Kinetics of ascorbic acid degradation and colour change in ground cashew apples treated at high temperatures (100–180 °C)

Ascorbic acid (AA) degradation and colour changes, measured by the lightness index (L*), were determined in cashew apples (at low dissolved O₂ concentrations) heated at high temperature (100–180 °C) in a hermetically sealed cell. A nonisothermal method was developed to estimate thermal degradation kinetics. The results showed that reaction kinetics during heat treatments were well represented by first‐order reactions. The temperature dependence of the kinetic constants was described by an Arrhenius type equation. The activation energy (E_a) for AA degradation and lightness index were 94 ± 3 and 98 ± 3 kJ mol^?1, respectively. The reaction rate constant at 140 °C for AA degradation (64 × 10^?5 ± 3 × 10^?5 s^?1) was twice that for the lightness index change (33 × 10^?5 ± 2 × 10^?5 s^?1). Results allow generating temperature profiles of heat processes that would help preserve the AA of cashew apples as well as control the colour formation during high‐temperature processes.     

Kinetics of Thermal Degradation of the Anthocyanins Delphinidin-3-rutinoside and Malvidin-3-glucoside

The kinetics of the thermal degradation of the two anthocyanins delphinidin-3-rutinoside and malvidin-3-glucoside at 78, 88, 98 and 108 °C, depending on the pH and the type of solvent has been investigated. The first order reaction of delphinidin-3-rutinoside and malvidin-3-glucoside degradation has been established. The rate constants (K ± 10^?5s^?1), the activation parameters, factor Q₁₀ and the half-decay period have been calculated. The rate of delphinidin-3-rutinoside degradation is higher than that of malvidin-3-glucoside.     

Rheological behaviour and colour changes of ginger paste during storage

Ginger paste was prepared from fresh ginger by addition of 8% common salt and citric acid. The paste was thermally processed and packed in glass, polyethyleneterephthalate or high‐density‐polyethylene containers and stored at 5 ± 1 and 25 ± 1 °C for 120 days. The rheological characteristics of the paste were studied by using a computer controlled rotational viscometer over the temperature range of 20–80 °C. Samples were subjected to a programmed shear rate, increasing linearly from 0 to 200 s^?1 in 3 min, followed by a steady shear at 200 s^?1 for 3 min and finally decreasing linearly from 200 to 0 s^?1 in 3 min. Ginger paste exhibited pseudoplasticity with yield stress and flow adequately described by the Herschel–Bulkley model. The yield stress decreased exponentially with process temperature and ranged between 3.86 and 27.82 Pa. The flow behaviour index (n) varied between 0.66 and 0.82 over the temperature range. Both consistency index and apparent viscosity decreased with increase in temperature and the process activation energies were found to be in the range of 16.7 to 21.9 kJ mol^?1. The effect of temperature was significant (P < 0.05) on the Hunter colour combination value of the paste during storage; however it was not affected by type of packaging material (P > 0.05). It is recommended that ginger paste is stored at 5 ± 1 °C in polyethyleneterephthalate or glass containers.     

Effect of drying kinetics on main bioactive compounds and antioxidant activity of acerola (Malpighia emarginata D.C.) residue

This study investigates the drying kinetics of residue of acerola, in a fixed‐bed dryer, analysing the effect of the process variables on the antioxidant properties of the residue. A complete factorial design 3² has been performed, where the independent variables studied were as follows: air velocity (0.5, 1.0 and 1.5 m s^?1) and air‐drying temperature (40, 50 and 60 °C). The bioactive compounds studied were L‐ascorbic acid, total phenolic, total flavonoids and antioxidant activity (expressed as IC₅₀) was determined using free radical DPPH^?. Both independent variables studied have shown to be statistically significant. The content of ascorbic acid was the highest at 60 °C and 1.0 m s^?1 (126.2 ± 0.004 mg 100 g^?1) while for the fresh residue 16.12 ± 0.003 mg 100 g^?1, whereas the total phenolic showed the highest content at 50 °C and 1.5 m s^?1 (46.2 ± 0.003 mg gallic acid.100 g^?1) while for the fresh residue 12.59 ± 0.001 mg gallic acid.100 g^?1. The drying conditions play an important role in determining the final quality of the product mainly in terms of antioxidant activity.     

Effect of temperature,pH and film thickness on nisin release from antimicrobial whey protein isolate edible films

BACKGROUND: An active packaging film based on whey protein isolate (WPI) was developed by incorporating nisin to promote microbial food safety. The effect of temperature and pH on the release of nisin from edible films of different thickness was investigated. The film mechanical properties and inhibitory effect were also evaluated. RESULTS: Nisin release was significantly favoured by low pH, with the highest release after 24 h (1325 IU), which was not significantly affected by temperature (5 or 10 °C). Thickness significantly affected film elongation, with thicker films showing the highest elongation (54.3 ± 2.7%). Water vapour permeability (0.15 ± 0.4 g mm m^?2 kPa^?1 h^?1) and elastic modulus were not significantly affected by thickness. The highest nisin effective diffusivity (5.88 × 10^?14 m² s^?1) was obtained using a solution at pH 4, 112 µm film thickness and a temperature of 5 °C. More than four log cycles of Brochotrix thermosphacta were reduced from the surface of a ham sample after 8 days of incubation at 4 °C by the active WPI film containing 473 IU cm^?2 nisin. CONCLUSION: Nisin diffusivity from WPI edible films was favoured at lower pH and film thickness. This active packaging film may be used to preserve the quality and safety of meat products. Copyright © 2009 Society of Chemical Industry     

Diffusion of Acetic and Propionic Acids from Chitosan-based Antimicrobial Packaging Films

The diffusion of acetic or propionic acids from thin (44 to 54 μm) chitosan‐based antimicrobial packaging films in which they were incorporated was measured after immersion of the films in water, and the effects of pH (5.7, 6.4, or 7.0) and temperature (4 °C, 10 °C, or 24 °C) on diffusion were investigated. The kinetics of acetic‐ and propionic‐acid release deviated from the Fickian model of diffusion. Diffusion was found to be unaffected by pH in the range of values tested, but a decrease in temperature from 24 °C to 4 °C resulted in a reduction of diffusion coefficients from 2.59 × 10^?12 m².s^?1 to 1.19 × 10^?12 m².s^?1 for acetic acid and from 1.87 × 10^?12 m².s^?1 to 0.91 × 10^?12 m².s^?1 for propionic acid. The effect of temperature on diffusion was well (r² > 0.9785) described by an Arrhenius‐type model with activation energies of 27.19 J.mole^?1 (acetic) and 24.27 J.mole^?1 (propionic). Incorporation of lauric acid or essential oils (cinnamaldehyde or eugenol) into the chitosan film at the time of preparation produced a subsequent reduction in the diffusion of acetic or propionic acid, and maximum effects were obtained with lauric acid and cinnamaldehyde incorporated to final concentrations of 1.0% and 0.5% (w/w), respectively.     

Studies on the palmitoyl-CoA hydrolase activity in carrot

Carrot homogenate contains a palmitoyl-CoA hydrolase. The enzyme was detected by spectrophotometric and radiochemical methods. The activation energy (Ea) for the reaction was determined to be 16700±2000 cal mol^?1 with a Q10 of 1.8. The rate of reaction reaches its maximum at 45°C and ceases completely at 55°C. The inactivation energy was found to be 67000±11000 cal mol^?1. A purification factor of 60 was obtained when polyvinylpyrolidone, polyethylene glycol, dithiothreitol and glycerol were used as stabilising agents, and the purification of palmitoyl-CoA hydrolase was carried out without delay. The method used successively, polyethylene glycol fractionation and DEAE-cellulose, hydroxylapatite and Ultrogel AcA 34 chromatography. Palmitoyl-CoA hydrolase has a molecular weight of 42000 daltons and a pI of 4.6. The role of this enzyme in the development of off-flavour in carrot has been discussed.     

Spray drying of low‐phenylalanine skim milk: optimisation of process conditions for improving solubility and particle size

The optimisation of the spray drying process for low‐phenylalanine skim milk as a dietary supplement for phenylketonurics was studied. The effects of basic parameters including the inlet air temperature (100, 150 and 200 °C), feed flow rate (5, 10 and 15 mL min^?1) and air flow rate (400, 600 and 800 L h^?1) on the solubility and particle size of the low‐phenylalanine skim milk powder were determined using response surface methodology. The optimum conditions have been obtained with inlet air temperature of 133 °C, feed flow rate of 5 mL min^?1, and air flow rate of 800 L h^?1. With the optimum parameters, the predicted values for the solubility and mean diameter were 95.33% and 5.34 μm, respectively, and experimentally were 94.36 ± 1.62% and 5.50 ± 0.44 μm, respectively. The experimental and predictive values were closely related showing predictive accuracy of the models.     

Kinetics of Ascorbic Acid Autoxidation as a Function of Dissolved Oxygen Concentration and Temperature

The kinetics of ascorbic acid autoxidation was studied at pH 6.1 (μ= 0.08) using a buffered model system. Oxygen replenishment in the solution was accomplished by shaking the reaction vessel in a shaker water bath or by bubbling oxygen-nitrogen gas mixtures through the solution. Using the former system, a second order rate constant of 58.19 ± 11.92 min^?1 M^?1 was calculated (45°C), Since the shaker bath did not assure oxygen replenishment and dissolved oxygen levels could not be varied, the latter system was developed. The second order rate constants in the gas mixture experiments ranged from 20.80 ± 2.28 min^?1 M^?1 (30°C) to 176 ± 6.93 min^?1 M^?1 (55°C). Activation energies measured under different conditions ranged from 9.47 to 16.43 kcal mole^?1.     

COD (GADUS MORHUA) TRYPSIN HEAT INACTIVATION: A REACTION KINETICS STUDY

The heat inactivation of cod (Gadus morhua) trypsin was examined at 40–55C by nonlinear regression (NLR) analysis according to 1st-order, n-th order, or consecutive reaction kinetics. At 40C Cod trypsin was inactivated by a 2nd-order reaction; n = 2 (±0.014) with a pseudo rate constant (k′) of 6.46 (±0.04) × 10^?4 (s^?1). The order of reaction decreased with increasing temperature; n = 1.54 (±0.003) at 45C, n = 0.8 (±0.005) at 50C or n = 0.64 (±0.014) at 55C. At 45–55C the consecutive model also indicated 1st-order inactivation kinetics. SDS-PAGE analysis showed that with progressive heating the concentration of cod trypsin decreased and there was an appearance of lower molecular weight polypeptides. The results are consistent with a heat inactivation process involving trypsin autolysis. A mechanism for cod trypsin heat inactivation is proposed which accounts for the observed 1st-order or 2nd-order reaction kinetics as limiting cases.     

Thermal Properties of Sweet Potato with its Moisture Content and Temperature

Thermal properties of sweet potato were experimentally determined and modeled as a function of temperature and moisture content. The purpose is to develop empirical correlations that could predict thermal properties during sweet potato processing. Thermal conductivity from the study was 0.49 ± 0.038 Wm^?1K^?1 (mean ± s.d.), thermal diffusivity was 1.2?×?10^?7 ± 9.05?×?10^?9 m²s^?1, specific heat was 3660 ± 477.4 Jkg^?1K^?1, and density was 1212 ± 73.5 kgm^?3. All properties were determined within temperature range of 20 to 60°C and moisture content range of 0.45 to 0.75 w.b. Prediction models for the thermal properties of sweet potato were developed as a function of product temperature and moisture content with experimental data from this study. Mechanistic models were also developed for thermophysical properties of sweet potato using major food components of the product. Developed models were all presented and compared.     

Effects of pressurized thermal processing on native proteins of raw skim milk and its concentrate

Heating, pressurization, and shearing can modify native milk proteins. The effects of pressurized heating (0.5 vs. 10 MPa at 75 or 95°C) with shearing (1,000 s^?1) on proteins of raw bovine skim milk (SM, ～9% total solids) and concentrated raw skim milk (CSM, ～22% total solids) was investigated. The effects of evaporative concentration at 55°C and pressurized shearing (10 MPa, 1,000 s^?1) at 20°C were also examined. Evaporative concentration of SM resulted in destabilization of casein micelles and dissociation of α_S1- and β-casein, rendering CSM prone to further reactions. Treatment at 10 MPa and 1,000 s^?1 at 20°C caused substantial dissociation of α_S1- and β-casein in SM and CSM, with some dissociated caseins forming shear-induced soluble aggregates in CSM. The pressure applied at 10 MPa induced compression of the micelles and their dissociation in SM and CSM at 75 or 95°C, resulting in reduction of the micelle size. However, 10 MPa did not alter the mineral balance or whey proteins denaturation largely, except by reduction of some β-sheets and α-helices, due to heat-induced conformational changes at 75 and 95°C.     

Wood–water relations of chestnut wood used for structural purposes

Hygroscopic properties and water vapour permeability of chestnut (Castanea sativa Mill.) wood were studied using saturated salt solutions, and the results were analyzed using the Hailwood–Horrobin model. At 20 °C/65 % the equilibrium moisture content (MC _eq ) and density were 11.5 ± 0.1 % and 576.6 ± 10.2 kg m^?3, respectively, and the fiber saturation point was 20.83 %. The average water vapour permeability was 0.320 kg m^?1 s^?1 Pa^?110⁸, lower than that of Radiata pine (0.726 kg m^?1 s^?1 Pa^?110⁸). Furthermore, there was no difference in permeability between tangential and radial cuts. This low permeability is explained by the scant development of the multilayer of the Hailwood–Horrobin model. This is attributed to the wood extractives, which reduce the void space and hindered condensation. Chestnut wood has different vapour sorption and vapour permeability than conifers normally used in construction.     

Optimization of Covalent Immobilization of Extracellular Ice Nucleators from Erwinia herbicola on Magnetic Fe3O4/Chitosan Nanoparticles for Potential Application in Freeze Concentration

A magnetically separable extracellular ice nucleators (ECINs) immobilized system was constructed, ECINs from Erwinia herbicola were covalently immobilized on magnetic Fe₃O₄/chitosan nanoparticles by coupling via glutaraldehyde (GA) or epichlorohydrin (ECH). The immobilization process parameters were optimized, and under optimized conditions, ice nucleation activity (INA) of GA and ECH immobilized ECINs reached at 1.56?×?10⁶?±?1.54?×?10⁵ Units/mg and 1.62?×?10⁶?±?1.91?×?10⁵ Units/mg, respectively. The stability, reusability and cytotoxicity of GA and ECH immobilized ECINs were characterized and compared; both GA and ECH immobilized ECINs demonstrated good reusability performance after 15 freeze–thaw cycles and low cytotoxicity, while GA immobilized ECINs were recovered more easily and more stable at different pH compared to ECH immobilized ECINs. Application of the immobilized ECINs in freeze concentration was investigated, and an increase of ice nucleation temperature for water, seawater and apple juice (6.83?±?0.18 °C, 8.08?±?0.50 °C and 9.38?±?1.12 °C) was achieved by using GA immobilized ECINs. The results collected so far show that there are extensively promising applications for GA immobilized ECINs in freeze concentration industry fields.     

Sorption of ethyl acetate and d‐limonene in poly(lactide) polymers

Poly(lactide) (PLA) polymers have garnered increased attention in the last few years as food packaging materials because they are environmentally friendly polymers. As the production of PLA increases and price per pound drops, PLA is becoming a growing alternative as a green food packaging material. In this research, the organic vapor barrier properties of commercially available PLA polymers were studied. Gravimetric sorption tests in PLA films were carried out, and the diffusion (D), solubility (S) and permeability (P) coefficients for ethyl acetate and d‐limonene in PLA were determined. For ethyl acetate, values of P = 1.22 × 10^?17 kg m m^?2 s^?1 Pa^?1, D = 2.63 × 10^?15 m² s^?1, and S = 4.62 × 10^?3 kg m^?3 Pa^?1) at 45 °C and a partial pressure of 12 654 Pa were obtained. For d‐limonene, no trace was detected after 21 days of testing at 45 °C and 258 Pa, which indicates a permeability coefficient lower than 9.96 × 10^?21 kg m m^?2 s^?1 Pa^?1. Poly(lactide) polymers demonstrated good aroma barrier to ethyl acetate and d‐limonene, and will most likely be good aroma barriers. PLA is not likely to promote flavor loss by either permeation or scalping. Copyright © 2005 Society of Chemical Industry     

Degradation kinetics of β-carotene in carrot slices during convective drying

The β-carotene degradation was investigated in carrot (Daucus carota L. cv Nantes) slices during convective drying at three temperatures (45, 55, and 65°C) at an airflow rate of 0.2 m s^–1. Degradation kinetics of β-carotene in carrot slices during convective drying followed a first-order reaction. Drying temperature showed a significant effect on the degradation of β-carotene in carrot slices. The range of the reaction rate constants for β-carotene loses were 0.23 ± 0.08 –0.48 ± 0.04 h^–1. The activation energy of β-carotene degradation is found 33.33 ± 0.05 kJ mol^–1. Half-life time was calculated as 3.02 ± 0.04 h at 45°C, which dropped to 1.43 ± 0.03 h at 65°C.     

KINETICS OF THE INTERACTION OF PANCREATIC α-AMYLASE WITH A KIDNEY BEAN (PHASEOLUS VULGARIS) - AMYLASE INHIBITOR

An amylase inhibitor isolated from black beans (Phaseolus vulgaris) can completely inhibit porcine pancreatic α-amylase forming a 1:1 stoichiometric complex. The kinetic pattern of complex formation is pH dependent. At pH 5.5 it follows a first order reaction with rate constant of 0.029 min^?1 and 0.017 min^?1 at 37°C and equimolar inhibitor and enzyme concentration, respectively, of 10^?8 M and 10^?9 M. At pH 6.9 it is a second order reaction, with a rate constant of 0.25 × 10⁶ M^?1 min^?1 at 37°C, with 4 × 10^?8 M concentrations of enzyme and inhibitor. The dissociation constants of the enzymeinhibitor complex are 1.7 × 10^?10 M at pH 5.5 and 4.4 × 10^?9 M at pH 6.9, at 37°C. The kinetic data obtained at pH 5.5 suggested the formation of an initial reversible complex followed by a conformational change step. The complex can be dissociated either in acid pH (4.3) or at pH values higher than 6, 5 with partial recovery of the amylase activity.     

Novel Procedure for Lager Beer Clarification and Stabilization Using Sequential Enzymatic,Centrifugal, Regenerable PVPP and Crossflow Microfiltration Processing

In this work, the crossflow microfiltration (CFMF) performance of different lots of lager beer, produced in a pilot scale at the Italian Brewing Research Centre (CERB, Perugia, Italy), was assessed in a bench-top plant, equipped with a 0.8-μm ceramic tubular membrane module, under constant crossflow velocity of 6 m s^?1, transmembrane pressure difference of 3.74 bar, temperature of ~10 °C, and periodic CO₂ backflushing. By feeding different beer samples (i.e., as such, precentrifuged (C), or pretreated with a commercial enzyme preparation to degrade the original arabinoxylans and β-glucans and then centrifuged (EC) to minimize the fouling contribution of yeast cells, aggregates, and polysaccharides), it was possible to increase the average permeation flux (expressed as mean value?±?standard deviation) from 112?±?13 to 199?±?17 or 330?±?22 L m^?2 h^?1, respectively. Only when using the EC-pretreated beer specimens, the permeate turbidity at 20 °C approached the limiting one (<0.6 EBC unit) recommended by the European Brewery Convention standards. As expected, the permeate chill haze at 0 °C was generally higher than the above haze target. By submitting EC-pretreated beer seeded with 0.5 g L^?1 of regenerable polyvinylpolypyrrolidone (PVPP) to CFMF, it was possible to reduce the initial total polyphenol content by 30 % and permeate chill haze to 0.60?±?0.01 EBC unit, but the average permeation flux fell to 84?±?4 L m^?2 h^?1. By performing sequentially EC pretreatments, PVPP stabilization, cartridge filtration, and CFMF, it was possible not only to re-enhance the average permeation flux at about 230 L m^?2 h^?1 near to those achievable with DE filters, but also to obtain a chill haze-free permeate ready for aseptic packaging.     

Characterization of hot air drying and microwave vacuum drying of fingerroot (Boesenbergia pandurata)

Fingerroot (Boesenbergia pandurata) was subjected to hot air drying and microwave vacuum drying. Effective moisture diffusion coefficient during the hot air drying at 60 and 70 °C were 0.2073 × 10^?10 and 0.4106 × 10^?10 m² s^?1 respectively. By using the microwave vacuum drying (13.3 kPa) at the power of 2880 and 3360 W, the effective moisture diffusion coefficient were increased to 5.7910 × 10^?10 and 6.8767 × 10^?10 m² s^?1 respectively. Based on Lewis model, drying rate constants were 0.0002, 0.0004, 0.0061 and 0.0072 s^?1 for the hot air drying at 60 and 70 °C and the microwave vacuum drying at 2880 and 3360 W respectively. Compared with the hot air drying, the microwave vacuum drying decreased drying time by 90%. Rehydration ability of the microwave vacuum dried samples was also significantly improved (P ≤ 0.05), because of porous structure. In addition, the rehydrating water of the microwave vacuum dried samples contained higher b*‐value (yellowness) than that of the hot‐air‐dried samples (P ≤ 0.05).     

Determination of Volumetric Coefficients of Thermal Expansion in Alcoholic Beverages and Aqueous Ethanol–Sucrose Mixtures by Differential Volume Measurements

The volumetric coefficient of thermal expansion (CTE) of diverse alcoholic beverages and aqueous ethanol?Csucrose mixtures was calculated by a simple experiment in the temperature range of 5?C30°C at atmospheric pressure. The temperature and volume corresponding changes were measured using a basic device as a dilatometer type. Alcohol degree, titratable acidity, volumetric mass, total dry extract, reducing sugars, total polyphenol index, and conductivity in different wine types and other alcoholic beverages were studied to correlate with CTE values. Multivariate techniques were used to study the data, essentially to reveal any widespread patterns in the alcoholic beverages. Additionally, the error of the CTE measurements was also estimated. The CTE obtained results for alcoholic beverages ranged from 1.9?±?0.3 (×10^?4°C^?1) for white wines to 11.7?±?0.4 (×10^?4°C^?1) for rectified alcohol samples. In the sucrose?Cethanol?Cwater mixtures the experimental results of CTE ranged from 2.0 to 6.5?±?0.01 (×10^?4°C^?1). Based on the results obtained, the CTE values depend mainly of alcohol degree and volumetric mass of the samples. The knowledge of volumetric coefficient of thermal expansion will be useful to estimate thermal induced volume changes and to check the accurate quantities in stored bulk beverages or during its ageing.