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1.
《LWT》2004,37(2):171-175
The degradation of ascorbic acid was studied in mushrooms heated at temperatures between 110 and 140°C, high-temperature short-time conditions, in a five-channel computer-controlled thermoresistometer. The kinetics parameters were calculated on the assumption that there are 2 degradation mechanisms, one aerobic (during the first few seconds of the process) and the other anaerobic. The 2 stages followed first-order reaction kinetics, with Ea=46.36 kJ/mol for aerobic degradation and Ea=49.57 kJ/mol for anaerobic degradation. 相似文献
2.
The kinetics of tocols degradation in wholemeal and white flours from einkorn cv Monlis and bread wheat cv Serio were studied during storage at five different temperatures (−20, 5, 20, 30 and 38 °C) up to 242 days. Tocols decreased as a function of time and temperature, following first-order kinetics. Degradation rates and their dependence upon temperature were similar for the two Triticum species studied. Tocols decrease was quicker in white flour than in wholemeal flour (on average for total tocols at 38 °C, k = 7.79 × 10−3 days−1 vs 3.15 × 10−3 days−1, respectively). The temperature-dependent degradation was similar for all homologues (Ea = 34.3–49.4 kJ/mol) except for α-T, less thermostable in white flours (Ea = 61.2 kJ/mol in einkorn and Ea = 54.7 kJ/mol in bread wheat). 相似文献
3.
Meadowsweet was extracted in water at a range of temperatures (60–100 °C), and the total phenols, tannins, quercetin, salicylic acid content and colour were analysed. The extraction of total phenols followed pseudo first-order kinetics, the rate constant (k) increased from 0.09 ± 0.02 min−1 to 0.44 ± 0.09 min−1, as the temperature increased from 60 to 100 °C. An increase in temperature from 60 to 100 °C increased the concentration of total phenols extracted from 39 ± 2 to 63 ± 3 mg g−1 gallic acid equivalents, although it did not significantly affect the proportion of tannin and non-tannin fractions. The extraction of quercetin and salicyclic acid from meadowsweet also followed pseudo first-order kinetics, the rate constant of both compounds increasing with an increase in temperature up until 90 °C. Therefore, the aqueous extraction of meadowsweet at temperatures at or above 90 °C for 15 min yields extracts high in phenols, which may be added to beverages. 相似文献
4.
Polyphenol oxidase (PPO) of Vanilla planifolia Andrews beans was extracted and purified through ammonium sulphate precipitation, dialysis, and gel filtration chromatography. PPO activity was measured by improved UV technique using 4-methylcatechol and catechol as substrates increasing substantial sensitivity of previous procedure. The optimum pH and temperature for PPO activity were found to be 3.0 and 3.4 and 37 °C, respectively. Km and Vmax values were found to be 10.6 mM/L and 13.9 OD300 min−1 for 4-methylcatechol and 85 mM/L and 107.2 OD300 min−1 for catechol. In an inhibition test, the most potent inhibitor was found to be 4-hexylresorcinol followed by ascorbic acid. The thermal inactivation curve was biphasic. Activation energy (Ea) and z values were calculated as 92.10 kJ mol−1 and 21 °C, respectively. 相似文献
5.
The kinetic parameters of surface color degradation of canned fresh green peas sterilized in a rotary retort, using the a* value from a spectrophotometer as the physical parameter and the concept of fractional conversion in conditions of unsteady state were determined in the range of retort temperatures of 120 and 131 °C. Experimental initial a* values fluctuated between −14.4 and −15.7, while final a* values ranged between −0.165 and −4.75. After five iterations performed, solving simultaneously the energy balance of the system, the differential equation of unsteady conduction for spheres and the first-order degradation reaction of surface color by numerical methods, the best values of k100 °C and Ea determined were 5.48×10−4 s−1 and 89.37 kJ/mol respectively, being 5.68% the deviation between experimental and predicted fractional retentions of a* with the determined parameters. 相似文献
6.
Weibull distribution for modeling air drying of coroba slices 总被引:2,自引:0,他引:2
Application of Weibull distribution model was investigated for describing the moisture content of coroba slices during air drying. One set of experiments was performed following a full factorial design at three levels for air temperature (71, 82 and 93 °C) and velocity (0.82, 1.00 and 1.18 m/s). The set was designed to assess the adequacy of the Weibull model to describe water losses. The high regression coefficients (R2 > 0.99) and low reduced chi-square indicated the acceptability of Weibull model for predicting moisture content. Values of scale parameter ranged from 41.77 to 71.52 (min) and values of shape parameter ranged from 1.06 to 1.21. Temperature sensitivity of scale parameter increased with increasing air velocity from 0.82 m/s (Ea = 210.45 J/mol) to 1.00 m/s (Ea = 214.93 J/mol) and then decreased with increasing velocity to 1.18 m/s (Ea = 139.03 J/mol). The normalized Weibull model was investigated for determining the effective diffusion coefficient (De). The De values ranged approximately from 2.51 × 10−12 m2/s to 4.27 × 10−12 m2/s. 相似文献
7.
In this study, the effects of two blanching conditions on ascorbic acid (AA) and peroxidase (POD) in different segments of asparagus (bud, upper, middle, and butt) were investigated. The blanching treatments were: blanching in water at 70, 80 and 90 °C (WB); microwave heating (900 W, 30 s) followed by water blanching (MW + WB). AA degradation and POD inactivation in all segments of asparagus for both treatments are well described by first-order models. The degradation rate of AA and POD is gradually increased from butt to bud segment of asparagus. In addition, MW pre-treatment could increase the Ea of AA degradation and decrease the Ea of POD inactivation during water blanching of asparagus. Therefore, it is recommended that the different segments of asparagus should be subjected to different blanching times, and MW pre-treatment could be applied for alleviating AA degradation and accelerating POD inactivation during blanching, cooking and pasteurisation in water. 相似文献
8.
M. Ümit Ünal 《Food chemistry》2007,100(3):909-913
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 (Ea) and Z values were calculated to be 155 kJ mol−1 and 14.2 °C, respectively. Km and Vmax 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. 相似文献
9.
Ascorbic acid degradation kinetics of sonicated orange juice during storage and comparison with thermally pasteurised juice 总被引:3,自引:0,他引:3
Ascorbic acid degradation kinetics of sonicated orange juice during storage were determined and compared to thermally pasteurised samples. Acoustic energy densities (AED) ranging from 0.30 to 0.81 W/mL and treatment times of 2-10 min were investigated. The degradation kinetics of sonicated samples followed first-order kinetics (R2 ≥ 0.91) during processing. During storage ascorbic acid degradation of sonicated samples followed the Weibull model (R2 ≥ 0.97) with β values ranging from 0.662 to 0.697. Comparatively, first-order degradation kinetics were observed during storage for thermally pasteurised (R2 = 0.98) and control samples (R2 = 0.96). Increased shelf life based on ascorbic acid retention was found for sonicated samples compared to thermally pasteurised samples. Predicted shelf life for sonicated orange juice ranged from 27 to 33 days compared to 19 days for thermally pasteurised juice during storage at 10 °C. These results indicate that sonication results in enhanced retention of ascorbic acid in orange juice during storage compared to thermal processing. 相似文献
10.
The water effective diffusion coefficient of sardine sheets during vacuum pulse osmotic dehydration was determined. Sardine sheets (20.1×15.0×6.4 mm3) were osmotic dehydrated at brine concentrations between 0.15 and 0.27 g NaCl/g, and temperatures between 32 and 38 °C. The water effective diffusion coefficient ranged approximately from 1.46×10−10 m2/s to 2.41×10−10 m2/s. In general, diffusion coefficient increased with increasing concentration and temperature. Dependence on temperature followed an Arrhenius relationship, regardless of concentration Diffusion coefficient at 0.18 g NaCl/g was found to be the most temperature sensitive (Ea=39.62 kJ/mol) while that at 0.15 g NaCl/g was the least temperature sensitive (Ea=23.67 kJ/mol). The water effective diffusion coefficient was empirically correlated with concentration and temperature of osmotic solution. A high degree of correlation was observed between predicted and experimental values of the water effective diffusion coefficient (R2=0.856). 相似文献
11.
The knowledge on thermal inactivation of biopreservatives in a food matrix is essential to allow their proper utilisation in food industry, enabling the reduction of heating times and optimisation of heating temperatures. In this work, thermal inactivation of the antimicrobial peptide P34 in skimmed and fat milk was kinetically investigated within the temperature range of 90–120 °C. The inactivation kinetic follows a first-order reaction with k-values between 0.071 and 0.007 min−1 in skimmed milk, and 0.1346 and 0.0119 min−1 in fat milk. At high temperatures, peptide P34 was less resistant in fat milk, with a significant decrease in residual activity as compared with skimmed milk. At temperatures below 110 °C, the fat globules seem to have protective effect to the peptide P34. Results suggest that peptide P34 is heat stable in milk with activation energy of 90 kJ mol−1 in skimmed milk and 136 kJ mol−1 in fat milk. 相似文献
12.
Polyphenol oxidase (PPO) was isolated from Victoria grapes (Vitis vinifera ssp. Sativa) grown in South Africa and its biochemical characteristics were studied. Optimum pH and temperature for grape PPO activity were pH 5.0 and T = 25 °C with 10 mM catechol in McIlvaine buffer as substrate. PPO showed activity using the following substances: catechol, 4 methyl catechol, d, l-DOPA, (+) catechin and chlorogenic acid. Km and Vmax values were 52.6 ± 0.00436 mM and 653 ± 24.0 OD400 nm/min in the case of 10 mM catechol as a substrate. Eight inhibitors were tested in this study and the most effective inhibitors were found to be ascorbic acid, l-cysteine and sodium metabisulfite. Kinetic studies showed that the thermal inactivation of Victoria grape PPO followed first-order kinetics, with an activation energy, Ea = 225 ± 13.5 of kJ/mol. Both in semipurified extract and in grape juice, PPO showed a pronounced high pressure stability. 相似文献
13.
María E. LatorrePablo R. Bonelli Ana M. RojasLia N. Gerschenson 《Journal of food engineering》2012,109(4):676-684
The inactivation of polyphenoloxidase (PPO) and peroxidase (POX) in red beet by traditional and microwave (MW) blanching was studied. Microwave heating effects on color and texture were also studied.Red beet subjected to MW blanching for 5 min at 100-200 W resulted in large weight losses accompanied by a high degree of shrinking. POX was the more heat resistant enzyme. The 90% destruction (D value) of the activity of both enzymes could be achieved only at 200 W within the 5 min frame employed for the tests.When the samples were immersed in water and both the food sample and the water were submitted to MW exposure at 250-450 W or variable power with a maximum at 935 W, shrinking was avoided. The D value at 90 °C (reference; DTref) and z could be determined after time-temperature corrections, and it was observed that, in general, DTref values for POX were smaller than for PPO. The microwave treatment (maximum power: 935 W) designed to provide a similar temperature profile to the one observed for traditional blanching (immersion in water at 90 °C), showed the smallest DTref value for POX inactivation. All treatments reduced elastic characteristics and changed the color of the tissues showing a shift to blue mainly in the case of microwave processes. 相似文献
14.
The kinetics of the formation of radicals in meat by high pressure processing (HPP) has been described for the first time. A threshold for the radicals to form at 400 MPa at 25 °C and at 500 MPa at 5 °C has been found. Above this threshold, an increased formation of radicals was observed with increasing pressure (400–800 MPa), temperature (5–40 °C) and time (0–60 min). The volume of activation (ΔV#) was found to have the value −17 ml mol−1. The energy of activation (Ea) was calculated to be 25–29 kJ mol−1 within the pressure range (500–800 MPa) indicating high independence on the temperature at high pressures whereas the reaction was strongly dependent at atmospheric pressure (Ea = 181 kJ mol−1). According to the effect of the processing conditions on the reaction rate, three groups of increasing order of radical formation were established: (1) 55 °C at 0.1 MPa, (2) 500 and 600 MPa at 25 °C and 65 °C at 0.1 MPa, and (3) 700 MPa at 25 °C and 75 °C at 0.1 MPa. The implication of the formation of radicals as initiators of lipid oxidation under HPP is discussed. 相似文献
15.
A mathematical model is proposed to simulate the process of drying of individual pieces of red pepper under constant external conditions and to predict changes in some nutritional and organoleptic attributes of the product. The model was solved numerically to obtain moisture content and temperature as well as ascorbic acid and carotenoids concentration in the product as a function of time. A good agreement between predictions and experimental data at different drying temperatures was obtained.Water sorption isotherms of red pepper were determined in the range 20-50 °C and represented by two different sorption equations. Drying kinetics were represented by a diffusive model, the effective moisture diffusivity ranging from 5.01 to 8.32×10−10 m2/s with an activation energy of 23.35 kJ/mol. Degradation kinetics for ascorbic acid and total carotenoids were measured in the range 50-70 °C and modelled as first-order reactions. The rate constants increased with temperature and product moisture content. Average activation energies for carotenoids and vitamin C degradation were 50.1 and 26.9 kJ/mol, respectively. 相似文献
16.
In this study, chitosan beads were prepared by using a cross-linking agent and the resulting beads were employed in immobilization process. Studies on free and immobilized pepsin systems for determination of optimum temperature, optimum pH, thermal stability, pH stability, operational stability, storage stability and kinetic parameters were carried out. The optimum temperature interval for free pepsin and immobilized pepsin were 30–40 and 40–50 °C, respectively. Free and immobilized pepsin showed higher activity at pH 2.0–4.0. Apparent Km = 12.0 g L−1 haemoglobin (1.56 mM tyrosine) and Vmax = 5220 μmol (mg protein min)−1 values were obtained for free pepsin, while apparent Km = 20.0 g L−1 haemoglobin (2.16 mM tyrosine) and Vmax = 2780 μmol (mg protein min)−1 values were obtained for immobilized pepsin. Thermal stability and storage stability of immobilized pepsin were higher than that of free pepsin. Milk clotting activity was used for evaluation of the applicability of pepsin immobilization to industrial process. Optimum milk clotting temperature was found as 40 °C for free pepsin and 50 °C for immobilized pepsin. 相似文献
17.
Drying of cape gooseberry fruits is a slow process because of the low permeability to moisture of the fruit’s waxy skin. In this work, the effect of chemical pretreatments (sunflower oil/K2CO3 or olive oil/K2CO3 at 28 °C, and NaOH/olive oil at 96 °C) and physical pretreatments (blanching) to break down the waxy surface and accelerate moisture diffusion during drying, was assessed. Drying was carried out at 60 °C and 2 m/s air velocity for 10 h. The lowest moisture content (0.27 kg water/kg db), the highest vitamin C content (0.36 mg/g), and the greatest rehydration capacity (1.89) were obtained in fruits pretreated with olive oil (9.48%) and K2CO3 (4.74%). However, the greatest changes in color (ΔE* = 15.05) and chroma (ΔC* = 9.03) were also associated to fruits pretreated with olive oil and K2CO3. The effective diffusivity of water during drying was 7.37 × 10−11 m2/s in pretreated samples compared with 6.61×10−11 m2/s for untreated samples. 相似文献
18.
Inactivation kinetics of peroxidase and polyphenol oxidase in fresh Rabdosia serra leaf were determined by hot water and steam blanching. Activation energy (52.30 kJ mol−1) of polyphenol oxidase inactivation was higher than that (20.15 kJ mol−1) of peroxidase. Water blanching at 90 °C or steam blanching at 100 °C for 90 s was recommended as the preliminary treatment for the retention of phenolics. Moreover, comparative evaluation of drying methods on the phenolics profiles and bioactivities of R. serra leaf were conducted. The results indicated that only intact leaf after freeze drying retained the initial quality. The sun- and air-dried leaves possessed identical phenolic profiles. The homogenised leaf (after freeze-drying) possessed a lower level of phenolics due to enzymatic degradation. Good antioxidant activities were detected for the sun- and air-dried leaves. There was insignificant difference in anti-tyrosinase and anti-α-glucosidase activities among sun-, air-, and freeze-dried leaves. 相似文献
19.
Kinetic characterisation and thermal inactivation study of polyphenol oxidase and peroxidase from table grape (Crimson Seedless) 总被引:1,自引:0,他引:1
Polyphenol oxidase (PPO) and peroxidase (POD) were extracted from a table grape (Crimson Seedless) using Triton X-114 and characterized using spectrophotometric methods. Both PPO and POD were activated by acid shock. However, in the presence of the anionic detergent sodium dodecil sulphate (SDS), PPO was activated whereas POD was inactivated. The enzymes were kinetically characterized and both followed Michaelis–Menten kinetics, although with different values of their kinetic parameters. The Vm/Km ratio showed that Crimson Seedless grape PPO presents a similar affinity for 4-tert-butyl-catechol (TBC) whether activated by acid shock (0.018 min−1) or SDS (0.023 min−1). With regards to POD, the Km and Vm values for 2,2′-azinobis(3-ethylbenzothiazolinesulphonic acid) (ABTS) were 0.79 mM and 1.20 μM/min, respectively. In the case of H2O2, the Km and Vm value were 0.4 mM and 0.93 μM/min, respectively. PPO and POD showed similar thermostability, losing >90% of relative activity after only 5 min of incubation at 78 °C and 75 °C, respectively. In addition, PPO´s activation energy was similar to that obtained for POD (295.5 kJ/mol and 271.9 kJ/mol, respectively). 相似文献
20.
M. José Esteve A. Frígola L. Martorell Carmen Rodrigo 《Zeitschrift für Lebensmitteluntersuchung und -Forschung A》1999,208(2):144-147
Thermal degradation of green asparagus ascorbic acid in high-temperature short-time conditions was studied by heating in
a five-channel computer-controlled thermoresistometer. Ascorbic acid was heated to between 110 °C and 140 °C and the degradation
kinetics were analyzed assuming that two different inactivation mechanisms were occurring, one aerobic and the other anaerobic.
The two reactions followed first-order kinetics, with E
a=12.3(2.0) kcal/mol and k
125 °C=47.0(3.0)×10–3 s–1 for the aerobic oxidation, and E
a=6.1(1.4) kcal/mol and k
125 °C=4.1(0.2)×10–3 s–1 for the anaerobic degradation.
Received: 30 January 1998 / Revised version: 11 June 1998 相似文献