Heat Inactivation of the Ethylene-Forming Enzyme System in Cucumbers

Heat inactivation of the ethylene-forming enzyme system (EFE) in cucumbers was biphasic and both phases followed first order kinetics. The activation energies for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFE's were 77.67 and 68.92 kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both HS and HR are as follows: enthalauv. 68.27 (HS) and 77.03 (HR) kcal/mole; free energy; 21.2 (HS) and 22.9 (HR) kcal/mole; entropy, 146.1 (HS) and 168.2 (HR) cahdeg-mole. The heat resistant EFE appears to comprise 2535% of the total EFE activity     

The heat stability and isoenzyme composition of peroxidases in Ohane grapes

Soluble and ionically bound peroxidases have been obtained from homogenized Ohane grapes. The soluble fraction contained the highest level of peroxidase activity and accounted for approximately 87% of the total enzymic activity. Plots of the percentage of heat inactivation for the grape peroxidases against time were non-linear with approximately 90% of the peroxidase activity being destroyed after 10 min at 80°C. Following heat inactivation there was no significant regeneration of enzymic activity. Using isoelectric focusing six isoperoxidases with isoelectric points ranging from approximately pI 3.5 to 9.8 were detected.     

EFFECT OF RADIO-FREQUENCY ENERGY AT 60 MHz ON FOOD ENZYME ACTIVITY

SUMMARY— The effect of radio-frequency (R-F) energy at 60 MHz on peroxidase, polyphenolase, pectinesterase, catalase and alpha-amylase activity was determined in water solutions of purified enzymes as well as in apple juice, milk and sweet potato extract. The apparatus used consisted of an R-F generator coupled to an evaporator and condenser. Temperature was kept constant at a desired level by evaporating water from the system. Results showed that while the enzymes were partially or totally inactivated by heat at 70°C. or 65°C (149°F) in the instance of milk, exposure to R-F energy at 20°C caused essentially no loss of enzyme activity. Within the limits of the experimental conditions, pH and enzyme concentration were not factors in relation to lack of effect of R-F energy on enzymes. Overall, the results indicate that per se, R-F energy at 60 MHz does not have any significant effect on the enzymes studied, aside from that caused by the heat effects of R-F energy.     

Partial Separation and Characterization of Papaya Endo- and Exo-Polygalacturonase

Exo- and endo-polygalacturonases (EC 3.2.1.40 and EC 3.2.1.15) in papayas were extracted, purified 20- and 90-fold, respectively, and characterized. Both enzymes functioned optimally at pH 4.6 and 45°C. Heat inactivation of the papaya PGases was biphasic and both phases followed first order kinetics. Decreasing the pH from 4.6 to 3.6 decreased the time required for their heat inactivation. The activation energies for the thermal inactivation at pH 3.6 and 4.6 were 85 and 92 kcal/mol, respectively, for endo-PGase (PG I) and 140 and 102 kcal/mol, respectively, for exo-PGase (PG II). The apparent molecular weight was determined by gel filtration to be 164,000 daltons for PG I and 34,000 daltons for PG II.     

THE β-N-ACETYLGLUCOSAMINIDASE ACTIVITY OF EGG WHITE. 2. Heat Inactivation of the Enzyme in Egg White and Whole Egg

SUMMARY– The kinetics of the heat inactivation of β-N-acetylglucosaminidase in egg white and whole egg at neutral pH is first order in the temperature range 58–62°C. Rate constants for enzyme inactivation by heat are reported for both egg white and whole egg. The activation energy for heat denaturation is 91 kcal/mole in egg white and 73 kcal/mole in whole egg. Reduction of enzymatic activity upon heating can be used as an indication of whether egg white or whole egg has been maintained at the time-temperature combinations approved for pasteurization by the U.S. Department of Agriculture. This test should be useful as a process control tool.     

Effects of Heat Treatments on the Ethylene Forming Enzyme System in Papayas

Heat inactivation studies were conducted on the ethylene-forming enzyme system (EFE) in papayas. Heat inactivation of the papaya EFE was biphasic and both phases followed first order kinetics. The activation energies E, for the thermal inactivation of the heat resistant (HR) and the heat susceptible (HS) EFEs were 68.3 and 51.2 Kcal/ mole, respectively. The thermodynamic constants for the heat inactivation of both EFEs were; enthalapy, 5 1.2 kcal/mole for HS and 66.7 kcal/mole for HR; free energy, 22.5 kcal/mole for HS and 23.3 kcal/mole for HR; entropy, 87.2 cal/deg-mole for HS and 137.8 call degmole for HR. The heat resistant EFE appeared to compromise about 25% of the total EFE activity. Commercial heat treatments used for quarantine treatments affected mainly the heat susceptible portion which comprised the remaining 75% of the total EFE activity.     

Thermal Stabilities of Peroxidases from Fresh Pinto Beans

Heat stabilities of crude and partially purified soluble (SPOX), ionically bound (IPOX) and total peroxidase (TPOX) from fresh pinto beans were investigated at 55–90°C. Heat inactivation of peroxidase (POX) followed first-order reaction kinetics. Each inactivation curve consisted of two linear parts: initial rapid inactivation (heat-labile) followed by slower inactivation (heat-stable). IPOX showed activation during heat treatment with a highly heat-stable isoenzyme (D₉₀=40 min) which was more heat-stable than SPOX. Activation energies for heat-stable parts of crude IPOX and SPOX were, respectively, 12.1 and 36.4 kcalmol-1 with z values 45.4 and 14.1C°. Heat stable SPOX isoenzymes (D₇₀=22.6) were obtained by 65–95% (NH₄)₂SO₄ precipitation from crude SPOX. Two POX fractions (F1 and F2) were separated from TPOX by ion-exchange chromatography.     

HEAT TREATMENT AND INACTIVATION OF TRYPSIN-CHYMOTRYPSIN INHIBITORS AND LECTINS FROM BEANS (Phaseolus vulgaris L.)

This work investigates some factors affecting the inactivation of common bean trypsin inhibitor and phytohemagglutin. Trypsin inhibitor activity was totally stable to heat treatment (30 min, 97C) in the total protein extract, albumin or globulin fraction. Heat treatment of the whole beans easily inactivated the inhibitor. Heat resistance of trypsin inhibitor was intermediate in the bean flour which received the same heat treatment. Independent of sample, the inhibitor was very stable to heat treatment at neutral and acidic pH and labile under strong alkaline conditions. Heating for 30 min in boiling water at pH 12 resulted in complete inactivation of the trypsin inhibitor. Autoclaving (121C) soaked whole beans and flour for 5 min inactivated 55% of the trypsin inhibitor activity in the soaked flour and 75% in the whole beans. After autoclaving 20 min, inactivation of trypsin inhibitor was about 65% in the flour and 80% in the whole beans. The phytohemagglutinin (lectin) activity was totally destroyed in the autoclaved beans after 5 min and in the flour after 15 min.     

Characterization of Soluble and Bound Peroxidases in Green Asparagus

Soluble and ionically bound peroxidases were extracted from green asparagus with 0.05M sodium phosphate (pH 7.0) and the same buffer containing 1.0M NaCl, respectively. The two forms of peroxidase have been purified 237 and 53 fold, respectively, through ammonium sulphate fractionation, and successive chromatography on Sephacryl S-200 and ConA Sepharose 4B columns. Eleven isoenzymes with different pI values were detected from the soluble form using isoelectric focusing and eight from the ionically bound form. The two forms of perooxidase showed a similar optimum pH range of 4.2–5.0 using three kinds of hydrogen donor with different buffers. The optimum temperature of the two peroxidase forms at pH 4.5 was around 50°C. Heat inactivation of both forms at 70° and 90°C was observed to be biphasic.     

Partial Purification and Characterization of an Acid Phosphatase from Papaya

A phosphatase in papaya was extracted, partially purified, and characterized. With p-nitrophenyl phosphate as substrate, the enzyme had a pH optimum of 6.0, which categorized it as an acid phosphatase, a temperature optimum of 37°C, and a Km of 1.0 mM. Heat inactivation of papaya acid phosphatase was biphasic, and the kinetics of both phases were first order reactions. D values at 60°, 65°, 70°C for the heat resistant phase were 21.0, 11.7, and 4.0 min, respectively. For the heat labile and heat resistant isozymes of papaya acid phosphatase, the activation energies, E_a, for thermal inactivation were 60.0 Kcal/mole and 37.8 Kcal/mole, respectively. The apparent molecular weight of the enzyme as determined by gel filtration was 120,000 daltons.     

KINETIC PARAMETERS FOR THERMAL INACTIVATION OF PLASMIN

Plasmin (EC 3.4.21.7) is the principal indigenous protease in bovine milk. Kinetic parameters for thermal degradation of plasmin were determined using a miniature continuous flow pasteurizer designed for heat treatment of small quantities of liquid. Plasmin activity was measured using a pH-stat titration, which measures the release of H ⁺ from a caseinate substrate.
Heating milk at various temperatures resulted in significant difference (P > 0.01) in residual plasmin activity and linear decrease in activity at each temperature. The calculated D-values were: 105, 90, 76.5, 62, and 47 s at 72, 78, 85, 92, and 100°C, respectively. The Z-value for plasmin inactivation was estimated to be 77.5°C, and the Arrhenius activation energy was 7.04 kcal/mole.
UHT milk containing plasmin was heated for an equivalent of 5 D inactivation of the enzyme at 100°C. After storage for 30 days at 4°C, no enzyme regeneration was observed.     

Heat inactivation of a soluble peroxidase extract from acetone powder of kohlrabi and its reactivation after heat treatment

Heat inactivation in the temperature range 70–95°C and subsequent reactivation at ambient temperature of soluble peroxidase extracts from acetone powder of kohlrabi were studied by activity measurements and isoelectric focusing in polyacrylamide gel. Between 70 and 80°C, inactivation proved not to be a simple first-order process. This showed the presence of enzyme fractions of different heat stability in the extract. At 90°C and 95°C, monophasic first-order curves were obtained which represented the inactivation of the heat stable fraction. Reactivation was most marked in its initial phase and its extent decreased with increasing temperatures of heat treatment. The progress curves of reactivation showed two or three consecutive logarithmic phases, depending on the temperature of heat treatment. This phenomenon was interpreted as resulting from selective reactivation of isoenzymes as supported by zymograms.     

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.     

THE β-N-ACETYLGLUCOSAMINIDASE ACTIVITY OF EGG WHITE. 1. Kinetics of the Reaction and Determination of the Factors Affecting the Stability of the Enzyme in Egg White

SUMMARY– Enzymatic activity of β-N-acetylglucosaminidase, which occurs naturally in chicken egg white, was characterized to establish conditions suitable for routine assay for this enzyme in egg products. A variation in enzyme content of approximately 3-fold was observed in individual fresh eggs. The enzyme has a pH optimum between 3.0 and 3.4, and a K_m of approximately 0.6 mM for the substrate p-nitrophenyl-N-acetyl-β-D-glucosaminide. Activation energy for hydrolysis of this substrate is 10.7±0.8 kcal/mole. The enzyme is stable for at least several hours at ambient temperature from pH 6.8 to approximately 8.8. Above pH 8.8, inactivation is first order with respect to time. Enzyme activity in shell eggs decreases fairly rapidly at ambient temperature; loss of activity probably results from increase in pH of egg white, which occurs normally upon loss of carbon dioxide. Eggs held at 4°C retain activity much longer.     

HEAT STABILITY OF STAPHYLOCOAGULASE MEASURED BY A CAPILLARY TUBE METHOD

Staphylocoagulase is highly heat resistant. Inactivation profiles of crude staphylocoagulase at 80, 100 and 121°C showed that total inactivation occurred after heating for 5 h,2 h and 30 min, respectively. Heat treated coagulase has the ability to reactivate when placed at 25°C for 24 hrs similar to previous observations on staphylococcal enterotoxins B and C. Staphylocoagulase could be recovered from beef broth and chicken broth before or after heating at 80°C for 5 min. Coagulase activities were measured by a quantitative capillary tube method.     

Purification and heat stability of Cox's apple pulp peroxidase isoenzymes

Three peroxidase isoenzymes, two anionic and one cationic, were isolated from extracts of apple pulp using gel filtration and ion-exchange chromatography. The homogeneity of the purified isoenzymes was established by isoelectric focusing and staining for peroxidase activity. The isoenzymes varied in their heat stability: the anionic isoenzymes were found to be more heat stable than the cationic isoenzyme. The measured enzymic activity of the isoenzymes was greatest when o -dianisidine was used as the test substrate. After heating solutions of the anionic isoenzymes at 80–100°C for 2 min, up to 80% of the original enzymic activity was observed to regenerate when the heat-treated isoenzymes were held at 30°C for 1 hr. Regeneration of enzymic activity following heat inactivation was not observed for the cationic isoenzyme.     

Thermosonication: a potential technique that influences the quality of grapefruit juice

Thermosonication (TS) is an emerging nonthermal processing technique used for the liquid food preservation and is employed to improve the quality and acceptability of grapefruit juice. In this study, fresh grapefruit juice samples were subjected to TS treatment in an ultrasonic cleaner with different processing variables, including temperature (20, 30, 40, 50 and 60 °C), frequency (28 kHz), power (70%, 420 W) and processing time (30 and 60 min) for bioactive compounds, inactivation of enzymes pectin methylesterase (PME), peroxidase (POD) and polyphenolase (PPO) and micro‐organisms (total plate count, yeasts and moulds). The micro‐organism activity was completely inactivated in the treatment (60 °C for 60 min). The TS treatment at 60 °C for 60 min exposure reduced PME, PPO and POD activity by 91%, 90% and 89%, respectively. Results indicate that the advantages of TS for grapefruit juice processing at low temperature could enhance the inactivation of enzymes and micro‐organisms and it can be used as a potential technique to obtain better results as compared to alone .     

Synergistic impact of sonication and high hydrostatic pressure on microbial and enzymatic inactivation of apple juice

The combination of innovative, non-thermal technologies for the production of safe and quality fruit juices is a recent trend in food processing. The purpose of this study was to evaluate the effects of combined treatment of ultrasound (US) and high hydrostatic pressure (HHP) on enzymes (polyphenolase, peroxidase and pectinmethylesterase), microorganisms (total plate counts, yeasts and molds) and phenolic compounds (total phenols, flavonoids and flavonols) of apple juice. Moreover, its effects on ascorbic acid, antioxidant capacity and DPPH free radical scavenging activity, color values, pH, soluble solids and titratable acidity were investigated. Fresh apple juice was treated with US (25 kHz and 70% amplitude) at 20 °C for 60 min with subsequent HHP treatment at 250, 350 and 450 MPa for 10 min at room temperature. The results revealed that the combined US-HHP450 treatment caused highest inactivation of enzymes with complete inactivation of total plate counts, yeasts and molds. It also significantly improved the phenolic compounds, ascorbic acid, antioxidant capacity, DPPH free radical scavenging activity and color values. The present results suggest that the combination of US and HHP can act as a potential hurdle to produce safe and high quality apple juice with reduced enzymes and microbial activity and improved nutrition.     

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.     

THERMOSTABLE AND THERIVIOLABILEISOFORMS IN COMMERCIAL ORANGE PEEL PECTINESTERASE1

Thermostable and thermolabile pectinesterase isoforms in commercial Valencia orange peel pectinesterase (Sigma Chemical Co., St. Louis, MO) were separated by affinity chromatography on a Heparin‐Sepharose CL‐6B column. Among the seven putative PE isoforms separated, three (P1, P2 and P3 with 70 kDa, 60 kDa and 27 kDa, respectively)‐were thermostable and four [P4, P5, P6 (35 kDa) and P7 (35 kDa)]‐were thermolabile, according to the qualitative and quantitative studies of thermal stability. The commercial PE showed 83.4% and 98.3% inactivation after heat treatment at 70C for 5 min and at 90C for 1 min, respectively. P2 was the most heat stable, with 85.5% inactivation at 70C for 5 min and 93.0% inactivation at 90C for 1 min. The thermolabile P6 and P7 could be inactivated at 70C for 5 min or at 90C for 1 min. Thermostable PE activity was 16.6% of total activity of the commercial PE based on heat treatment at 70C for 5 min, but only 1.5% based on heating at 90C for 1 min. The 90C for 1 min heat treatment might be better than the 70C for 5 min heat treatment to distinguish thermostable PE and thermolabile PE isoforms in Valencia oranges.