Development of an in-house method for the incorporation of model migrants in polyethylene films and determination of diffusion constants in food

Two methods were tested and compared for the additivation of low density polyethylene (LDPE). The aim was to obtain highly contaminated plastic films to enable the study of migration (diffusion and partition phenomena). One of the methods involved immersion of low density polyethylene (LDPE) films in a concentrated solution of the selected substances. The other method involved achieving close contact of plastic films with a polyethylene wax contaminated with the selected compounds. The PE-wax method provided better results as regards the final concentration and homogeneity of the contaminants in the plastic films (deviations between replicates for each plastic film was lower than 10% for both migrants tested). This method was therefore considered suitable for preparing a homogeneous additive release system. Finally, to test the applicability of the method, concentration profiles were studied in chocolate spread placed in contact with the contaminated films, and diffusion coefficients were estimated in this foodstuff. Estimated diffusion coefficients were 4.6 × 10⁻⁰⁷ cm²/s for DPBD and 3.2 × 10⁻⁰⁷ cm²/s for triclosan in the same conditions.     

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.     

Electrochemical sensor based on Prussian blue nanorods and gold nanochains for the determination of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

In this paper, a novel electrochemical sensor for the detection of H₂O₂ was proposed based on gold nanochains and prussian blue nanorods (PB@MWCNTs), which were synthesized with multiwall carbon nanotubes (MWCNTs) as a template. With the introduction of MWCNTs and the gold nanochains, the proposed system shows synergy among the Prussian blue (PB), MWCNTs, and the gold nanochains, which amplifies the H₂O₂ sensitivity greatly. A linear range from 1.75 × 10⁻⁶ to 1.14 × 10⁻³ M with a detection limit of 0.5 × 10⁻⁶ M (S/N = 3) and a high sensitivity 300 μA mM⁻¹ cm⁻² for H₂O₂ detection is obtained. Moreover, the sensor exhibits good repeatability and stability.     

Application of Catalytic Hydrogen Evolution in the Presence of Neonicotinoid Insecticide Clothianidin

Clothianidin, a new generation of pesticide, was determined in spiked tap water, apple juice, and soil by square-wave adsorptive stripping voltammetry. The method of determination is based on the hydrogen evolution reaction catalyzed by clothianidin at the hanging mercury drop electrode. The optimal signal was detected at −1.4 V versus Ag/AgCl in citrate buffer at pH 2.2. Various parameters such as pH, buffer concentration, frequency, amplitude, step potential, accumulation time, and potential were investigated to enhance the sensitivity of the determination. The optimal results were recorded at an accumulation potential of −0.35 V, accumulation time of 7 s, amplitude of 100 mV, frequency of 200 Hz, and step potential of 7 mV. The mechanism of catalytic hydrogen evolution was considered under experimental and theoretical conditions. This electroanalytical procedure enabled to determine clothianidin in the concentration range 9 × 10⁻⁹–4 × 10⁻⁶ mol L⁻¹ in supporting electrolyte and tap water, 1 × 10⁻⁷–4 × 10⁻⁶ mol L⁻¹ in diluted apple juice, and 2 × 10⁻⁷–1 × 10⁻⁶ mol L⁻¹ in soil. The detection and quantification limits in supporting electrolyte and diluted apple juice were found to be 2.6 × 10⁻⁹, 8.6 × 10⁻⁹ and 3 × 10⁻⁸, and 1 × 10⁻⁷ mol L⁻¹, respectively. A standard addition method was successfully used to determine clothianidin in spiked tap water, spiked apple juice, and spiked soil.     

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%).     

Effects of Characteristics Changes of Collagen on Meat Physicochemical Properties of Beef Semitendinosus Muscle during Ultrasonic Processing

Low-frequency and high-power ultrasound (40 kHz, 1,500 W) was tested for its effects on the characteristics of intramuscular heat-insoluble collagen and meat quality and textural properties of beef semitendinosus muscle. Meat steaks (2.5 × 5.0 × 5.0 cm, 100 ± 5 g) were sonicated for 10, 20, 30, 40, 50, and 60 min, respectively. Characteristics changes of collagen and meat quality and texture were estimated. The results indicated that ultrasound treatment had no significant (P > 0.05) effects on L* (lightness) and a* (redness) values but decreased b* (yellowness) value significantly when sonicated for 30 min (minimum 6.98). Ultrasound treatment significantly (P < 0.01) reduced the muscle fiber diameter and filtering residues but had no significant effects on the content of heat-insoluble collagen. Significant differences (P < 0.05) in β-galactosidase and β-glucuronidase activity were found between ultrasound treated for 10 min (reached the minimum were 5.2 × 10⁻³ and 1.6 × 10⁻³ umol∙ml⁻¹∙min⁻¹, respectively) and control samples. Thermal characteristics analysis of collagen suggested that ultrasound treatment weaken the average stability of collagen. After ultrasound treatment, collagenous fibers were disordered and staggered significantly; fiber arrangement became loose; and the denaturing, granulation, and aggregation of collagen fiber appeared in the extracellular space. Those changes on collagen characteristics had significant effects on meat textural properties. The results suggested that low-frequency and high-power sonication had a significant effect on collagen characters and meat textural properties.     

Enzymatic Catalytic Spectrophotometric Determination of Thiamine in Food

A highly sensitive and simple spectrophotometric method for the determination of thiamine based on inhibitory effect of thiamine on the hemoglobin-catalyzed reaction of H₂O₂ with acid chrome blue K was developed. The concentration of thiamine is linear with the percentage inhibition of system under the optimal experimental conditions. The calibration curve is linear in the range 3 × 10⁻⁷ to 3.00 × 10⁻⁵ M with the detection limit of 1.2 × 10⁻⁸ M. This method can be used for the determination of thiamine in food with satisfactory results.     

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.     

Supercritical CO<Subscript>2</Subscript> extraction of <Emphasis Type="Italic">Alkanna</Emphasis> species and investigating functional characteristics of alkannin-enriched yoghurt during storage

Alkannin is a potent pharmaceutical substance with a wide spectrum of biological activities. In the scope of this study, supercritical CO₂ extraction and sonication with hexane were applied to various Alkanna species, which were then subjected to hydrolysis. Total alkannins were quantified by HPLC/DAD and incorporated into yoghurt. Viscosities, pH values and microbial analyses were reported at 7 days of intervals for 21 days of storage. A. tinctoria possessed the highest amounts of alkannins and total phenols (686.3 mg GAE/g extract). The results revealed no significant changes in pH values (4.1–4.0), viable counts of Streptococcus salivarius ssp. thermophilus (80–150 × 10⁶ cfu g⁻¹) and slightly lower viscosities of enriched yoghurts (8,250–6,750 cPs) compared with the control (4.15–4.0; 110–105 × 10⁶ cfu g⁻¹; 12,600–11,310 cPs) during storage. However, viable counts of Lactobacillus delbrueckii ssp. bulgaricus of enriched yoghurts (87 × 10³ cfu g⁻¹) were much better than the control (191 × 10³ cfu g⁻¹), indicating a significant decrease in post acidification and generation of bitter peptides. Among the species investigated, A. tinctoria is the most promising source, obtained at higher yields via supercritical fluid extraction technology as a green alternative to solvent extraction and thus can be utilized at industrial scale in order to develop yoghurt products with improved health benefits.     

Stability and Degradation Kinetics of Bioactive Compounds and Colour in Strawberry Jam during Storage

The effect of storage time and temperature on degradation of bioactive compounds such as ascorbic acid, anthocyanins, total phenols, colour and total antioxidant capacity of strawberry jam were investigated. The results indicated that lightness (L) value decreased significantly (p < 0.05) over 28 days of storage at 4 and 15 °C, with lower values measured at higher temperatures. Anthocyanins, ascorbic acid and colour degradation followed first-order kinetics where the rate constant increased with an increase in the temperature. The reaction rate constant (k) increased from 0.95 × 10⁻² day⁻¹ to 1.71 × 10⁻² day⁻¹ at 4 and 15 °C for anthocyanins. Similarly, k increased from 2.08 × 10⁻² day⁻¹ to 4.54 × 10⁻² day⁻¹ at 4 and 15 °C for ascorbic acid. In general, total antioxidant activity for strawberry jam samples stored for 28 days at 4 and 15 °C exhibited lower values as compared to control (day 0). The results showed greater stability of nutritional parameters at 4 °C compared to 15 °C.     

Determination of Rosmarinic Acid by High-Performance Liquid Chromatography and Its Application to Certain Salvia Species and Rosemary

This study describes a method development for the determination of rosmarinic acid (RA) by using a gradient high-performance liquid chromatography (HPLC) and its application to certain plant materials. The analysis was performed by utilizing a two solvents system [A: methanol/water/formic acid (10:88:2; v:v:v); B: methanol/water/formic acid (90:8:2; v:v:v)] on a reverse-phase column. The flow rate and injection volume were 1 ml min⁻¹ and 10 μl, respectively. Signals were detected at 280 nm. In addition, an internal standard (IS) technique was applied for the analysis of RA to increase precision, and propylparaben was employed for this purpose. The repeatability results as RSD% were 1.66, 1.17 and 1.26 for intra-day and 1.38 was for inter-day with the employment of (3.67 × 10⁻⁵ M) RA. A limit of linearity (LOL) was observed in a wide (1.13 × 10⁻⁵–5.65 × 10⁻⁴ M) concentration range. Linearity parameters were also examined in the range of 5.95 × 10⁻⁶–7.14 × 10⁻⁵ M RA, and very good correlation was observed. The limit of detection (LOD) and limit of quantification (LOQ) (for inter-day) were 1.60 × 10⁻⁶ M (signal/noise [S/N] = 3.3) and 4.80 × 10⁻⁶ M (S/N = 10), respectively. The method was applied to the extracts of certain Lamiaceae plants (Salvia candidissima Vahl. subsp. candidissima, S. sclarea L., S. verticillata L. subsp. verticillata and R. officinalis L.), and reasonable results were obtained.     

Quenching of excited states of red-pigment zinc protoporphyrin IX by hemin and natural reductors in dry-cured hams

Zinc protoporphyrin IX (ZnPP), the major red pigment in hams dry-cured without nitrates/nitrites, is an efficient photosensitizer, which upon absorption of visible light forms short-lived excited singlet state (¹ZnPP*) and by intersystem crossing yields the very reactive triplet-excited state (³ZnPP*). Using nano-second laser flash photolysis and transient absorption spectroscopy NADH, ascorbic acid, hemin and dehydroascorbic acid were each found to be efficient quenchers of ³ZnPP*. The deactivation followed, in homogeneous dimethyl sulfoxide (DMSO) or DMSO:water (1:1) solutions, second-order kinetics. The rate constant for ascorbic acid and NADH for reductive quenching of ³ZnPP* was at 25 °C found to be 7.5 ± 0.1 × 10⁴ L mol⁻¹ s⁻¹ and 6.3 ± 0.1 × 10⁵ L mol⁻¹ s⁻¹, respectively. The polyphenols catechin and quercetin had no effect on ³ZnPP*. The quenching rate constant for oxidative deactivation of ³ZnPP* by dehydroascorbic acid and hemin was at 25 °C: 1.6 ± 0.1 × 10⁵ L mol⁻¹ s⁻¹ and 1.47 ± 0.1 × 10⁹ L mol⁻¹ s⁻¹, respectively. Oxidized glutathione did not act as an oxidative quencher for ³ZnPP*. After photoexcitation of ZnPP to ¹ZnPP*, fluorescence was only found to be quenched by the presence of hemin in a diffusion-controlled reaction. The efficient deactivation of ³ZnPP* and ¹ZnPP* by the metalloporphyrin (hemin) naturally present in meat may accordingly inherently protect meat proteins and lipids against ZnPP photosensitized oxidation.     

Kinetics of Mass Transfer in Microwave Precooked and Deep-Fat Fried Ostrich Meat Plates

The aim of this study was to evaluate the effect of microwave precooking on mass transfer during deep-fat frying of ostrich meat plates. The influence of microwave power level, frying temperature, and time on mass transfer was determined. Among all treatments, the plates being precooked at 5.23 W/g of microwave power and then deep-fat fried at 135 °C had the minimum fat content. The effective moisture diffusivity ranged between 1.47 × 10⁻⁸ and 4.17 × 10⁻⁸ m²/s. Fat transfer rate constant was in the range of 0.024 and 19.708 s⁻¹. The activation energy obtained from Arrhenius plot for the effective moisture diffusivity ranged between 38.84 and 51.07 kJ/mol.     

Sugarcane spirit extracts of oak and Brazilian woods: antioxidant capacity and activity

Sugarcane spirit extracts of six different Brazilian woods for potential use in manufacturing aging casks were compared with similar extracts of five oak samples from different geographic origin and heat treatment regarding: (1) content of phenolics and copper; (2) radical reducing capacity and reactivity toward 2,2-diphenyl-1-picrylhydrazyl radical (DPPH·); and (3) effect on the rate of oxygen depletion rate in a peroxidating lipid model system. Total phenolic contents of the Brazilian wood extracts ranged from 0.65 (canela-sassafrás) to 6.4 (jatobá) mmol_GAE L⁻¹ and from 1.39 to 2.87 mmol_GAE L⁻¹ for oak extracts. Flavonoids ranged from 1.54 × 10⁻⁴ (ipê) to 6.5 × 10⁻² (oak) mmol_rutin L⁻¹, and tannins from below the detection limit to 0.22 (jatobá) mmol_{tannic acid} L⁻¹. Correlation was observed for the antioxidant capacity versus phenolics/flavonoids/tannins content, where oak extracts exhibit the highest radical scavenging capacity compared to Brazilian woods. Rate constant for radical scavenging by the extracts ranged from 4.9 × 10³ M⁻¹ s⁻¹ (canela-sassafrás) to 9.7 × 10⁴ M⁻¹ s⁻¹ (oak). The oxygen consumption index showed the Brazilian woods amendoim and jatobá to be more efficient inhibitors than the oak extracts for lipid autoxidation initiated by metmyoglobin, despite that the oak extracts seem to be more efficient to scavenge DPPH·. No simple correlation with phenolics or copper content could be established, and a prooxidative tendency was observed for the extracts of canela-sassafrás, castanheira, and louro-canela.     

Polysaccharide/Protein Nanomultilayer Coatings: Construction,Characterization and Evaluation of Their Effect on ‘Rocha’ Pear (<Emphasis Type="Italic">Pyrus communis</Emphasis> L.) Shelf-Life

Nanolayered coatings of κ-carrageenan, a polysaccharide with good gas barrier properties, and lysozyme, a protein with antimicrobial action, were in a first stage assembled on aminolysed/charged polyethylene terephthalate (PET) pieces, which acted as a support, by alternate five-layer deposition. This was performed to allow the characterization of the nanomultilayer system. PET aminolysis was confirmed by Fourier transform infrared spectroscopy and contact angle, and the subsequent layer adsorption on aminolysed PET surface was confirmed by absorbance, contact angle and SEM images. The water vapour permeability and the oxygen permeability (O₂P) of the five layers were found to be 0.013 ± 0.003 × 10⁻¹¹ and 0.1 ± 0.01 × 10⁻¹⁴ g m⁻¹ s⁻¹ Pa⁻¹, respectively. The nanomultilayer system was subsequently applied (without PET support) directly on ‘Rocha’ (Pyrus communis L.) fresh-cut pears and whole pears. Uncoated fresh-cut pears and whole pears presented higher mass loss, higher total soluble solids (TSS) and lower titratable acidity when compared with coated fresh-cut pears and whole pears. Uncoated fresh-cut pears also presented a darker colour. These results showed that the nanolayered coating assembled on the fruits’ surface has a positive effect on fruit quality and contributed to extend the shelf-life.     

Influence of ultrasound on mass transport during cheese brining

 The effect of ultrasound on mass transfer during cheese brining has been investigated. The rate of water removal and NaCl gain increased when ultrasound was applied in comparison with brining performed under static or dynamic conditions, suggesting that ultrasound improves both external and internal mass transfer. A simple diffusional model was developed to simulate mass transport during acoustic brining. Model parameters were estimated using experimental data from acoustic brining experiments carried out on cheese cylinders of 1.7×10^–2m radius and 3×10^–2 m height at different temperatures (5, 15 and 20  °C). Effective water (D _W) and NaCl (D _S) diffusivities estimated using the proposed model ranged from 5.0×10^–10m²/s and 8.0×10^–10 m²/s at 5  °C to 1.3×10^–9m²/s and 1.2×10^–9 m²/s at 20  °C. Both D _W and D _S varied with temperature according to the Arrhenius equation. Through the proposed model, water losses and NaCl gains of the experiments used in the parameter identification were accurately simulated (average %var=98.2%) and also of two additional acoustic experiments carried out under different conditions of temperature (10  °C) and sample size and geometry [parallelepiped of (6×2.5×1.25)×10^–2 m] to those used in the parameter identification (average %var=98.4%). Received: 22 September 1998 / Revised version: 20 November 1998     

Optimization and Modeling of Process Parameters for Lipase Production by Bacillus brevis

Statistical evaluation of fermentation conditions and nutritional factors by Plackett–Burman two-level factorial design followed by optimization of significant parameters using response surface methodology for lipase production by Bacillus brevis was performed in submerged batch fermentation. Temperature, glucose, and olive oil were found to be the significant factors affecting lipase production. Maximum lipase activity of 5.1 U ml⁻¹ and cell mass of 1.82 g l⁻¹ at 32 h were obtained at the optimized conditions of temperature, 33.7 °C; initial pH, 8; and speed of agitation, 100 rpm, with the medium components: olive oil, 13.73 ml l⁻¹; glucose, 13.98 g l⁻¹; peptone, 2 g l⁻¹; Tween 80, 5 ml l⁻¹; NaCl, 5 g l⁻¹; CH₃COONa, 5 g l⁻¹; KCl, 2 g l⁻¹; CaCl₂·2H₂O, 1 g l⁻¹; MnSO₄·H₂O, 0.5 g l⁻¹; FeSO₄·7H₂O, 0.1 g l⁻¹; and MgSO₄·7H₂O, 0.01 g l⁻¹. The lipase productivity and specific lipase activity were found to be 0.106 U (ml h)⁻¹ and 2.55 U mg⁻¹, respectively. Unstructured kinetic models and artificial neural network models were used to describe the lipase fermentation. The kinetic analysis of the lipase fermentation by B. brevis shows that lipase is a growth-associated product.     

Evaluation of Protease-producing Ability of Fish Gut Isolate Bacillus cereus for Aqua Feed

Extracellular protease production by Bacillus cereus isolated from the intestine of fish Mugil cephalus has been investigated in shake-flask experiment using different preparations of tuna-processing waste such as raw fish meat, defatted fish meat, alkali hydrolysate, and acid hydrolysate as nitrogen source. Among the tuna preparations tested, defatted fish meat supported the maximum protease production (134.57 ± 0.47 U ml⁻¹), and 3% concentration of the same was found to be optimum for maximizing the protease production (178.50 ± 0.28 U ml⁻¹). Effect of carbon sources on protease production in the optimized concentration of defatted tuna fish meat revealed that galactose aided the higher protease production (259.83 ± 0.04 U ml^–1) than the other tested carbon sources and a concentration of 1.5% galactose registered as optimum to enhance the protease production (289.40 ± 0.16 U ml⁻¹). The halotolerancy of B. cereus for protease production indicated that 3% of sodium chloride was optimum to yield maximum protease (301.63 ± 0.20 U ml⁻¹). Among the surfactants tested, protease production was high in Triton X 100-added medium (298.63 ± 0.12 U ml⁻¹) when compared to other surfactants, and its optimum concentration recorded was 0.8% (320.57 ± 0.17 U ml⁻¹) for more protease production. Partial characterization of crude enzyme revealed that pH 7.0 (278.90 ± 0.08 U ml⁻¹) and 60°C temperature (332.37 ± 0.18 U ml⁻¹) were optimum for better protease activity by B. cereus.     

Characterization of Main Anthocyanins Extracted from Pericarp Blue Corn by MALDI-ToF MS

The anthocyanic composition of pigmented Mexican corn (Zea mays) has been investigated. Two extracts (hydrolyzed and non-hydrolyzed) were analyzed by HPLC at different temperatures. The separation profile obtained in chromatography was different for minor components but the main fraction was the same in both cases. The last anthocyanin fraction was collected and analyzed by MALDI-ToF MS. The compounds identified in the fraction were cyanidin-3-glucoside and pelargonidin-3-glucoside with an approximate content of 1 × 10⁻⁶ and 1 × 10⁻⁷ M for the hydrolyzed and non-hydrolyzed, respectively.