Migration of antimony from PET trays into food simulant and food: determination of Arrhenius parameters and comparison of predicted and measured migration data

Migration experiments with small sheets cut out from ovenable PET trays were performed in two-sided contact with 3% acetic acid as food simulant at various temperatures. The fraction of diffusible antimony (Sb) was estimated to be 62% in the PET sample under study. Apparent diffusion coefficients of Sb in PET trays were determined experimentally. Measurement of migration between 20 and 150°C yielded a linear Arrhenius plot over a wide temperature range from which the activation energy (E _a) of 188?±?36?kJ?mol^?1 and the pre-exponential factor (D ₀) of 3.6?×?10¹⁴?cm²?s^?1 were determined for diffusing Sb species. E _a was similar to previously reported values for PET bottles obtained with a different experimental approach. E _a and D ₀ were applied as model parameters in migration modelling software for predicting the Sb transfer in real food. Ready meals intended for preparation in a baking oven were heated in the PET trays under study and the actual Sb migration into the food phase was measured by isotope dilution ICP-MS. It was shown that the predictive modelling reproduces correctly experimental data.     

Effect of Oxygen on Thermal Degradation of 5-Methyl-5,6,7,8-Tetrahydrofolic Acid

Previous studies of thermal degradation of folic acid have not given consistent rate expressions or activation energies. The present study employed a model system which eliminated oxygen mass transfer limitations to examine degradation as a result of heating. A pseudo first-order reaction rate constant (k_365.K) and an activation energy (E_a) for thermal degradation due to an oxidative mechanism were estimated to be 0.154 ± 0.044 min^?1 and 16.3 kcal/mol, respectively. In the presence of N₂, these parameters were estimated to be 0.094 ± 0.009 min^?1 and 23.3 kcal/mol, respectively. While elimination of oxygen will not ensure folic acid retention, the overall degradation rate will be reduced significantly.     

Determination of some biochemical properties of polyphenol oxidase from Emir grape (Vitis vinifera L. cv. Emir)

Polyphenol oxidase (PPO) was extracted from Emir grapes grown in Turkey and its characteristics in terms of pH and temperature optima, thermal inactivation, kinetic parameters and potency of some PPO inhibitors were studied. The optimum pH and temperature for grape PPO were found to be 4.2 and 25 °C respectively using catechol as substrate. K_m and V_max values were found to be 25.1 ± 2.72 mmol L⁻¹ and 0.925 ± 0.04 OD₄₁₀ min⁻¹ respectively. Of the inhibitors tested, the most potent was sodium metabisulfite, followed by ascorbic acid. The thermal inactivation curve was biphasic. Activation energy (E_a) and Z values were calculated as 251.4 kJ mol⁻¹ (r² = 0.996) and 8.92 °C (r² = 0.993) respectively. Copyright © 2006 Society of Chemical Industry     

Characterization of Sultaniye grape (Vitis vinifera L. cv. Sultana) polyphenol oxidase

Polyphenol oxidase (PPO) was extracted from Sultaniye grapes grown in Turkey, and its characteristics in terms of pH and temperature optima, thermal inactivation, kinetic parameters and potency of some PPO inhibitors were studied. Optimum pH and temperature for grape PPO were found to be 3.4 and 30 °C, using catechol as substrate. K_m and V_max values were found to be 44.5 ± 5.47 mm and 0.695 ± 0.0353 OD₄₁₀ min^?1, respectively. Four inhibitors were tested in this study and the most potent inhibitor was sodium metabisulphite, followed by ascorbic acid. From the thermal inactivation studies in the range of 65–80 °C, the half‐life values of the enzyme ranged between 2.6 and 49.5 min. Activation energy (E_a) and Z values were calculated to be 208.5 kJ mol^?1 (r² = 0.9544) and 10.95 °C (r² = 0.9517), respectively.     

Equilibration of Solutes in Nonfermenting, Brined Pickling Cucumbers

The equilibration of solutes between whole cucumbers and the brine in which they were held was found to be consistent with a diffusion-controlled first-order rate process. First-order rate coefficients for attainment of equilibrium (K_D) for sugar and malic acid (initially in cucumbers) and NaCl and lactic, tartaric, acetic and formic acids (initially in brine) varied up to threefold among four cucumber lots. However, the ratios of K_D values among solutes were not significantly different (P>0.05). K_D values increased as cucumber size decreased. Peeling increased K_D values 3.7- to 11.1-fold. Temperature dependency was greater for solute movement out of [apparent activation energies (E_a) of 6.5 and 6.3 kcal/mole for malic acid and sugar] than into (apparent E_a of 4.5 and 4.2 kcal/mole for NaCl and lactic acid) cucumbers. The equilibration-prediction model used may be helpful in studying rate limiting factors in the fermentation of brined vegetables and in other food preservation processes where solute movement is important.     

THE EFFECT OF pH ON RAPESEED GLOBULIN (CRUCIFERIN) BINDING TO ANILINONAPHTHALENE-8-SULFONATE

The fluorescence emission intensity from rapeseed globulin (cruciferin) increased in the presence of anilinonaphthalene-8-sulfonate (ANS) at pH 2.0 but not at pH 10. Fluorescence titration studies showed that at pH 7 cruciferin binds 22 (±0.6) moles of ANS per mole of protein with an average dissociation constant (K_d) of 1.9 (±0.1) × 10^?5 M. At pH 2.0 the number of ligand binding sites (n) decreased to 14 (±0.2) moles of ANS bound per mole of cruciferin. However, the ANS binding affinity increased by about five times (K_d= 3.6 (±1.1) × 10^?6 M). The fluorescence emission spectrum maxima (Λ_max) for the cruciferin-ANS complex showed a blue shift at pH 2 when compared to Λ_max values at pH 7–10. These results are consistent with a loss of the quaternary and tertiary structures of cruciferin and the exposure of surface hydrophobic ANS binding sites at low pH. Cruciferin-ANS binding parameters at pH 10 were not significantly different from values at pH 7; n = 22 and K_d= 2.7 (±0.2) × 10^?5 M. Based on these ANS fluorescence measurements cruciferin is stable under alkaline conditions.     

Effect of Octenylsuccinylation on Rheological Properties of Corn Starch Pastes

Rheological properties of corn starch octenylsuccinate (OSA starch) pastes (5%, w/w), at different 1‐octenylsuccinic anhydride (OSA) contents (0, 1.0, 1.5, 2.0 and 2.5%, w/w) were evaluated in steady and dynamic shear. The OSA starch pastes had high shear‐thinning behaviors and their flow behaviors were described by power law, Casson, and Herschel‐Bulkley models. Magnitudes of consistency index (K, K_h) and yield stress (σ_oc, σ_h) increased with the increase in OSA content and the decrease in temperature. Over the temperature range of 10–50°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 10.7–13.9 kJ/mol) of OSA starches were lower than that (E_a = 15.9 kJ/mol) of native starch. Dynamic frequency sweep test showed that both storage modulus (G′) and loss modulus (G′′) of OSA starch pastes increased with the increase in OSA content. Dynamic (η^*) and steady shear (η_a) viscosities of OSA starch pastes at various OSA contents did not follow the Cox‐Merz superposition rule.     

Kinetics of Thermal Inactivation of Peroxidase and Color Degradation of African Cowpea (Vigna unguiculata) Leaves

Cowpea leaves form an important part of the diet for many Kenyans, and they are normally consumed after a lengthy cooking process leading to the inactivation of peroxidase (POD) that could be used as an indicator for the potential shelf life of the vegetables. However, color degradation can simultaneously occur, leading to poor consumer acceptance of the product. The kinetics of POD in situ thermal (for thermal treatments in the range of 75 to 100 °C/120 min) inactivation showed a biphasic first‐order model, with Arrhenius temperature dependence of the rate constant. The kinetic parameters using a reference temperature (T_ref) of 80 °C were determined for both the heat‐labile phase (k_ref = 11.52 ± 0.95 × 10^?2 min^?1 and E_a of 109.67 ± 6.20 kJ/mol) and the heat‐stable isoenzyme fraction (k_ref = 0.29 ± 0.07 × 10^?2 min^?1 and E_a of 256.93 ± 15.27 kJ/mol). Color degradation (L*, a*, and b* value) during thermal treatment was investigated, in particular as the “a*” value (the value of green color). Thermal degradation (thermal treatments between 55 and 80 °C per 90 min) of the green color of the leaves followed a fractional conversion model and the temperature dependence of the inactivation rate constant can be described using the Arrhenius law. The kinetic parameters using a reference temperature (T_refC = 70 °C) were determined as k_refC = 13.53 ± 0.01 × 10^?2 min^?1 and E_aC = 88.78 ± 3.21 kJ/mol. The results indicate that severe inactivation of POD (as an indicator for improved shelf life of the cooked vegetables) is accompanied by severe color degradation and that conventional cooking methods (typically 10 min/100 °C) lead to a high residual POD activity suggesting a limited shelf life of the cooked vegetables.     

Control of Enzymatic Browning in Processed Mushrooms (Agaricus bisporus)

Control of polyphenol oxidase (E.C. 1.14.18) activity by the use of citric acid was investigated. The enzyme was inactivated at pH 4.0 and was stable to 10 min exposures at 25°C in the pH range 4.0–8.0. At pH 6.5 the enzyme was active at 45°C but not at 70°C and thermal inactivation followed pseudo first-order kientics. At pH 6.5 the activation energy (E_a) for enzyme inactivation was 41.1 Kcal/mole while at pH 3.5 two rate constants and hence two values for E_a were observed. Between 0–5 min E_a for inactivation of polyphenol oxidase was 8.7 Kcal/mole and >5 min Ea was 21.8 Kcal/mole.     

PURIFICATION AND SOME PROPERTIES OF LINAMARASE FROM CASSAVA (Manihot esculenta) CORTEX

The enzyme linamarase (E. C. 3.2.1.21) has been purified from cassava cortex (Manihot caculenta) by techniques involving acetone precipitation, ammonium sulfate fractionation, gel filtration and ion-exchange chromatography. Two peaks of linamarase activity (A & B) were eluted by linear gradient on DEAE-Sephadex column. Both forms of the enzyme were found to catalyze similar reactions, however, at different rates. Double reciprocal plots from initial velocity data gave K_m of 1.47 mM & 1.44 mM for linamarase A & B, respectively, with linamarin as substrate. The K_m values with the artificial substrate para-nitrophenyl glucoside (PNP-G) were 0.48 mM, Both enzyme forms exhibited maximal activity at pH 6.0 and 30°C. Arrhenius plots gave activation energy (E_a) as 49 KJ/mole (11.72 Kcal mole^?1) and 36.5 KJ/mole (8.72 Kcal mole^?1) for linamarase A & B, respectively. Analysis of cyanide levels in cassava and its products with the crude enzyme showed the leaves to contain high levels of the toxic factor.     

Kinetic Parameter Estimation in Conduction Heating Foods Subjected to Dynamic Thermal Treatments

The purpose of this work was to develop a means for determining product and process specific thermal kinetic parameters of constituents in foods that do not heat uniformly. The concept of the method of Paired Equivalent Isothermal Exposures (PEIE) was developed for such products. The ability of the PEIE to define Arrhenius parameters from simulated retort experiments was demonstrated. The PEIE was applied to survival data from retort experiments of canned pea puree inoculated with Bacillus stearothermophilus spores (NCA 1518). Mean activation energy and reaction rate constant (at 121.1°C) of the spores in retort processed canned pea puree were E_a= 250 (± 15) kJ/mol and k_121.1°C= 0.26 (0.23 < k_121.1°C <0.30) min^?1, respectively.     

Desulphiting dried apricots by exposure to hot air flow

Sulphited dried apricots were exposed to hot air flows at 40, 50 and 60 °C and the removal of SO₂ was investigated as their moisture content fell from an initial value of 193.2 g kg^?1 to a final value of 80–90 g kg^?1. A first‐order kinetic model was found for the removal of SO₂ between 40 and 60 °C. Temperature quotients (Q₁₀) for the removal of SO₂ were 2.84 between 40 and 50 °C and 4.93 between 50 and 60 °C; the activation energy (E_a) was 114.40 kJ mol^?1 between 40 and 60 °C. Analysis of the kinetic data also suggested a first‐order reaction for non‐enzymatic browning, with Q₁₀ values of 2.34 between 40 and 50 °C and 5.36 between 50 and 60 °C and an E_a value of 109.36 kJ mol^?1 between 40 and 60 °C. Exposure of dried apricots to a 60 °C air flow resulted in a rate constant for brown pigment formation that was 12 and 5 times higher than those at 40 and 50 °C respectively. © 2002 Society of Chemical Industry     

Kinetic Characterization and Thermal Inactivation of Peroxidase in Aqueous Extracts from Sweet Corn and Waxy Corn

The objective of this study was to evaluate the activity, kinetic behavior, and thermal inactivation kinetics of peroxidase (POD) in aqueous extracts from two kinds of milk ripe stage corn, sweet corn and waxy corn. Optimum activities using guaiacol as the hydrogen donor were obtained for sweet corn at pH 4.8 and for waxy corn at pH 6.0. The kinetics of POD showed characteristics which were dependent upon the concentrations of guaiacol and H₂O₂. The guaiacol K _m values for sweet corn POD and waxy corn POD were 11.01 and 23.01 mM, respectively, whereas the H₂O₂ K _m values for sweet corn POD and waxy corn POD were 2.85 and 0.33 mM, respectively. Thermal treatment of enzymatic aqueous extracts was carried out at different time–temperature combinations in the range of 0–25 min and 60–85 °C. Arrhenius plot determination and calculated thermodynamic parameters suggested that the inactivation of POD followed first-order reaction kinetics, and the activation energy (E _a) for inactivation of sweet corn POD (114.36 kJ/mol) was slightly lower compared with waxy corn POD (119.72 kJ/mol). There were several notable similarities between the inactivation kinetics in the two corn cultivars.     

Biochemical characteristics and thermal inhibition kinetics of polyphenol oxidase extracted from Thompson seedless grape

Polyphenol oxidase (PPO) was isolated from Thompson seedless grape (Vitis vinifera ‘Thompson Seedless’), and its biochemical characteristics were studied. The PPO showed activity to catechol and D, L-DOPA, but not towards monophenol l-Tyrosine, diphenols guaiacol and caffeic acid, and triphenols pyrogallic acid and gallic acid. Apparent Michaelis–Menten constant (K _m) and maximum velocity of the reaction (V _max) values were 45.0 ± 0.05 mM and 500.0 ± 15.3 OD_400 nm/min for catechol, and 34.6 ± 0.03 mM and 384.6 ± 11.7 OD_478 nm/min for D, L-DOPA, respectively. The obtained similar specificity values of V _max/K _m ratio of catechol and D, L-DOPA indicated their similar affinity to Thompson seedless PPO. The most effective inhibitor was l-cysteine, followed in decreasing order by ascorbic acid, sodium metabisulfite, EDTA, NaCl, and citric acid. It was discovered that metal ions of Mg²⁺ and Cu²⁺ increased, while Zn²⁺ and K⁺ reduced the PPO activity. Sugars showed inhibition on the PPO activity, with higher effect by sucrose and lower effect by fructose and glucose. Optimum pH and temperature for grape PPO activity were 6.0 and 25 °C with 10 mM catechol as substrate. The enzyme was heat stable between 10 and 25 °C, but showed significant activity loss at temperatures higher than 40 °C and completely inactivation at 70 °C for 10 min. Thermal inactivation of PPO showed a first-order kinetic with an activation energy (E _a) of 146.1 ± 10.8 kJ/mol at pH 6.0.     

Kinetics of Quality Changes of Shrimp (<Emphasis Type="Italic">Litopenaeus setiferus</Emphasis>) During Pasteurization

Effect of cooking between 1 and 80 min at 60 to 100 °C on several quality attributes of whole peeled shrimp (Litopenaeus setiferus) (80–90 counts/kg) was studied using an isothermal heating method. Cook loss, area shrinkage, and hardness of shrimp increased with increasing heating time and temperature, following a fractional first-order kinetic model with activation energies (E _a ) of 71.0, 53.3, and 29.9 kJ/mol, respectively. Cook loss, area shrinkage, and hardness were positively correlated. The toughness of shrimp muscle increased in the initial period of heating, then decreased in the later period during the treatments. The overall color change (ΔE) increased with increasing treatment time and temperature, and followed a zero kinetic model with an E _a of 37.2 kJ/mol. The kinetic parameters obtained from this study can be applied toward understanding and predicting shrimp-quality changes during pasteurization treatments, and further provides insight into the pasteurization conditions required to achieve safe and high-quality shrimp products and potentially other crustacean shellfish and seafood products.     

Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that (E_a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E_a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage (G′) and loss (G′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G′ and G′′ increased with the increase in gum concentration. Dynamic rheological data of ln (G′, G′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G′ greater than G′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.     

Develop Mechanistic Models of Transition Periods between Lag/Exponential and Exponential/Stationary Phase

A continuing goal in predictive microbiology is models directly based on physiological behavior. Buchanan et al.¹ hypothesized that (1) the curvilinear lag/exponential transition represents the variability of cells in the adjustment (t_a) and metabolic (t_m) periods, and (2) the exponential/stationary transition is determined by limiting nutrient diffusion rates. Nutritional shift trials were conducted to estimate E.coli K-12 growth. Lactase production time suggest that lactase gene translation occurs after completion of lag phase. Agitation rates and inoculum sizes both influenced the shape of the exponential/stationary phase transition. Monte Carlo simulations allowed the generation of sigmoidal growth curves while considering physiological events.     

Biochemical and Structural Changes of Taro (Colocasia esculenta) Tubers During Simple Thermal Treatments (Low Temperature) or in Combination with Chemicals

The present study set out to study the structural and biochemical modification of taro (Colocasia esculenta) grown in Cameroon, through simple heating or in association with chemicals. Both techniques are known to inactivate the reactions of polyphenol oxidase. The textural analysis was performed on tubers heated in water, 0.5% NaCl and 1% NaCl solution at various times from 0 to 105?min. The result showed optimum pH and temperature for taro polyphenol oxidase (PPO) activity at pH?6.0 and t?=?40?°C with 10?mM catechol in 0.1?M phosphate buffer as substrate. K _m and V _max values were about 7.317?±?0.012?mM and 0.148?±?0.0003 OD_{430 nm}/minute. Seven inhibitors were tested in this study, and the most effective inhibitors were found to be NaCl, CaCl2 and KCl. Kinetic studies showed that the thermal inactivation of taro PPO followed first-order kinetics, with an activation energy of E _a?=?422.79?±?0.52?kJ/mol. The textural modification of taro tubers during heating follows the kinetic of the fractional model. It was noticed that the activation energy increased with the concentration of NaCl.     

Lysyl oxidase from jumbo squid (Dosidicus gigas) muscle: purification and partial characterization

Lysyl oxidase (LOX; E.C.1.4.3.13) was purified from jumbo squid muscle (Dosidicus gigas) with 1900‐fold and yield 1.9%, and characterized for the first time. The purification procedure consisted of fractionation with urea and a combination of size‐exclusion and anion‐exchange chromatography. The enzyme had a molecular weight of 32 kDa, as estimated by SDS‐PAGE. Using a specific LOX substrate (1,5‐diaminopentane), its optimum activity was determined at pH 8.2 and 65 °C. Activation energy (E_a) of the enzyme was 69.94 kJ K^?1 mol^?1. The enzyme was strongly inhibited by β‐aminopropionitrile fumarate (BAPN), a specific LOX inhibitor. Moreover, purified LOX was able to work at different temperatures (20–90 °C) at pH 8.2. Although further research is needed, the results from this work suggest that based on LOX activity, this enzyme may be of practical use in preventing textural changes in jumbo squid during storage or processing.     

Establishment of quality predictive models for bighead carp (Aristichthys nobilis) fillets during storage at different temperatures

Quality predictive models were developed to predict the freshness of bighead carp (Aristichthys nobilis) fillets during storage at different temperatures. Quality indices [sensory score, total volatile base nitrogen (TVB‐N), total aerobic counts (TAC) and K value] at ?3, 0, 3, 9 and 15 °C were estimated and kinetically modelled by the Arrhenius equation. The activation energy (E_A) of sensory score, TVB‐N, TAC and K value was 78.17, 75.93, 106.53 and 76.21 kJ mol^?1, and the corresponding rate constants (k₀) were 1.16 × 10¹⁵, 2.60 × 10¹⁴, 4.05 × 10¹⁹ and 1.36 × 10¹⁵. The high regression coefficients (R² > 0.87) indicated the acceptability of the zero‐order reaction for sensory score, TVB‐N, TAC and K value. Relative errors between predicted and observed freshness indicators values of sensory score, TVB‐N, TAC and K value were all below 10% except the values at 6th day of K value, 3rd day and 9th day of TVB‐N. These results indicated that the models based on sensory score, TVB‐N, TAC and K value could effectively predict the freshness indicators of bighead carp fillets at the range of ?3 to 15 °C.