Hydrolysis of sucrose by invertase immobilized on nylon-6 microbeads

A commercial extracellular invertase (EC 3.2.1.26) from Saccharomyces cerevisiae has been inmobilized by covalent bonding on novel microbeads of nylon-6 using glutaraldehyde. The enzyme was strongly bound on the support, immobilized with an efficiency factor of 0.93. The biocatalyst showed a maximum enzyme activity when immobilized at pH 5.0, but optimum pH activity for both immobilized and free invertases was 5.5. The optimum temperatures for immobilized and free enzymes were 60 and 65 °C, respectively. Kinetic parameters were determined for immobilized and free invertases: V_max values were 1.37 and 1.06 mmol min⁻¹ mg⁻¹, respectively. The K_m and K_i values were 0.029 and 0.71 M for immobilized invertase and 0.024 and 0.69 M for free invertase. It was found that the thermal stability of the immobilized invertase with regard to the free one increased by 25% at 50 °C, 38% at 60 °C and 750% at 70 °C. The immobilized biocatalyst was tested in a tubular fixed-bed reactor to investigate its possible application for continuous sucrose hydrolysis. The effects of two different sugar concentrations and three flow rates on the productivity of the reactor and on the specific productivity of the biocatalyst were studied. The system demonstrated a very good productivity up to 2.0 M sugar concentration, with conversion factors of 0.95 and 0.97, depending on sucrose concentration in the feeding. This approach may serve as a simple technique and can be a feasible alternative to continuous sucrose hydrolysis in a fixed bed reactor for the preparation of fructose-rich syrup.     

Analysis of volatile nitrosamines from a model system using SPME–DED at different temperatures and times of extraction

Solid-phase microextraction (SPME) coupled to a direct extraction device (DED) was evaluated as a method for extracting nitrosamine (NA) standard mix containing nine volatile nitrosamines from a solid food model system using several temperatures and times of extraction. The efficacy of extraction, the linearity of response and the sensitivity of this method for analysis of NA were determined at refrigeration (4 °C) and room (25 °C) temperature. Several extraction times (15, 30, 60,120 and 180 min) were also tested. Analysis was carried out with gas chromatography–mass spectrometry (GC–MS) in selected ion monitoring (SIM) mode. At 4 °C all NA were detected at all concentrations studied (ranged from 1 to 50 ng ml⁻¹) except for N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR) and N-nitrosodiphenilamine (NDPheA). Better results were obtained at 25 °C in terms of efficacy of extraction, linearity values (regression coefficients, R²) and sensitivity values (limit of detection, LOD). Only 15 min of extraction time were enough to extract all NA from gelatines (10 ng ml⁻¹) at 25 °C. None of the NA reached the equilibrium, even when long times of extraction (20 and 24 h) were evaluated. SPME–DED appears to be a rapid and suitable technique for extracting NA from model food system at both refrigeration and room temperatures.     

Extraction and characterisation of pectin methylesterase from black carrot (Daucus carota L.)

This study was carried out to determine some of the biochemical properties of pectin methylesterase (PME) from black carrot. The enzyme showed very high activity in a broad pH range of 6.5–8.5, with the optimum pH occurring at 7.5. The optimum temperature for maximal PME activity was found to be 55 °C. NaCl enhanced PME activity, particularly at 0.2 M. K_m and V_max values for black carrot PME using apple pectin as substrate were found to be 2.14 mg/ml (r² = 0.988) and 3.75 units/ml, respectively. The enzyme was stable between the temperatures of 30–50 °C/5 min whereas it lost nearly all of its activity at 70 °C/5 min. E_a and Z values were found to be 196.8 kJmol⁻¹ (r² = 0.996) and 2.16 °C (r² = 0.995), respectively.     

Preparation and antihypertensive activity of peptides from Porphyra yezoensis

This research was to develop a antihypertensive peptide, an efficient angiotensin converting enzyme (ACE) inhibitor (ACEI), from Porphyra yezoensis. Seven commercial enzymes were screened and then enzymatic hydrolysis conditions were optimised. The results showed that alcalase was the most effective for hydrolysis and its optimum conditions for achieving the highest antihypertensive activity of peptide were 1.5% substrate, 5% alcalase, pH 9.0, and temperature of 50 °C at a hydrolysis time of 60 min. The antihypertensive peptide produced under the optimum conditions had a high ACE inhibition rate of 55.0% and a low IC₅₀ value of 1.6 g/l and remained at high stability at temperatures of 4, 25, and 37 °C, pH values of 2.0 and 8.0, and after pepsin and trypsin treatments. Major proteins from P. yezoensis were glutelin, albumin, and gliadin. The albumin and glutelin had higher hydrolysis rates than the gliadin, but the IC₅₀ value of glutelin was the lowest, which indicated that the antihypertensive peptide from glutelin was more functional.     

Release kinetics of nisin from biodegradable poly(butylene adipate-co-terephthalate) films into water

The release kinetics of nisin from poly(butylene adipate-co-terephthalate) (PBAT) to distilled water was studied at of 5.6, 22 and 40 °C. The release kinetics of nisin from PBAT film was described using Fick’s second law of diffusion, partition coefficient, and Weibull model. The diffusion coefficients (D) determined were 0.93, 2.29, and 5.78 × 10⁻¹⁰ cm²/s at 5.6, 22, and 40 °C, respectively. The partition coefficients (K) calculated were 0.84, 3.89, and 5.2 × 10³ at 5.6, 22, and 40 °C, respectively. The nisin release data at selected temperatures were fitted with the Weibull model (R² > 0.97) with b and n values ranging from 0.02 to 0.98 and from 0.28 to 0.45, respectively. The temperature dependence of D, K, and Weibull model parameter b was modeled using the Arrhenius equation giving values of activation energy (E_a) of 38.3 kJ mol⁻¹ (for D), 38.5 kJ mol⁻¹ (for K), and 79.5 kJ mol⁻¹ (for b).     

Effect of thermal treatment on whey protein polymerization by transglutaminase: Implications for functionality in processed dairy foods

The effect of thermal treatment of whey proteins (50 g/100 g) at 75, 80, 85, 90 and 95 ^°C before enzymatic treatment with microbial transglutaminase was evaluated by rheological measurements. Thermal denaturation of whey proteins was determined by differential scanning calorimetry (DSC); and the gel point and turbidity were also evaluated after addition of transglutaminase at different pH values in protein solutions. A significant (p < 0.05) interaction was observed between transglutaminase and thermal treatments. At temperatures higher than 85 ^°C the apparent viscosity measurements of whey protein solutions with transglutaminase were significantly higher than those of the control samples. DSC analysis showed that thermal denaturation occurred at temperatures close to 82 ^°C, and the enzymatic reaction was enhanced at higher temperatures. The gel point of whey proteins decreased with transglutaminase addition. This decrease became greater as a function of reaction time due to the formation of high weight protein polymers catalyzed by transglutaminase, which was also observed in the turbidity analysis.     

Artificial intelligence in predicting extraction of anti-cancer compounds

Saponins from the particulate Saponaria vaccaria L. seeds (0.29–0.84 mm, 15.35–61.40 g H₂O/100 g dry mass) were extracted for methanol concentrations (MeOH) of 30, 50, 70, and 90 mL/100 mL H₂O and temperatures (T) of, 30, 45, and 60 °C at ten extraction intervals (t) between 1 and 180 min. A calibration equation was developed from the liquid-chromatogram–mass spectroscopy peaks to quantify the extract yields (mg mL⁻¹) for various types of saponins. An artificial neural network (ANN) with three inputs, MeOH, T, and t predicted the extraction kinetics and the yields with less than ca. 12% error. The ANN model not only slightly outperformed the numerical diffusional model, but it also made the prediction simple and faster eliminating the use of the partition coefficient and the effective diffusivity. Therefore an ANN model can be a right approach to predict the yields of saponins and similar products.     

Kinetics of ascorbic acid degradation in fruit-based infant foods during storage

The kinetics of ascorbic acid (AA) degradation in a fruit-based beikost product added with AA were determined after storage at 4, 25, 37 and 50 °C during 4, 8, 12, 16 and 32 weeks in plastic polypropylene/ethylene–vinyl alcohol vacuum packaging. It was confirmed that AA degradation followed an Arrhenius first-order kinetics, with an activation energy of 20.11 ± 0.33 kcal mol⁻¹. No AA losses at 4 °C were recorded during the entire storage period. In contrast, a time- and temperature-dependent decrease (p < 0.05) in AA was observed at the other tested temperatures – the degradation rate decreasing from 50 °C to 25 °C, as expected. AA percentage retention at the end of storage ranged between 6.4% (50 °C/16 weeks) and 100.9% (4 °C/32 weeks).     

Modelling the effect of water immersion thermal processing on polyacetylene levels and instrumental colour of carrot disks

C₁₇ polyacetylenes are a group of bioactive compounds present in carrots which have recently gained scientific attention due to their cytotoxicity against cancer cells. In common with many bioactive compounds, their levels may be influenced by thermal processes, such as boiling or water immersion. This study investigated the effect of a number of water immersion time/temperature combinations on concentrations of these compounds and attempted to model the changes. Carrot samples were thermally treated by heating in water at temperatures from 50–100 °C and holding times of 2–60 min. Following heating, levels of falcarinol (FaOH), falcarindiol (FaDOH), falcarindiol-3-acetate (FaDOAc) and Hunter colour parameters (L^∗, a^∗, b^∗) were determined. FaOH, FaDOH, FaDOAc levels were significantly reduced at lower temperatures (50–60 °C). In contrast, samples heated at temperatures from 70–100 °C exhibited higher levels of polyacetylenes (p < 0.05) than did raw unprocessed samples. Regression modelling was used to model the effects of temperature and holding time on the levels of the variables measured. Temperature treatment and holding time were found to significantly affect the polyacetylene content of carrot disks. Predicted models were found to be significant (p < 0.05) with high coefficients of determination (R²).     

Moisture sorption properties of chitosan

The moisture equilibrium isotherms of chitosan were determined at 20, 30, 40, 50 and 60 °C, using the gravimetric static method. Experimental data were analyzed by the GAB, Oswin, Halsey and Smith equations. Isosteric heat and differential entropy of sorption were determined from the GAB model using the Clausius-Clapeyron and Gibbs-Helmholtz equations, and pore size distribution was calculated by the Kelvin and Halsey equations. The GAB and Oswin equations showed best fit to the experimental data with R² ≈ 99% and low mean relative deviation values (E% < 10%). Monolayer moisture content values (from 0.12 to 0.20 kg kg⁻¹) and water surface area values (from 450 to 700 m² g⁻¹) decrease with increasing temperature. Isosteric heat and differential entropy of sorption were estimated as a function of moisture content. The Kelvin and Halsey equations were adequate for calculation of pore size distribution, which varied from 0.5 to 30 nm.     

Water uptake and its impact on the texture of lentils (Lens culinaris)

Water uptake behavior of three cultivars of lentils (Boomer, French-green and Nugget) was studied at three different hydration temperature regimes (room temperature, 50 °C and 85 °C). Boomer had the highest amount of water uptake capacity (74.60 g water/100 g of seeds) at room temperature (20 °C) which can be linked with its pore properties. French-green lentils imbibed the largest amount of water at elevated soaking temperatures (50 °C and 85 °C) and can be attributed to its higher seed surface area to volume ratio, high protein content and relatively thinner seed coat. Water uptake at elevated temperatures (50 °C and 85 °C) were predicted by a two parameter Mitscherlich model (R² > 0.99, χ² < 0.5) within 1.36–3.07% average absolute error. At room temperature, only the water uptake of Boomer was reasonably predicted by this model. The texture (hardness) of the soaked lentils was found to be related the amount of water uptake and soaking temperature used rather than seed size or seed mass alone. The hardness values of Boomer, French-green and Nugget at 85 °C after 75 min soaking were reduced to 5.66%, 3.53% and 6.77%, respectively compared to their respective initial seed hardness values. The water uptake capacity of the aged Boomer was found to be significantly reduced compared to the fresh seeds (p < 0.01) while French-green and Nugget do not exhibit significant change (p < 0.05). During 72 h of germination, hardness of all lentil cultivars showed a typical pattern which decreased in the first 24 h followed by an increase compared to the hydrated seeds. A peak hardness value was obtained within 36–48 h before finally declining in all types of lentils. Structural changes within the cotyledon, such as depletion of starch granules, new nuclei formation and development of tissues in vascular bundles and rupture of the seed coat were observed during germination.     

Design and characterisation of an enzyme system for inulin hydrolysis

The optimal conditions for inulin hydrolysis using a commercial inulinase preparation, either free or immobilised in activated Amberlite were established by factorial design and surface response methodology. The immobilised biocatalyst displayed highest activity at pH 5.5 and 50 °C, whereas the optimum pH for the free form was slightly more acidic (4.5), and the optimum temperature was a little higher (55 °C). The model system estimated optimal pH and temperature values of 5.4 and 52 °C for the immobilised system and 4.9 and 56 °C for the free system. Michaelis–Menten type kinetics adequately described both free and immobilised bioconversion systems, which were evaluated under the respective optimal pH and temperature conditions. The use of a non-linear regression method for the determination of the kinetic parameters provided a best fit to the experimental data, as compared to a conventional Lineweaver–Burk linearisation. The K_m for inulin of the free biocatalyst was 153 g l⁻¹ at 55 °C and pH 4.5, whereas the apparent K_m for inulin of the immobilised biocatalyst was 108 g l⁻¹ at pH 5.5 and 50 °C. The reutilisation of the immobilised biocatalyst throughout consecutive batches was evaluated. A significant decrease of enzyme activity was observed in the first two batches, after which the system exhibited significant stability. The low cost of the support, the stability of the immobilised biocatalyst towards pH and temperature and its high affinity for the substrate suggests its potential for inulin hydrolysis.     

Effects of light,temperature and water activity on the kinetics of lipoxidation in almond-based products

Lipoxidation in almond-derived products was investigated using the chemiluminescence (CL) and thiobarbituric acid-reactive substances (TBARS) methods to detect the first and later reaction products, respectively. The effects of light during storage at 5 °C, 22 °C and 40 °C were studied, as well as the effects of combined heat/water activity treatments in the 60–120 °C and 0.38–0.72 range. During storage, light was found to enhance the CL and TBARS values, and specific responses were observed in almond paste and the final Calisson product. During the heating of almond paste, as the initial water activity (a_w) increased, the CL rate constants increased during heating to 60 °C and 80 °C, but interestingly, these values decreased during further heating to 120 °C, whereas the maximum TBARS rate constants occurred at a_w 0.57 at all the heating temperatures tested. The activation energies, based on the CL and TBARS values, decreased specifically when the a_w increased from 0.38 to 0.72, giving overall values ranging from110 kJ mol⁻¹ to 60 kJ mol⁻¹. Likewise, in the same water activity range, the temperature-dependent rate constant enhancing factor (Q₁₀) decreased from 3.3 to 1.6.     

Properties of polyphenol oxidase from Anamur banana (Musa cavendishii)

Polyphenol oxidase (PPO) was extracted from Anamur banana, grown in Turkey, and its characteristics were studied. The optimum temperature for banana PPO activity was found to be 30 °C. The pH-activity optimum was 7.0. From the thermal inactivation studies, in the range 60–75 °C, the half-life values of the enzyme ranged from 7.3 to 85.6 min. The activation energy (E_a) and Z values were calculated to be 155 kJ mol⁻¹ and 14.2 °C, respectively. K_m and V_max values were 8.5 mM and 0.754 OD₄₁₀ min⁻¹, respectively. Of the inhibitors tested, ascorbic acid and sodium metabisulphite were the most effective.     

Pacific whiting (Merluccius productus) underutilization in the Gulf of California: Muscle autolytic activity characterization

In México’s Northwest coast, Pacific whiting (Merluccius productus) is considered an under-utilized species because of its high tendency to become parasitized, thus promoting a high proteolytic activity present in muscle tissue. Sample fish for study were separated in lots by degree of parasitism in “apparent” parasitized (APP) and advanced parasitized (ADP). Thus, pH and temperature conditions of mayor endogenous proteolytic activity in muscle were determined. Maximum activity was detected at 50 °C (pH 3.5–4.0) and at 60 °C (pH 6.75–7.0). Parasitism degree had a significant effect in enzyme activity at acidic pH (p < 0.05) being higher in APP at low temperature (30 °C). Higher temperatures (40–50 °C) favored (p < 0.05) activity in ADP muscle (same pH range) with the highest (p < 0.05) observed at 50 °C at pH 3.5. No much difference was observed at pH 7.0–8.0. Results suggest that pH around physiological conditions at 60 °C could be used as an advantage in fish protein hydrolysate production or as processing aid where a protein hydrolysis is required.     

Cooking quality of faba bean after storage at high temperature and the role of lignins and other phenolics in bean hardening

Selected physical and chemical characteristics of faba beans (Vicia faba L.) cv. Fiesta were studied after 12 months storage at 5, 15, 25, 37, 45 or 50 °C (±2 °C) in relation to the hard-to-cook phenomenon. In comparison with control (seeds stored at 5 °C), seeds stored at 15 and 25 °C demonstrated non-significant (p?0.05) changes in most of the physical and chemical characteristics including hydration and swelling coefficients, acid detergent fibre, lignin and tannin contents, whereas seeds stored at ?37 °C demonstrated significant changes (p?0.05). Solutes and electrolytes leaching after 18 h soaking substantially increased with increased temperature. Faba bean hardness tested by the hard-to-cook test also increased substantially with increased storage temperature. After 8 h soaking followed by 2 h cooking, the puncture force required for seeds stored at 5 °C was 3.3 N seed⁻¹ whereas seeds stored at 50 °C required a much higher puncture force of 15.2 N seed⁻¹. There was a high negative correlation (r²=0.98) between storage temperature and cooking ability of faba bean. Substantial increases in acid detergent fibre and lignin contents occurred with increased storage temperatures. There was a three-fold increase in lignin content of faba bean stored at 50 °C compared to those stored at 5 °C and it was correlated with bean hardness (r²=0.98). Storage at high temperatures for 12 months led to a substantial reduction in total free phenolics especially in the testa and there was a greater reduction with increasing storage temperature. Reduction in free phenolics was negatively correlated (r²=0.75) with bean hardness.     

Are virgin olive oils obtained below 27 °C better than those produced at higher temperatures?

Within the European Union, indications of ‘first cold pressing’ and ‘cold extraction’ can only be used for virgin olive oil (VOO) obtained below 27 °C from mechanical processing. Three different malaxing temperatures (25, 35 and 45 °C) are here evaluated for the quality of the VOO obtained in a continuous industrial plant. The oils were stored at room temperature in the dark for 12 months. Initially, oil obtained from a blend of Frantoio/Leccino cultivars (F/L) had higher acidity and peroxide levels and lower phenolic content than a Coratina cultivar (Cor). The oxidative stability of the oils positively correlated with malaxation temperature (F/L, R² = 0.818; Cor, R² = 0.987) as the phenolic content was directly proportional to the temperature (F/L, R² = 0.887; Cor, R² = 0.992). Only oils obtained at 45 °C were rejected because of ‘heated or burnt’ off-flavour. Decarboxymethylation of secoiridoids and further hydrolysis of phenolic esters occurred during storage. The oxidation products of derivatives of tyrosol and hydroxytyrosol were detected after nine months in both the F/L and Cor samples. Thus, VOO obtained at a processing temperature lower than 27 °C does not show higher chemical and sensory qualities than VOO obtained at 35 °C.     

Evaluation of a static treatment chamber to investigate kinetics of microbial inactivation by pulsed electric fields at different temperatures at quasi-isothermal conditions

A static parallel electrode treatment chamber with tempered electrodes has been designed to obtain kinetics data on microbial inactivation by pulsed electric fields (PEF) at different temperatures at quasi-isothermal conditions. Distribution of the electric field strength and temperature within the treatment zone was estimated by a finite element method. A good agreement was observed between the temperatures estimated by numerical simulation and temperatures measured by a thermocouple in the treatment zone before and after the PEF treatments (values of RMSE below 3%). Influence of the treatment temperature on PEF inactivation (30 kV/cm) of Salmonella typhimurium was investigated at temperatures between 4 and 50 °C in media of pH 3.5 and 7.0. Treatment temperature had an important effect on microbial inactivation for both values of pH. At pH 3.5 the inactivation of S. typhimurium was irrelevant at 4 °C but about 1.5, 2.9, 4.0 and 5.0 Log₁₀ reductions were obtained after 30 pulses (90 μs) at 15, 27, 38 and 50 °C, respectively. At pH 7.0, around two Log₁₀ cycles of inactivation were observed after 50 pulses (150 μs) at 4 °C. At temperatures in the range between 15 and 50 °C the treatment temperature practically did not influence PEF resistance of S. typhimurium. A model based on the Weibull distribution adequately described kinetics of inactivation of S. typhimurium at different temperatures. The treatment chamber designed in the investigation could be useful to obtain kinetics data on PEF destruction of microorganisms or other components of interest at a uniform distribution of electric field strength and homogeneous and quasi-isothermal conditions in a wide range of temperatures.     

High-pressure destruction kinetics of Clostridium sporogenes ATCC 11437 spores in milk at elevated quasi-isothermal conditions

The high-pressure sterilization establishment requires data on isobaric and isothermal destruction kinetics of baro-resistant pathogenic and spoilage bacterial spores. In this study, Clostridium sporogenes 11437 spores (10⁷ CFU/ml) inoculated in milk were subjected to different pressure, temperature and time (P, T, t) combination treatments (700–900 MPa; 80–100 °C; 0–32 min). An insulated chamber was used to enclose the test samples during the treatment for maintaining isobaric and quasi-isothermal processing conditions. Decimal reduction times (D values) and pressure and temperature sensitivity parameters, Z_T (pressure constant) and Z_P (temperature constant) were evaluated using a 3 × 3 full factorial experimental design. HP treatments generally demonstrated a minor pressure pulse effect (PE) (no holding time) and the pressure hold time effect was well described by the first order model (R² > 0.90). Higher pressures and higher temperatures resulted in a higher destruction rate and a higher microbial count reduction. At 900 MPa, the temperature corrected D values were 9.1, 3.8, 0.73 min at 80, 90, 100 °C, respectively. The thermal treatment at 0.1 MPa resulted in D values 833, 65.8, 26.3, 6.0 min at 80, 90, 95, 100 °C respectively. By comparison, HP processing resulted in a strong enhancement of spore destruction at all temperatures. Temperature corrected Z_T values were 16.5, 16.9, 18.2 °C at 700, 800, 900 MPa, respectively, which were higher than the thermal z value 9.6 °C. Hence, the spores had lower temperature sensitivity at elevated pressures. Similarly, corrected Z_P values were 714, 588, 1250 MPa at 80, 90, 100 °C, respectively, which illustrated lower pressure sensitivity at higher temperatures. By general comparison, it was concluded that within the range operating conditions employed, the spores were relatively more sensitive to temperature than to pressure.     

Temperature-dependent diffusion coefficient of oil from different sunflower seeds during extraction with hexane

Oil extraction from confectionery, oilseed and wild sunflower seeds with n-hexane was investigated by laboratory tests carried out in a stirred batch extractor at several temperatures (40, 50 and 60 °C). The rates of extraction were determined from ground sunflower seeds (particle sizes between 0.420 and 1.000 mm). The oil yield in the extract increased with higher contact time and extraction temperature in all the cases. Equilibrium constants at 50 °C for different solvent-ground seed ratios are reported. A mathematical model of oil extraction from seeds of sunflowers, based on a modified diffusive process in spherical geometry of particles, was proposed. The analysis of significance of the coefficient of fitting regression models showed significant differences between temperatures for each genotype and between genotypes at each temperature. The resulting diffusion coefficient ranged from 1.34 × 10⁻¹² to 1.87 × 10⁻¹² m²/s for confectionery, 2.06 × 10⁻¹² to 5.03 × 10⁻¹² m²/s for oilseed, and 9.06 × 10⁻¹³ to 1.18 × 10⁻¹² m²/s for wild sunflower. The temperature dependence of the diffusion coefficient was represented by an Arrhenius-type equation for each sunflower seed studied. Activation energy values of 13.74, 33.95 and 11.32 kJ/mol were obtained for confectionery, oilseed and wild sunflower, respectively.