Pulse Duration and Efficiency of Soft Cellular Tissue Disintegration by Pulsed Electric Fields

The effect of pulse duration on efficiency of disintegration of apple tissue by pulsed electric fields (PEF) was studied. The samples (26-mm diameter, 10-mm height) were treated by PEF at electric field strength E between 100 and 400 V/cm, pulse duration t _i of 10, 100, 1,000 μs, inter-pulse duration Δt of 100 μs and different number of pulses n. Both the degree and the time evolution of tissue damage were quantified by electrical conductivity disintegration index Z and characteristic damage time τ, respectively. The samples exposed to the same PEF treatment time nt _i showed noticeably higher disintegration efficiency for larger pulse duration. The synergism of PEF and thermal treatment with temperature T (20–50 °C) was demonstrated. The Arrhenius dependence of τ(T) for PEF treatment at E = 100 V/cm gave the decreasing activation energy W as a function of t _i, (Q ≈ 164 kJ/mol at t _i = 10 μs, Q ≈ 109 kJ/mol at t _i = 100 μs and Q ≈ 66 kJ/mol at t _i = 1,000 μs). Textural relaxation data supported the higher damage efficiency for longer pulse duration.     

Storage Properties of Low Fat Fish and Rice Flour Coextrudates

In the present study, response surface method (RSM) and genetic algorithm (GA) were used to study the effects of process variables like screw speed, rpm (x ₁), L/D ratio (x ₂), barrel temperature (°C; x ₃), and feed mix moisture content (%; x ₄), on flow rate of biomass during single-screw extrusion cooking. A second-order regression equation was developed for flow rate in terms of the process variables. The significance of the process variables based on Pareto chart indicated that screw speed and feed mix moisture content had the most influence followed by L/D ratio and barrel temperature on the flow rate. RSM analysis indicated that a screw speed > 80 rpm, L/D ratio > 12, barrel temperature > 80 °C, and feed mix moisture content > 20% resulted in maximum flow rate. Increase in screw speed and L/D ratio increased the drag flow and also the path of traverse of the feed mix inside the extruder resulting in more shear. The presence of lipids of about 35% in the biomass feed mix might have induced a lubrication effect and has significantly influenced the flow rate. The second-order regression equations were further used as the objective function for optimization using genetic algorithm. A population of 100 and iterations of 100 have successfully led to convergence the optimum. The maximum and minimum flow rates obtained using GA were 13.19 × 10⁻⁷ m³/s (x ₁ = 139.08 rpm, x ₂ = 15.90, x ₃ = 99.56 °C, and x ₄ = 59.72%) and 0.53 × 10⁻⁷ m³/s (x ₁ = 59.65 rpm, x ₂ = 11.93, x ₃ = 68.98 °C, and x ₄ = 20.04%).     

Clostridium sporogenes-ATCC 7955 Spore Destruction Kinetics in Milk Under High Pressure and Elevated Temperature Treatment Conditions

Clostridium sporogenes (ATCC 7955) spores inoculated in milk (2% fat) were subjected to high-pressure (HP) treatments (700–900 MPa) and at elevated temperatures (80–100 °C) for selected times up to 32 min. Samples were sealed in 1-mL plastic vials and placed in a specially constructed insulated chamber to prevent temperature drop during the treatment. Both pressure pulse (with no hold time) and pressure hold techniques were employed for treatment. Pressure pulse resulted in a small, but consistent, destruction (up to 0.5 log kill) of spores. During the pressure hold treatment, the destruction followed a first-order model (R ² > 0.90). The kinetic data were compensated for the small variations in temperature during the treatment. As expected, higher pressures and higher temperatures resulted in a faster rate of spore destruction. Temperature-corrected D values ranged from 13.6 to 2.4 min at 700 MPa and 7.0 to 1.3 min at 900 MPa, respectively, with process temperatures set at 90 and 100 °C. In comparison, thermal treatments gave D values ranging from 156 min at 90 °C to 12.1 min at 100 °C. The temperature sensitivity Z _P values (16.5 to 20.3 °C) under high pressure (700–900 MPa) were higher than under conventional thermal processing (9.0 °C), indicating the spore’s thermal resistance to increase at HP processing conditions. The pressure sensitivity Z _T values varied between 450 and 680 MPa under the elevated temperature (80–100 °C) processing conditions. Overall, C. sporogenes 7955 spores were relatively more sensitive to temperature than pressure.     

Modeling and Optimization of Enzymatic Degradation of Aflatoxin B1 (AFB1) in Red Chili Powder Using Response Surface Methodology

Response surface methodology was used to optimize the peroxidase-catalyzed enzymatic degradation of aflatoxin B₁ (AFB₁) from red chili powder. Twenty experiments were carried out using central composite rotatable design with three independent variables (enzyme concentration, substrate or AFB₁ concentration, and incubation time) and single response (% aflatoxin B₁ degradation). The optimum conditions achieved after numerical and graphical optimizations for maximum percent degradation were: AFB₁ (31.5 nM), enzyme (13.5 U/nM AFB₁), and time (26 h). The actual percent degradation achieved at these optimum conditions was 70.0% and predicted 74.5%. The reduced quadratic model developed for the experimental data was found adequate to describe the relationships between the operating variables (Model F = 21.61, p < 0.001; F _lof = 3.63, p > 0.05). The robustness of the model was tested by confirmation experiments, and difference was found insignificant between the actual and predicted values as confirmed by two-tailed t test (α = 0.05). The hepatotoxic effect of the AFB₁ pre- and post-detoxification was tested on Wistar rats. The detoxified powder was also tested for changes in ascorbic acid, β-carotene, ASTA color value, and capsaicin content. Capsaicin was resistant to enzymatic degradation under specified conditions, but loss of around 15% was reported in color and β-carotene content; the loss in ascorbic acid was 10%.     

Thin Layer Drying of African Breadfruit (Treculia africana) Seeds: Modeling and Rehydration Capacity

African breadfruit (ABF) seeds are underutilized plant resources, which have been reported to have high potential for novel food and industrial uses. The kinetics of moisture removal during air drying of the whole (WS) and dehulled (DS) seeds was studied at temperatures of 40–70 °C. Five empirical models were tested for predicting the experimental data. Drying of ABF seeds followed an exponential decay pattern, while drying predominantly took place during the falling rate periods. All the drying models predicted the experimental data above 90% accuracy while the Henderson–Pabis model gave the best fit (0.95 < r ² < 0.99) at most of the experimental conditions. Effective moisture diffusivity, D _eff, ranged from 3.65 to 7.15 × 10⁻⁹ m²/s and 3.95 to 6.10 × 10⁻⁹ m²/s for WS and DS, respectively. D _eff showed significant dependence on the moisture content (p < 0.01). Rehydration capacity of DS was not significantly affected by drying temperature while that of WS increased with drying temperature.     

A sterilisation Time–Temperature Integrator based on amylase from the hyperthermophilic organism Pyrococcus furiosus

A candidate Time–Temperature Integrator (TTI) which is potentially suitable for use in validation of sterilisation processes was identified and tested. The TTI was based on the highly thermostable amylase produced from the extracellular medium of a Pyrococcus furiosus fermentation: this organism grows at temperatures in the region of 100 °C. Kinetic properties for the amylase following inactivation by heat showed it to be suitable for use as a sterilisation TTI. Isothermal kinetic data at 121 °C and non-isothermal kinetic data over the range 121 to 131 °C were determined. A decimal reduction time (D_T-value) at 121 °C of 24 min was calculated from isothermal tests and a range from 18.1 to 23.9 min from non-isothermal tests. A z-value of 10 °C was estimated from non-isothermal tests. Thus, sterilisation values (F₀) estimated from this TTI would be similar to F₀-values representative of the destruction of Clostridium botulinum spores. Industrial measurements under non-isothermal conditions were conducted in metal cans processed in an FMC reel and spiral cooker–cooler and a bar simulator, and also in plastic pouches processed in a Lagarde steam-air retort.Industrial relevanceMany food processes, such as canning, are based upon thermal sterilisation of the food material. The development of a reliable Time–Temperature Integrator for such a process would be industrially valuable by providing a simple way of validating such processes. This study demonstrates the feasibility of one such TTI.     

Study of the diffusion coefficients of diphenylbutadiene and triclosan into and within meat

The migration of two chemicals, diphenylbutadiene and triclosan, was the target of this paper. Pork meat with different fat contents was prepared to study the influence of this parameter in the migration levels and to study the rate of diffusion of these migrants into the whole plastic/foodstuffs system and within the foodstuff. The whole system plastic/foodstuff diffusion coefficient (effective D) was calculated according to an equation based on the Fick’s Second Law, and D within the foodstuff (D _F) was calculated according to the Moisan equation. At 5 °C, D _F was 1.6 × 10⁻⁷ and 1.7 × 10⁻⁷ cm²/s for DPBD and triclosan, respectively. At 25 °C, D _F was 3.7 × 10⁻⁷ and 3.9 × 10⁻⁷ cm²/s for DPBD and triclosan, respectively. As expected, D within the pork meat is faster than the whole system D, which means that the interface plastic/foodstuff may be the limiting step for the mass transport of chemicals from the packaging to the foodstuff.     

Structural Relaxation of Salmon Gelatin Films in the Glassy State

Mechanical relaxation of glassy carbohydrates has been reported extensively in the literature; however, little work is available on protein-based systems. This study deals with the structural relaxation of salmon (Salmo salar) gelatin in the glassy state. Skin gelatin was obtained by an acid–alkaline extraction method. Molecular weight (M _w) was determined by capillary viscometry. Films prepared by casting (7% w/v) were equilibrated to a moisture content of ~18.4% (db). The glass transition temperature (T _g) and enthalpic relaxation were determined by differential scanning calorimetry (DSC). Mechanical properties were assessed using a texture analyzer at constant temperature and moisture content. DSC showed a T _g ~34°C, and the selected storage temperature (T _a ) was 29°C (T _g − T _a = 5°C). The films were aged for 0, 4, 8, 16, and 40 h. Viscometry produced values of M _w ~90.2 kDa. The stress relaxation was modeled by the Kohlrausch–Wlliams–Watts (KWW) equation, reporting an increase in relaxation time (τ ₀) as the ageing time increased (τ ₀ ~6.41E + 03 s for 0 h; τ ₀ ~9.01E + 05 s for 40 h). β parameter was smaller for the aged films, indicating a spread of relaxation times. The derivative of KWW equation (dφ/dt) indicated a more rapid relaxation in a fresh sample compared with aged films. DSC showed an excess in enthalpy (ΔH) on the aged samples due to the non-equilibrium state of the matrix. ΔH increased with ageing time with values of ΔH ~2.42 J/g for the films aged for 40 h. This work demonstrated molecular relaxation process of gelatin in the glassy state, which must be taken into account if this material is used as a structure forming matrix.     

Thermal Transition Properties of Spaghetti Measured by Differential Scanning Calorimetry (DSC) and Thermal Mechanical Compression Test (TMCT)

Glass transition temperature (T _g) of spaghetti sample was measured by thermal and rheological methods as a function of water content from 0 to 70 kg/100 kg spaghetti. In the cases of sample containing un-freezable water (i.e., amount of water which did not form ice even at very low temperature), calorimetric measurements performed by differential scanning calorimetry showed that the T _g values decreased from 142.8 to 42.7 °C when water content increased from 0 to 13.95 kg/100 kg spaghetti, respectively. Glass transition temperature increased with the increase of heating rate (2–50 °C/min) and reached to a nearly constant value above 30 °C/min. Thermal mechanical compression test showed relatively lower T _g values compared to the DSC values at low moisture contents, whereas at high moisture content T _g showed higher values. In the cases of samples containing freezable water (27–70 kg/100 kg spaghetti), glass transition shifts were merged with the ice melting endotherm. The freezing point, measured from the endothermic peak, decreased with the decrease of water content. In the state diagram, maximal freeze-concentration condition was determined as X_\texts￠ X_{\text{s}}^\prime =0.81 kg/kg spaghetti from the intersection of the extended freezing curve and a horizontal line passing thru T_\textm￠ T_{\text{m}}^\prime  = −10.3 °C.     

The effect of Cd and vitamin D3 on the solidity of eggshell

 The effect of cadmium and vitamin D₃ on the solidity of eggshells was observed. Laying hens were divided into 7 groups with 10 animals per group. In the experimental groups 1, 2, and 3, we administered daily 0.3; 10.0, and 15.0 mg CdCl₂ kg^–1 body weight, respectively; in experimental groups 4, 5, and 6 were administered the same CdCl₂ concentrations as above supplemented with a preventive dose of vitamin D₃ Group 7 was the control group. In groups 1, 2, and 3, the mean values of solidity were 29.50; 27.58, and 27.34 N/cm². In the control group, the mean value was 34.05 N/cm². In the experimental groups 4, 5, and 6, supplemented with vitamin D₃ and cadmium, the values were significantly higher: 34.26, 30.59, and 29.48 N/cm², respectively It is obvious that the interaction of vitamin D₃ with Cd reduced an adverse effect of cadmium. Received: 14 February 2000 / Revised version: 15 May 2000     

Modification of Food-Contacting Surfaces by Plasma Polymerization Technique: Reducing the Biofouling of Microorganisms on Stainless Steel Surface

In this study, the prevention of the attachment of test microorganism Enterobacter sakazakii onto stainless steel (SS 316) surfaces by radio frequency (RF) plasma polymerization (PlzP) technique using several hydrophilic monomers as precursors was reported. Different plasma conditions (RF discharge power of 20–80 W with exposure time of 10 min) were employed during the modifications. PlzP-modified surfaces were characterized in detail by static contact angle measurements in order to state the change of surface hydrophilicity. The surface topology of unmodified and PlzP [ethylenediamine (EDA)]-modified SS 316 plates was characterized by atomic force microscopy. The attachment of the model microorganism on the SS 316 surface modified by plasma using EDA at 45 W and 10 min was reduced by 99.74% in comparison to the unmodified control surface. For equilibrium adsorption behavior, Freundlich and Langmuir models were attempted and model parameters for Freundlich (K _F and 1/n) and for Langmuir (a and b) were obtained. The values of the K _F and 1/n were 5.6 and 0.58 and 0.9 and 0.39, respectively; the values of a and b were 25 × 10⁴ and 1.82 × 10⁻⁸ and 0.3 × 10⁴ and 7.96 × 10^-8, for bare and PlzP-EDA-modified SS 316 surfaces, respectively. As a result, PlzP technique was found to be an alternative simple method to decrease the microbial attachment and create bacterial anti-fouling surfaces.     

Thermal Resistance of Bacillus coagulans in Double Concentrated Tomato Paste

Thermal resistance was determined on a strain of Bacillus coagulans in double concentrated tomato paste (a_w= 0.95 at 23°C, pH = 4.0, 30.3°Brix, 70.1% moisture and acidity 1.30 g/100g citric acid. A microsyringe method was used with an inoculum of 1.3 × 10⁴ spores/ mL. Values of D_90°c= 3.5 min and z = 9.5C° were obtained.     

Optimization of supercritical CO2 extraction of phytosterol-enriched oil from Kalahari melon seeds

Supercritical carbon dioxide (SC-CO₂) extraction of oil from Kalahari melon seeds was investigated in this study. Response surface methodology was applied to model and optimize the extraction, namely pressure (200–400 bar), temperature (40–80 °C), and supercritical fluid flow rate (10–20 mL/min). Well-fitting models were successfully established for oil recovery (R ² = 0.9672) and phytosterol concentration (milligrams per 100 g; R ² = 0.8150) through multiple linear regressions with backward elimination. The effect of supercritical fluid flow rate was the most significant (P < 0.05) factor that affected oil recovery but this factor had no significant (P > 0.05) effect on phytosterol concentration. The optimal processing conditions for oil recovery and phytosterol concentration were pressure of 300 bar, temperature at 40 °C, and supercritical fluid flow rate of 12 mL/min. These optimal conditions yielded a 76.3% oil recovery and 836.5 mg/100 g of phytosterol concentration. The oil content in the Kalahari melon seeds as estimated by Soxhlet extraction was around 30.5/100 g. The phytosterol concentration in the oil extracted with SC-CO₂ extraction was 94% higher than that obtained with solvent extraction.     

Measurement of optical absorbance of Clostridium sporogenes PA 3679 spores as a method for determining their thermal inactivation

 The loss of optical density of Clostridium sporogenes PA 3679 spores after heating at temperatures of 121, 126, 130 and 135°C was studied, together with the relationship between this parameter and the recovery capacity of the heated spores. The results show that the spores suffered a greater loss of optical density when they were subjected to more severe heating. A linear relationship was observed between the loss of viability and the optical absorbance of the spores. A certain parallel was detected between the heat resistance parameters of the spores D_T (decimal reduction time) and z (thermal inactivation coefficient), and the kinetic parameters D_T ^A and z^A, which describe the reduction in absorbance. Received: 14 April 1997     

Measurement of optical absorbance of Clostridium sporogenes PA 3679 spores as a method for determining their thermal inactivation

 The loss of optical density of Clostridium sporogenes PA 3679 spores after heating at temperatures of 121, 126, 130 and 135°C was studied, together with the relationship between this parameter and the recovery capacity of the heated spores. The results show that the spores suffered a greater loss of optical density when they were subjected to more severe heating. A linear relationship was observed between the loss of viability and the optical absorbance of the spores. A certain parallel was detected between the heat resistance parameters of the spores D_T (decimal reduction time) and z (thermal inactivation coefficient), and the kinetic parameters D_T ^A and z^A, which describe the reduction in absorbance. Received: 14 April 1997     

Response surface methodological study of esterification of lactic acid with palmitic acid catalyzed by immobilized lipases from Mucor miehei and porcine pancreas

X _s), enzyme/substrate (E/S) ratios (X _e) and incubation time (X _t) on the preparation of palmitoyl lactic acid using Mucor miehei lipase (MML) and porcine pancreas lipase (PPL). Experimental ester yields were found to be in good agreement with predictions. In the case of MML, the ester yield was found to increase with X _e and X _t and a maximum yield of 27 mM was obtained at X _e=128 activity units(AU)/mM of substrate, X _s=64–74 mM and X _t=72 h. In the case of PPL, the ester yield was found to increase with increases in X _e and X _s. Optimum conditions for PPL were X _e=45 AU/mM, X _s=85–90 mM and X _t=72 h, at which the maximum ester yield of 15 mM was obtained. Received: 14 April 1999 / Revised version: 2 September 1999     

Determination of Histamine in Some Foods by Isotachophoretic Method with Simple Sample Preparation

A one-dimensional capillary isotachophoretic method in cationic system of the separation has been applied for histamine determination in food samples. The proposed electrolyte system consisted of 0.01 M potassium hydroxide with l-valine to pH = 9.9 as the leading electrolyte and 0.02 M 2-amino-2-hydroxymethyl-propane-1,3-diol adjusted to pH = 8.3 with 0.1 M hydrochloric acid as terminating electrolyte. Proposed method was characterized by linearity range 5–50 mg L⁻¹ and R ² = 0.9982, accuracy (recoveries ranged from 95% to 102%), detection (2.10 mg L⁻¹), and quantification (7.01 mg L⁻¹) limits. The sample preparation for proposed electrophoretic method included only simple extraction with trichloroacetic acid with filtration and derivatisation stage are avoided. The histamine concentration was determined in meat (turkey, chicken, beef and pork) and meat products (ripened sausage and dry-cured ham), fish (smoked salmon and mackerel), and different kind of mildew and mold ripened cheeses samples. The histamine content ranged from not detected level for fresh meat to 29.63 mg 100 g⁻¹ for cheese samples. The reversed phase HPLC was applied as reference method and the F-Snedecor test and the t test were employed to compare the precision and accuracy of the both methods. Positive correlations were found between the two analytical methods for histamine determination in food products. The obtained results indicate that the proposed electrophoretic method is simple, precise, accurate, and convenient.     

Nano Zinc Oxide-Loaded Calcium Alginate Films with Potential Antibacterial Properties

In this work, zinc oxide nanoparticles-loaded calcium alginate films were investigated for their moisture uptake behavior at different temperatures. The equilibrium uptake data was interpreted quantitatively by GAB isotherm models. The monolayer moisture contents were 0.301 ± 0.003, 0.0214 ± 0.092, and 0.171 ± 0.102 at 20, 30, and 37°C, respectively. The water vapor transmission rate was found to be 0.816 ± 0.143, 1.42 ± 0.045, and 1.632 ± 0.064 g s⁻¹ m⁻² respectively. For the moisture content range of 0.2 to 0.6, the net ∆H and ∆S values were found to be 22.73 to 11.14 KJ/mol and 0.064 to 0.034 KJ/mol/K, respectively. The moisture uptake of films increased with water activity but showed negative temperature dependence. The enthalpy of sorption (∆H) and differential entropy (∆S) were determined at different moisture content values, ranging from 0.2 to 0.6 g/g db. The two parameters showed a higher degree of correlation. The equilibrium moisture content data was used to evaluate harmonic mean temperature T _hm. Finally, the biocidal action of films was tested against model bacteria Escherichia coli.     

Inactivation of polyphenol oxidase from Pacific white shrimp by dense phase carbon dioxide

The inactivation of polyphenol oxidase (PPO) from Pacific white shrimp exposed to dense phase carbon dioxide (DPCD) treatment was investigated. PPO activity showed a dramatic loss at 4–25 MPa and 37 °C. At the lower pressure (4–15 MPa), the experimental data of inactivation followed the first-order reaction kinetic model, the pressure sensitivity (Z_P) of the kinetic parameters was 49.02 MPa and the activation volume (△ V^≠) was − 120.88 cm³/mol. At the higher pressure (20 and 25 MPa), the experimental data of inactivation followed the biexponential kinetic model. The kinetic rate constant k_F and k_S of fast and stable fractions were 2.45 and 0.08 min^{− 1}, respectively. The decimal reduction time D_F and D_S were 0.94 and 29.43 min at 25 MPa and 37 °C, respectively. After DPCD treatment, the loss activity of PPO had no restoration storing for 6 days at 4 °C. The results of SDS-PAGE and activity staining also showed that DPCD treatment had the obvious inhibitory effect on PPO from Pacific white shrimp. The PPO activity in vivo was easier to be inactivated than that in crude PPO extracts under the same DPCD treatment conditions.

Industrial relevance

There is a growing interest in non-thermal pasteurization methods, which could retain food's freshlike physical, nutritional, and sensory qualities. Pacific white shrimp accounts for 90% of the global aquaculture shrimp production, they are becoming increasingly popular. However, enzymatic browning of shrimp has been of great concern to food scientists and food processors. Dense phase carbon dioxide (DPCD) may be an adequate tool to obtain high quality since PPO activity could not be inactivated totally by high pressure under 400 MPa yet. The present work deals with the inactivation of PPO from Pacific white shrimp exposed to DPCD treatment in order to explore the feasibility of shrimp by DPCD process.