtained at the higher water content studied. The use of solvent and water content variables should be adequate to develop time-temperature integrators to monitor thermal processes at 100–140°C.     

THE ROLE OF AMINO GROUPS IN THE BIOLOGICAL AND ANTIGENIC ACTIVITIES OF CLOSTRIDIUM PERFRINGENS TYPE A ENTEROTOXIN

Clostridium perfingens type A enterotoxin has 8 amino groups which are readily reactive with 2, 4, 6-trinitrobenzene sulfonic acid (TNBS) in 20 mM phosphate buffer, pH 6.8, and 10 amino groups which react with TNBS only after denaturation with 6.5 M guanidine · HCl ≤ 25°C. The one sulfhydryl group of enterotoxin is not reactive with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB) in the native molecule (phosphate buffer, pH 6.8), but is reactive in the presence of 0.2% sodium dodecyl sulfate at 25°C.
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Efficacy of Pressure-Assisted Thermal Processing, in Combination with Organic Acids, against Bacillus amyloliquefaciens Spores Suspended in Deionized Water and Carrot Puree

ABSTRACT:  Effect of organic acids (acetic, citric, and lactic; 100 mM, pH 5) on spore inactivation by pressure-assisted thermal processing (PATP; 700 MPa and 105 °C), high pressure processing (HPP; 700 MPa, 35 °C), and thermal processing (TP; 105 °C, 0.1 MPa) was investigated.  Bacillus amyloliquefaciens  spores were inoculated into sterile organic acid solutions to obtain a final concentration of approximately 1.3 × 10⁸ CFU/mL.  B. amyloliquefaciens  spores were inactivated to undetectable levels with or without organic acids after 3 min PATP holding time. At a shorter PATP treatment time (approximately 2 min), the inactivation was greater when spores were suspended in citric and acetic acids than in lactic acid or deionized water. Presence of organic acids during PATP resulted in 33% to 80% germination in the population of spores that survived the treatment. In contrast to PATP, neither HPP nor TP, for up to 5 min holding time with or without addition of organic acids, was sporicidal. In a separate set of experiments, carrot puree was tested, as a low-acid food matrix, to study spore recovery during extended storage following PATP. Results showed that organic acids were effective in inhibiting spore recovery in treated carrot puree during extended storage (up to 28 d) at 32 °C. In conclusion, addition of some organic acids provided significant lethality enhancement ( P  < 0.05) during PATP treatments and suppressed spore recovery in the treated carrot puree.     

Formulation and shelf-life of a bottled pawpaw juice beverage

A simple procedure was developed for production of bottled pawpaw beverage juice by peeling and macerating peeled tissue in 25% water, straining through a 0.8-mm sieve, adjustment of juice pH with citric acid and flavour adjustment with sucrose. Fresh juice was optimized for acceptability at pH 3.9 and 10% (w/w) sucrose. Heating for 6 min at 72.2°C was required to achieve commercial pasteurization. Samples of juice were prepared with no preservative, and containing sodium benzoate (125mg/100ml), sodium metabisulphite (50mg/100ml) and sodium metabisulphite/sodium benzoate combination (25mg and 60mg/100ml) for trials in which acceptability, pH, specific gravity, brix, total acidity, vitamin C and biomass concentrations were measured over 90 weeks storage at 10°C and 30.2°C. Sodium benzoate alone extended the shelf-life at 30°C up to 80 weeks but the other preservatives were not effective after 20 weeks. The control juice was already deteriorating by 10 weeks at 30°C. At 10°C all preserved samples were stable up to 80 weeks, although the control deteriorated rapidly after 20 weeks.     

Inactivation of Pectin Methyl Esterase in Orange Juice by Pulsed Electric Fields

ABSTRACT: Pulsed electric fields (PEF) treatments were applied to nonpasteurized orange juice using a bench top PEF system to study effects of PEF on the activity of pectin methyl esterase (PME). Effects of electric strength on PME activity at a constant water bath temperature were studied using electric field strengths up to 35 kV/cm at 30 °C. Increase of electric field strength caused a significant inactivation of PME with increase in orange juice temperature ( p < 0.05). A thermal inactivation study showed that heating of orange juice at the same temperature as orange juice during PEF treatment was not effective as PEF treatment in inactivating PME. Effects of electric field strength at different water bath temperatures were studied using electric field strengths up to 25 kV/cm and water bath temperatures of 10–50 °C. Higher electric field strengths at higher water bath temperature were the more effective to inactivate PME. A combination of PEF treatment at 25 kV/cm and a water bath temperature of 50 °C caused 90% inactivation of PME.     

Reversed Micellar Extraction of Hen Egg Lysozyme

Egg white was diluted to 10 times its original volume with 50 mM phosphate buffer (pH 9.2) containing 0.1 M potassium chloride. The aqueous solution was mixed with an equal volume of isooctane containing 50 mM bis-(2-ethylhexyl) sodium sulfosuccinate at 10°C for 50 min. After extraction, the organic phase containing lysozyme was separated from the aqueous phase and mixed with an equal volume of 50 mM phosphate buffer (pH 11.8) containing 1M potassium chloride. Backward extraction was then performed at 30°C for 45 min. The procedures recovered 90% lysozyme from the eggwhite. The specific activity of the extract was near 73,000 units/mg.     

Effect of pH on Inactivation of Escherichia coli K12 by Sonication, Manosonication, Thermosonication, and Manothermosonication

ABSTRACT:  The effect of pH on inactivation of Escherichia coli K12 by sonication at 100 kPa/40 °C, manosonication (MS) at 400 kPa/40 °C, thermosonication (TS) at 100 kPa/61 °C, and manothermosonication (MTS) at 400 kPa/61 °C at acoustic energy density of 3 W/mL and 6 W/mL was investigated. Five linear and nonlinear kinetic models were used to examine the inactivation kinetics. At all pH levels, the inactivation rates of E. coli K12 in a buffer by TS and MTS were significantly higher than those by sonication and MS. A 5 log reduction of E. coli K12 population by TS and MTS was achieved in 0.5 and 0.25 min, respectively. With an initial count of 10⁸ CFU/mL, no colonies were detected at pH 3 after a 0.25-min MTS treatment. The lethal effect of MTS was enhanced at low pH (pHs 3 and 4), whereas at nonlethal temperature of 40 °C, no increased killing was observed. Regardless of pH, the treatment by MTS, TS, and MS exhibited a rapid initial reduction followed by tailing-off on the inactivation curves. The biphasic linear, log-logistic, and modified Gompertz kinetic models allowed better fitting of the inactivation data for MTS, TS, and MS treatments than the 1st-order and Weibull models. The survival counts of sonication-treated E. coli K12 at all pH levels fitted well to a 1st-order kinetic model.     

Water activity of bacterial suspension media unable to account for the baroprotective effect of solute concentration on the inactivation of Listeria monocytogenes by high hydrostatic pressure

Inactivation of Listeria monocytogenes (10(8) CFU/ml) by high hydrostatic pressure (HHP) from 400 to 600 MPa at 25 degrees C for 10 min was investigated with various concentrations of sodium chloride, sucrose, and sodium phosphate buffer solutions. Sodium chloride significantly inhibited HHP-induced inactivation of L. monocytogenes at concentrations higher than 2.6 M. A low concentration of sodium chloride within 1.7 M had no effect on HHP-induced inactivation. Almost complete inactivation at relatively low sodium chloride concentration solution was observed with treatments above 500 MPa. Sucrose also significantly inhibited HHP-induced inactivation of L. monocytogenes when greater than 1.2 M sucrose solutions were used. HHP-treatment at 400 MPa reduced the number of L. monocytogenes in 1.2 M, 1.5 M, and 1.8 M sucrose solutions by 4.8, 2.0, and 0.7 log cycles, respectively. Higher pressure did not yield significant reductions. Sodium phosphate buffer significantly inhibited HHP-induced inactivation of L. monocytogenes. In particular, 1 M phosphate buffer completely inhibited HHP-induced inactivation even at 600 MPa. HHP-treatment at 400 MPa reduced the number of L. monocytogenes in 0.1 M, 0.25 M, and 0.5 M phosphate buffer solutions by 5.6, 4.1, and 3.2 log cycles, respectively. The effect of HHP-induced inactivation of L. monocytogenes in the three kinds of solution was evaluated by adjusting water activity (a(w)). However, the baroprotective effect differed depending on the kind of solute even at the same a(w). This result showed no consistent correlation between a(w) and solute concentration in terms of the baroprotective effect. As an alternative approach, saturation of suspension solution was used for evaluating the effect of HHP-induced inactivation of L. monocytogenes. As the saturation of suspension media increased, the effect of HHP-induced inactivation of L. monocytogenes decreased regardless of the kinds of solute. The saturation of solution would be an alternative parameter of inhibition in terms of HHP-induced inactivation of bacteria.     

INSTABILITY OF SODIUM NITRITE IN A CHEMICALLY DEFINED MICROBIOLOGICAL MEDIUM

Mixtures of sodium nitrite, amino acids and ascorbic acid at pH 6.3 or 7.2 were filter sterilized or heated for various times at 121°C. Samples were analyzed for nitrite concentration immediately after treatment and after storage at 37 or 43°C. Heating the complete medium for 15 min at 121°C reduced the nitrite concentration by 30–50% independent of the initial nitrite concentration. Storage of complete filter sterilized medium at 43°C for 18–24 hr resulted in 50–65% loss of nitrite while in heat sterilized medium the loss was as great as 90%. None of the 19 amino acids stored individually with sodium nitrite at 37°C for up to 4 hr affected the nitrite concentration, whereas ascorbic acid resulted in total disappearance of nitrite. During heating at 121°C of the 19 amino acids only cystine resulted in any significant nitrite loss after 15 min of treatment while ascorbic acid effected total nitrite disappearance after 5 min. The defined medium containing nitrite demonstrated inhibitory activity against seven strains of Clostridium perfringens.     

Flow Properties of Chickpea Proteins

Flow properties of aqueous chickpea protein dispersions were investigated. The dispersions had Newtonian flow behavior at concentrations up to 4%. Flow behavior became progressively less Newtonian as concentration increased above 4%. The apparent viscosity of the dispersions was pH and concentration dependent, being higher at the protein's most soluble pHs (pH 2 and 9) and lower at the isoelectric point (pH 4–5). Within the investigated temperatures (15, 25, 35 and 55°C), power law constants were unchanged up to 35°C but the flow behavior became non-Newtonian at 55°C. Denaturation by urea and sodium dodecyl sulphate (SDS) increased the consistency index (m), casson yield stress and apparent viscosities, and the flow became more pseudoplastic with a decrease in the flow index (n).     

Effect of Ice Storage on the Physicochemical and Dynamic Viscoelastic Properties of Ribbonfish (Trichiurus spp) Meat

ABSTRACT: Changes in physicochemical and dynamic viscoelastic properties of ribbonfish ( Trichiurus spp) meat during different periods of ice storage were investigated. The differential scanning calorimetry profile of fresh ribbonfish meat revealed transitions at 33.17 °C, 48.85 °C, and 60.96 °C, indicating denaturation temperature of different protein fractions. The effect of cornstarch or tapioca starch at 9% level on the viscoelastic properties of ribbonfish meat stored in ice for different periods was also evaluated. Total volatile basic nitrogen (TVBN) increased significantly ( P < 0.05) during ice storage for 24 d. However, the myosin heavy chain concentration was unaltered during the ice storage period, as revealed by sodium dodecyl sulphate-polyacrylamide gel electrophore-sis (SDS-PAGE) pattern. A significant ( P < 0.05) decrease in protein solubility (in phosphate buffer 50 m M , pH 7.5, containing 1 M NaCl), calcium-activated adenosine triphosphatase (ATPase) activity, and an increase in reduced viscosity at a protein concentration of 5 mg/mL was observed after 10 d of ice storage indicating protein denaturation and aggregation. The addition of tapioca and cornstarch enhanced storage modulus values of fresh ribbonfish meat. The gelatinization temperature of tapioca starch solution was found to be in the range of 60 °C to 65 °C and for cornstarch 67 °C to 70 °C, as revealed by the differential scanning calorimetry (DSC) profile and dynamic rheological testing. The viscoelastic properties of ribbonfish meat was altered significantly ( P < 0.05), both due to the addition of starch and ice storage period as revealed by frequency sweep of prepared gels.     

Prediction of toxin production by Clostridium botulinum in pasteurized pork slurry

A model pork slurry system was used to study factors controlling the growth of Clostridium botulinum types A & B (Roberts, Gibson & Robinson, 1981a,b). The following factors were studied in combination: sodium chloride (2.5, 3.5, 4.5% w/v on water); sodium nitrite (100, 200, 300 μg/g); sodium nitrate (0, 500 μg/g); sodium isoascorbate (0, 1000 μg/g); polyphosphate (Curaphos 700, 0, 0.3% w/v); heat treatment (none, 8°C/7 min, 80°C/7 min + 70°C/1 hr); at two pH levels and stored at: 15, 17.5, 20 or 35°C.
Analyses of results yielded a statistical model providing two formulae (for 'low' and 'high' pH slurries) which estimate the probability of toxin production in the pork slurry system within the limits defined above.     

Effects of pH and temperature on inactivation of Salmonella typhimurium DT104 in liquid whole egg by pulsed electric fields

Pulsed electric field (PEF) exposes a fluid or semi-fluid product to short pulses of high-energy electricity, which can inactivate microorganisms. The efficacy of PEF treatment for pasteurisation of liquid eggs may be a function of processing temperature. In this study, effects of PEF, temperature, pH and PEF with mild heat (PEF + heat) on the inactivation of Salmonella typhimurium DT104 cells in liquid whole egg (LWE) were investigated. Cells of S. typhimurium were inoculated into LWE pH adjusted to 6.6, 7.2 or 8.2 at 15, 25, 30 and 40 °C. The PEF field strength, pulse duration and total treatment time were 25 kV cm⁻¹, 2.1 μs and 250 μs respectively. Cells of S. typhimurium in LWE at pH 7.2 were reduced by 2.1 logs at 40 °C and 1.8 logs at 30 °C. The PEF inactivation of S. typhimurium cells at 15 or 25 °C was pH dependent. Heat treatment at 55 °C for 3.5 min or PEF treatment at 20 °C resulted in c. 1-log reduction of S. typhimurium cells. Combination of PEF + 55 °C achieved 3-log reduction of S. typhimurium cells and was comparable to the inactivation by the heat treatment at 60 °C for 3.5 min. With further development, PEF + heat treatment may have an advantage over high-temperature treatment for pasteurisation of liquid eggs.     

IDENTIFICATION AND CHARACTERIZATION OF SOME OXIDIZING ENZYMES OF THE MC FARLIN CRANBERRY

SUMMARY– Enzyme extracts were prepared from acetone powders with and without phenol-binding agents such as polyethylene glycol (PEG) and polyvinylpyrrolidone (PVP) and buffered PVP. The acetone-PVP combination was found most effective in reducing the polyphenolic content of the enzyme extract. Highest specific activity was obtained by using a buffered PVP extract. The pH optimum of cranberry peroxidase activity was 6.0. Heat inactivation of cranberry peroxidase was determined to follow first order kinetics. There was 90% destruction at 70, 80, and 90°C requiring 9.40, 1.60, and 0.47 min of heat treatment, respectively. Activation energy for the thermal inactivation of cranberry peroxidase was observed to be 37.2 kcal/mole. Guaicol, o-phenylene diamine (OPDA), and pyrogallol were tested for their sensitivity to cranberry peroxidase with OPDA determined as most sensitive. The pH optimum for catalse activity was found to range from 7.5 to 9.2. Kinetics for the heat inactivation of cranberry catalase was observed not to be of the first order nor zero order. Approximately 50% of the catalase activity was inactivated after heating for 17, 1.8, and 0.6 min at temperatures of 50, 60, and 70°C, respectively. The pH optimum for cranberry polyphenolase activity was determined to be 7.0. Heat inactivation of cranberry poly-phenolase was found to follow first order kinetics. There was 90% destruction at 50, 60, and 70°C requiring 15.85, 7.05, and 1.37 min of heat treatment, respectively. The activation energy for the inactivation of cranberry polyphenolase was observed to be 27.7 kcal/mole.     

The influence of water activity on thermal stability of horseradish peroxidase

The thermal stability of horseradish peroxidase in the solid state was studied as a function of water activity, from 0.11 to 0.88. At all activities the enzyme was found to be much more stable in the solid state than in solution. Inactivation temperatures were in the range of 140–160°C. Inactivation curves show a biphasic behaviour which can be described by a model assuming two fractions (heat labile and heat stable) with independent first order inactivation kinetics. The labile fraction represents approximately 30% of the total activity. The z-value for both stable and labile fractions depends on water activity (moisture content) and has a maximum at a_w= 0.76 (44.4°C and 43.8°C, respectively).