Pseudo-zero Order Kinetics Research Articles

Evaluating β-cryptoxanthin antioxidant properties against ROS-induced macromolecular damages and determining its photo-stability and in-vitro SPF.

Natural antioxidants have become vital to minimize macromolecular damage caused by Reactive Oxygen Species (ROS). This study investigated the antioxidant property of β-cryptoxanthin (β-CRX) extracted fromKocuria marinaDAGII and its protective effect against macromolecular damages by generating ROS via two models: UV radiation and the Fenton reaction. β-cryptoxanthin exhibited the highest scavenging activity towards hydrogen peroxide radicals with an IC50 value of 38.30 ± 1.13μg/ml, favoring the hydrogen atom transfer mechanism. The total antioxidant capacity value of 872.0101 ± 1.84μg BHT/mg β-CRX indicated the cumulative ROS scavenging ability of β-cryptoxanthin. β-cryptoxanthin could protect against ROS-induced lipid peroxidation, protein oxidation, and DNA damage. The highest lipid peroxidation and protein oxidation inhibition values of β-cryptoxanthin against ROS were 99.371 ± 0.51% and 78.19 ± 0.15%, respectively. β-cryptoxanthin also showed a protective effect in maintaining DNA intactness against ROS-mediated DNA damage.Allium cepatest showed the non-genotoxic nature of β-cryptoxanthin and its protective effect against ROS genotoxic effects. A photo-stability study of β-cryptoxanthin toward UVA and UVB radiation showed a rapid bleaching result of UVB obeying pseudo-zero order kinetics with an average R2 value of 0.9897 and a higher k value (-6.3 × 10-11 ± 0.2M/s) than UVA (k value -3.1 × 10-11 ± 0.17M/s), signifying that UVB is more potent toward photo-degradation. The good SPF value of 23.1737 ± 0.15 showed the UV protection capability of β-cryptoxanthin. Thus, the present study suggests that β-cryptoxanthin could be a valuable antioxidant to protect against ROS-induced various macromolecular damages and act as a good UV protectant.

Epoxidation of melon seed (Citrullus colocynthis L) oil: A kinetic and thermodynamic approach for industrial applications

Unsaturated melon seed oil had its epoxidation process studied at varied temperatures (30OC -70OC) within a three hours reaction time, for possible oxirane formation because of its industrial significance. Oil was extracted from melon seeds and characterized for its physicochemical properties using standard methods. The specific gravity (30OC), iodine value, acid value, saponification value, peroxide value and percentage oil content were found as 0.931, 118.69 gI2/100g, 5.08 mg KOH/g, 165.7 mg KOH/g, 4.75 meq/kg and 60% respectively. Physicochemical characteristic of the oil reveals it is semi-drying oil which is rich in high molecular weight fatty acids, with good stability against rancidity. The epoxidation process which was monitored by its oxirane content is seen to proceed faster at the highest studied temperature of 70OC, giving the highest oxirane content of 5.87%. Optimization of the epoxidation process showed that optimum epoxidation of melon seed oil can be achieved at 70OC within one hour; as compared to other temperatures studied. Process kinetics evaluated in terms of its oxirane yield showed that the epoxidation process followed pseudo-zero order kinetics with respect to oxirane formation. Their rate constants were found to be 0.032 hr-1, 0.041 hr-1, 0.059 hr-1 and 0.24 hr-1 for the epoxidation process at 30OC, 50OC, 60OC and 70OC respectively; which shows that the epoxidation rate increases with increasing temperature. Thermodynamic parameters such as activation energy (Ea), activation enthalpy (∆H≠), activation entropy (∆S≠) and Gibb’s free energy (ΔG≠) were determined to be 133.11 kJmol-1, 18.22 kJmol-1, -0.21 kJmol-1 K-1 and 87.95 kJmol-1 respectively. The observed thermodynamic properties indicated strong temperature dependence of the epoxidation reaction rate, endothermicity and non-spontaneity of the process. The findings of this study will guide in maximizing oxirane yield and save cost significantly in the production of epoxidized melon seed oil employed for large scale industrial applications.

A Desilylative Approach to Alkyl Substituted C(1)-Ammonium Enolates: Application in Enantioselective [2+2] Cycloadditions.

The catalytic generation of C(1)‐ammonium enolates from the corresponding α‐silyl‐α‐alkyl substituted carboxylic acids using the isothiourea HyperBTM is reported. This desilylative approach grants access to α‐unsubstituted and α‐alkyl substituted C(1)‐ammonium enolates, which are typically difficult to access through traditional methods reliant upon deprotonation. The scope and limitations of this process is established in enantioselective [2+2]‐cycloaddition processes with perfluoroalkylketones (31 examples, up to 96 % yield and >99 : 1 er), as well as selective [2+2]‐cycloaddition with trifluoromethyl enones (4 examples, up to 75 % yield and >99 : 1 er). Preliminary mechanistic studies indicate this process proceeds through an initial kinetic resolution of an in situ prepared (±)‐α‐silyl‐α‐alkyl substituted anhydride, while the reaction process exhibits overall pseudo zero‐order kinetics.

Evaluation of Kinetic Pseudo-Order in the Photocatalytic Degradation of Ofloxacin

Ofloxacin is a highly efficient and widely used antibiotic drug. It is classified as a refractory pollutant due to its poor biodegradability. Consequently, it is commonly found in water sources, requiring efficient methods for its removal. Advanced oxidation processes (AOPs) offer efficient alternatives since those yield complete degradation not achieved in adsorption or membrane processes. Previous studies suggest ofloxacin degradation follows a pseudo-first or -second order processes, whereas for full removal of refractory pollutants—lower pseudo-orders are required. Monitoring the actual “pseudo-order” degradation kinetics of ofloxacin is needed to evaluate any proposed AOP process. This study presents a simple procedure to evaluate pseudo-orders of AOPs. Photolysis of 20 μM ofloxacin solutions follow pseudo-zero order kinetics, with half-life times (t1/2) of approx. 60 min. TiO2 heterogenous catalysts have been shown to have no influence at low concentrations (0.2 mg L−1), but a significant reduction of half-life time (t1/2 = 20 min) and increase in pseudo-order (0.8) is measured at 2.0 mg L−1. Similar results are obtained with homogenous catalysis by 2.0 mg L−1 H2O2. The combination of H2O2 and TiO2 catalysts shows additional reduction in half-time life with increase in the pseudo-order to 1.2. The conclusions are (1) heterogenous and homogenous photocatalysis can effectively degrade ofloxacin, (2) combined photocatalysis yields higher pseudo-order, being less prone to achieve full removal, and (3) analysis of specific pseudo-orders in AOPs of refractory pollutants helps to further elucidate the efficiency of the processes.

Degradation of bioplastics in organic waste by mesophilic anaerobic digestion, composting and soil incubation

The aim of the study was to assess the effects of high concentrations (10 % w/w, data projected for 2030) of commercial bioplastics, i.e. starch based shopping bags (SBSB) and polylactic acid (PLA) tableware, in the organic fraction of municipal solid wastes (MSW) on compost quality obtained by pilot-scale dry mesophilic anaerobic digestion and subsequent composting of the digestate.After the biological processes, 48.1 % total solids (TS) of SBSB and 15 % TS of PLA degraded, resulting in a high bioplastics content (about 18 % TS) in compost. Subsequent compost incubation in soils indicated that bioplastics degraded by pseudo-zero order kinetics (0.014 and 0.010 mg C cm−2 d-1 for SBSB and PLA, respectively), i.e. complete degradation was expected in 1.6 years (SBSB) and 7.2 years (PLA), confirming the intrinsic biodegradability of bioplastics. Nevertheless, enhancing the rate and amount of bioplastics degradation during waste management represents a goal to decrease the amount of bioplastics reaching the environment.

Photocatalytic degradation of imidacloprid in the flat-plate photoreactor under UVA and simulated solar irradiance conditions—The influence of operating conditions, kinetics and degradation pathway

This work reports the effectiveness of TiO2 photocatalysts modified by defect engineering methods. The prepared photocatalysts were characterized by X-ray diffraction (XRD), UV–Vis diffuse reflectance spectroscopy (DRS), photoluminescence (PL) measurements and electron spin resonance (ESR) technique. The immobilized photocatalyst layer was prepared using an abrasive material as a support and a mineral binder. To the best of our knowledge, this is the first time that such type of the immobilized photocatalytic layer has been prepared and tested. A home-made flat-plate photoreactor (FPP) with artificial light sources was used for the degradation of an aqueous solution of imidacloprid using an immobilized TiO2. The effects of different operating variables such as irradiation source, recirculation flow rate, irradiated surface area and photoreactor volume on the photocatalytic performances were investigated. The hydrodynamic behavior of the flat-plate photoreactor (FPP) was studied utilizing a residence time distribution (RTD) technique using the axial dispersion model. Based on kinetic measurements it was found that the photocatalytic degradation of imidacloprid under the conditions used in this study can be described by a complex kinetic model that follows pseudo-zero order kinetics at the beginning of the degradation, and with the progress of the reaction at higher irradiation times changes to the pseudo-first order. Liquid chromatography - quadrupole time‐of‐flight mass spectrometry (LC‐QTOF‐MS) was used to identify imidacloprid degradation by-products as a function of irradiation time. Theoretical modeling of the geometry and electronic structure of imidacloprid in aqueous solution was performed using density functional theory (DFT) calculation. Based on the results of theoretical simulations and experimental measurements, the possible pathway for photodegradation of imidacloprid in aqueous phase after irradiation with UVA was proposed and discussed.

Electrochemical ammonia removal and disinfection of aquaculture wastewater using batch and flow reactors incorporating PtRu/graphite anode and graphite cathode

Ammonia removal and disinfection are two major problems in aquaculture systems, which require clean and reliable water to support long-term growth and health of target animals. In this study, we report electrochemical ammonia removal and disinfection of wastewater from an aquaculture farm (Mari’s Gardens) in Hawaii. First, we attempted to reproduce the work of Zollig and co-authors, who reported that direct ammonia oxidation can occur between 1 V and 1.6 V vs SHE on a graphite electrode in a solution (pH = 9.0) containing 1 M NaClO4, 0.25 M NH4ClO4, and 0.085 M NaCl. Our results, however, show that direct ammonia oxidation is unlikely to occur, at least at significant rates, on a graphite electrode in aqueous solutions (pH = 9.0) containing 0.7 M Na2SO4, 0.1 M (NH4)2SO4, and 0.02 M NaCl. We tentatively attribute this discrepancy to the different physico-chemical characteristics of graphite electrodes made by different manufacturers. Second, PtRu/graphite electrodes were prepared using a pulsed electrodeposition method, and electrode activity towards ammonia removal and disinfection was examined in both synthetic and real aquaculture wastewater using batch and flow reactors. The PtRu catalyst was partially oxidized at the beginning of electrolysis, and a significant increase in the electrode activity towards indirect ammonia oxidation was observed. Ammonia removal was slow when NaCl concentration was 0.66 mM, but the addition of NaCl (up to 20 mM) led to a drastic increase in the ammonia removal rate, indicating that ammonia removal proceeds via indirect oxidation. The ammonia removal rate depends primarily on NaCl concentration and current density and is independent of the initial ammonia concentration and solution pH. The ammonia removal rates can be modeled by pseudo zero-order kinetics, and a linear correlation can be drawn between the ammonia removal rate (k, mg L−1 min−1) and the product of NaCl concentration ([Cl-], mM) and current density (j, mA/cm2): k = 0.0047 [Cl-] j (R2 = 0.99). Free chlorine (Cl2, HOCl, and OCl-) was not detected in the solution until the complete removal of ammonia. Combined chlorine (NH2Cl, NHCl2, and NCl3) was measured at concentrations of 2–15 mg/L (as Cl2) during the ammonia removal process but was eliminated as soon as ammonia was depleted and an excess of free chlorine was available. Our detailed findings on the formation of both free chlorine and combined chlorine are significant to the mechanistic study of indirect ammonia oxidation. Ammonia removal experiments in synthetic and real aquaculture wastewater showed similar results. However, ammonia removal in the flow reactor took about three times longer than that in the batch reactor under similar conditions, likely due to hydrodynamic mixing differences. In addition, it was found that E. coli bacteria can be completely inactivated (5-log reduction) within a short time (e.g., 5 min).

Real time monitoring of in situ generated hydrogen peroxide in electrochemical advanced oxidation reactors using an integrated Pt microelectrode

This work propose the fabrication and characterization of a Pt microelectrode integrated with a silver quasi-reference counter electrode (Pt/AgQRCE) for real time amperometric measurements of hydrogen peroxide electrochemically generated by water oxidation on Nb-supported boron doped diamond (Ni/BDD) anode. The developed electroanalytical method requires a very small sample volume and has higher sensitivity when compared to the conventional spectrophotometric analysis using ammonium metavanadate. The experiments were performed with Nb/BDD anode applying current densities of 30, 60, 90 and 120 mA cm−2 in 0.10 mol L−1 HClO4 supporting electrolyte showed that H2O2 production increase in the first 90 min of electrolysis and then reaches a plateau in both off-line and real time measurements. For the first 90 min, the electrogeneration of H2O2 exhibited a pseudo zero-order kinetics. The results obtained by the electrochemical amperometric analysis were compared to a spectrophotometric methodology reported on the literature and, at 95% confidence level the two methods do not demonstrated significant difference.

Effect of Ag Co-catalyst on TiO2–Cu2O nanocomposites structure and apparent visible photocatalytic activity

Although Cu2O is a commonly used narrow band gap semiconductor to fabricate visible response photocatalysts, up to date there are only a few reports on Ag co-catalysed TiO2–Cu2O nanocomposites. Herein we report a facile wet chemical synthesis approach to prepare TiO2–Ag–Cu2O ternary hybrid nanomaterials. Uniquely, both the effect of Ag content and the synthesis sequence of Ag deposition step was investigated on the visible decoloration rate. The crystal structure, morphology, optical and dark adsorption properties of the nanostructures were characterized by XRD, SEM, TEM and diffuse reflectance, respectively. Due to the mixed indirect and direct nature of the nanocomposites, the band gap estimation was performed by using both Tauc plot and differential reflectance model. The dark adsorption properties of catalysts could be typically well-approximated by pseudo-second order kinetics, while TiO2–Ag(5%)-Cu2O catalyst cannot be described by standard models due to a delayed adsorption behaviour observed in the first 50 min. The apparent visible activities followed pseudo-zero order kinetics. It was found that TiO2–Ag(3%)-Cu2O catalyst exhibited the highest rate constant which was ca. two times as high as that of the binary TiO2–Cu2O catalyst. The synthesis sequence of the Ag deposition step significantly altered the material properties which resulted in different dark adsorption and apparent visible activities.

Study of the atenolol degradation using a Nb/BDD electrode in a filter-press reactor

The present paper deals with the atenolol (ATL) degradation by advanced anodic oxidation using a boron-doped diamond anode supported on niobium (Nb/BDD). Cyclic voltammetry performed on this electrode revealed that it presents a high quality (diamond-sp3/sp2-carbon ratio), high potential for OER and that ATL can be oxidized directly and/or indirectly by the electrogenerated oxidants, such as hydroxyl radicals, persulfate ions and sulfate radicals.Electrolysis experiments demonstrated that ATL degradation and mineralization follow a mixed (first and zero) order kinetics depending on the applied current density. At high applied current densities, the amount of OH radicals is very high and the overall reaction is limited by the transport of ATL (pseudo first-order kinetics) whereas for low applied current densities, the rate of OH radicals generation at the anode is slower than the rate of arrival of ATL molecules (pseudo-zero order kinetics). Estimated values of kzero and kfirst based on the assumption of pseudo-zero or pseudo-first order kinetics were carried oud as a function of the supporting electrolyte concentration, indicating that both parameters increased with its concentration due the higher production of sulfate reactive species that play an important role in degradation.Finally, MCE increased with the decrease of current density, due to the lower amount of OH present in solution, since this species could be rapidly wasted in parasitic reactions; and the increase of sulfate concentration due to the more efficient production of persulfate.

ZnO/CuO nanocomposites from recycled printed circuit board: preparation and photocatalytic properties.

Cost-effective recycling of e-waste (from computer printed circuit boards, PCB's) for the synthesis of metal oxide nanocomposites is demonstrated. Metals in electronic components of waste memory slots were leached out using nitric acid (HNO3). Compositional analyses of the filtrate obtained after leaching were 66wt.% Cu, 27.7wt.% Zn, and 6.2wt.% Ni. The leached out metal salt solutions were subjected to alkaline hydrothermal treatment to synthesize nanocomposites. Two nanoparticle samples were prepared, one without any stabilizing agent and another sample with PVP as a stabilizing agent. XRD, HR-XRD, HR-TEM, UV-DRS, UV-visible spectroscopy was used to characterize the as-prepared metal oxide nanoparticles. The analysis showed the formation of ZnO/CuO nanocomposites only. No nickel oxide component was precipitated under the studied hydrothermal experimental conditions. Most of the ZnO/CuO nanocomposite particles obtained by this route consisted of fine ZnO nanostructures precipitated on CuO cores. The ZnO and CuO components exhibit both direct and indirect band gaps in the visible range. The nanocomposites demonstrate good visible light photo-Fenton methyl orange (MO) degradation by pseudo-zero order kinetics.

Non-isothermal decomposition kinetics of conductive polyaniline and its derivatives

Abstract The non-isothermal decomposition kinetics of conductive polyaniline (PANI) and its derivatives, poly(o-methoxyaniline) (POMA) and poly(o-ethoxyaniline) (POEA), was investigated by thermogravimetric analysis (TGA), under inert and oxidative atmospheres, using Flynn-Wall-Ozawa’s approach to assess the kinetic parameters of the decomposition process. The order of reaction was found to be dependent on the degree of conversion indicating that both the early and the later stages of polymer degradation were next the zero or pseudo zero order kinetics, whereas the intermediate stages follow a first order kinetics. The activation energy was found to be dependent on both the degree of conversion and PANI derivative. Activation energy values vary from 125 to 250 kJ/mol, to decompositions carried out under nitrogen, and 75 to 120 kJ/mol to oxidative atmosphere. Parent PANI presented the best thermal stability and suggesting that thermal stability is also influenced by derivatization and type of atmosphere used.

Effect of hydrolytic degradation on the mechanical property of a thermoplastic polyether ester elastomer

Polymers with a finite lifetime are of great interest for oil and gas industry. Thermoplastic elastomers (TPEs) combine the strength of thermoplastics with the flexibility of elastomers, a characteristic also potentially useful in oil and gas applications. We studied the hydrolytic degradation of a TPE of interest at elevated temperatures from both a mechanical and chemical perspective, and have demonstrated that the chemical degradation rates, the change in crystallinity and the storage modulus all follow the pseudo zero order kinetics with respect to varying time at three temperatures. Applying Arrhenius' empirical relationship to the determined rates gives rise to a temperature-dependent model that predicts the degradation behavior of the TPE outside of the experimental temperature range. Our results indicate that hydrolytic degradation leads to an increase of crystallinity (chemicrystallization) and a decrease of tensile strength and strain, and that the increase of crystallinity strongly correlates to the increase of the storage modulus. The polymer eventually deteriorates due to brittleness.

Simulation of phase I metabolism reactions of clozapine by HLM and photocatalytic methods with the use of UHPLC-ESI-MS/MS.

In this study the comparison of human liver microsomes in in vitro incubation as well as ZnO- and TiO2 -assisted photocatalytic degradation of clozapine as a mimicking method of phase I metabolism transformation was performed. Based on reversed-phase UHPLC separation and high-resolution MS/MS data, eight transformation products were identified and seven of them were found to be hepatic metabolites of the parent compound. The multivariate chemometric comparison of the obtained results shows ZnO-assisted photocatalysis to be a more suitable approach to phase I metabolism simulation. The photocatalytic experiments demonstrated that the disappearance of clozapine followed pseudo-zero order kinetics.

Stability effects of methyl β-cyclodextrin on Olea europaea leaf extracts in a natural deep eutectic solvent

Polyphenol-containing extracts from olive (Olea europaea) leaves (OLL) were obtained using a glycerol-based deep eutectic solvent (DES) and a combination of DES with methyl β-cyclodextrin (m-β-CD). The extracts were stored at various temperatures for a period of 20 days and the reducing power (PR) was monitored to trace changes in the antioxidant potency of the extracts. Over the examination period and at every temperature tested, PR displayed a constant decline, which followed pseudo zero-order kinetics. The determination of the decay constants indicated that the presence of m-β-CD acted protectively, slowing down the progression of the PR decline. Examination of the polyphenolic profiles using liquid chromatography–diode array–mass spectrometry showed that after storage for 20 days at 50 °C, some major polyphenols occurring in OLL suffered extended degradation. The formation of a yellow pigment in the extracts stored in DES but not in aqueous ethanol suggested that polyphenol oxidation did occur during storage. It was concluded that the oxidation of some OLL components was rather responsible for the PR decline observed.

Chemical Kinetics of Alkaline Pretreatment of Napier Grass (Pennisetum purpureum) Prior Enzymatic Hydrolysis

Background:Napier grass is a naturally abundant waste material that can be cultivated over a vast area of land which makes it a viable source for sugar and bioethanol production.Introduction:The presence of lignin in the biomass makes cellulose inaccessible for conversion to useful products, however, in order to provide for efficient utilization of the waste material, reagent and energy, a study on the kinetics of lignin removal from Napier grass was carried out in this work using 1 and 3 w/w % NaOH at temperatures between 80 and 120°C.Materials & Methods:Based on the investigation, there was increased lignin removal for increased NaOH concentration. Kinetic parameters were also determined and it was observed that, the reaction of lignin in Napier grass with NaOH obeys a pseudo-zero or pseudo-fractional order kinetics. Furthermore, the orders of the reaction for the pretreatment conditions of 3 w/w% NaOH at 100°C and those of 3 and 1 w/w NaOH at 120°C gave close reaction orders of 0.2, 0.22 and 0.24 respectively after 110 minutes, which implies that, for the three cases, the residual lignin in the extract was almost the same at the pretreatment conditions while slight differences are evident in their pseudo rate constants. Also, it was observed that, the activation energy of the reaction reduced significantly as the concentration of NaOH increased from 1w/w - 3 w/w%.Conclusion:Based on the AIL and the total lignin (i.e.AIL + ASL) in the Napier grass, the recorded delignification efficiencies at the optimum pretreatment time of 17.5 h are 90 and 76% respectively. In addition, the adopted Differential Technique (DT) combined with the Ostwald Method of Isolation (OMI) can be accurately used to study the kinetics of lignin removal from Napier grass.

SrCo1\u2212xTixO3\u2212\u03b4 perovskites as excellent catalysts for fast degradation of water contaminants in neutral and alkaline solutions

Perovskite-like oxides SrCo1−xTixO3−δ (SCTx, x = 0.1, 0.2, 0.4, 0.6) were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for phenol degradation under a wide pH range, exhibiting more rapid phenol oxidation than Co3O4 and TiO2. The SCT0.4/PMS system produced a high activity at increased initial pH, achieving optimized performance at pH ≥ 7 in terms of total organic carbon removal, the minimum Co leaching and good catalytic stability. Kinetic studies showed that the phenol oxidation kinetics on SCT0.4/PMS system followed the pseudo-zero order kinetics and the rate on SCT0.4/PMS system decreased with increasing initial phenol concentration, decreased PMS amount, catalyst loading and solution temperature. Quenching tests using ethanol and tert-butyl alcohol demonstrated sulfate and hydroxyl radicals for phenol oxidation. This investigation suggested promising heterogeneous catalysts for organic oxidation with PMS, showing a breakthrough in the barriers of metal leaching, acidic pH, and low efficiency of heterogeneous catalysis.

A kinetic approach to predict the potential effect of malaxation time-temperature conditions on extra virgin olive oil extraction yield

An original kinetic study of both oil coalescence phenomena and potential extra virgin olive oil extraction yield (i.e. apparent Extractability Index) was carried out at different malaxation time-temperature conditions using Abencor lab equipment to process olives (Frantoio cv) of a known degree of ripeness.The apparent Extractability Index was modelled at every malaxation temperature by pseudo first-order kinetics, where the yield rate constant was temperature dependent following the Arrhenius equation (k0 = 7.50 107 min−1; Ea = 54512 J/mol). Oil droplet coalescence, which was expressed as a relative variation in the percentage of oil droplets with a diameter of >30 μm, proved to be an time-dependent phenomenon only; the pseudo zero-order kinetics modelling was statistically significant, where the coalescence rate constant was equal to 0.033 min−1. The above kinetics were applied in order to propose a synoptic chart to predict the potential effect of malaxation in isothermal conditions on EVOO extraction yield.

Comparative thermal impact of two UHT technologies, continuous ohmic heating and direct steam injection, on the nutritional properties of liquid infant formula

A continuous pilot plant for liquid sterilization was used to compare ohmic heating and steam injection on liquid infant formula under the same conditions of pre-heating and holding. Samples were collected at different holding times and temperatures and analyzed for reactions of thermal degradation. Two substrates were measured: soluble proteins and vitamin C and different intermediate or advanced products of Maillard reaction were monitored: furosine, carboxymethyllysine (CML), FAST index (Fluorescence of Advanced Maillard products and Soluble Tryptophan) and color (ΔL*, Δa* and Δb*). Pseudo-zero order kinetics was established for the Maillard products or global markers and Arrhenius parameters could be calculated. Equivalent markers contents were obtained after ohmic heating and steam injection showing equivalent quality of the infant formula for both sterilization technologies.

Simulating shelf life determination by two simultaneous criteria

The shelf life of food and pharmaceutical products is frequently determined by a marker's concentration or quality index falling below or surpassing an assigned threshold level. Naturally, different chosen markers would indicate different shelf life for the same storage temperature history. We demonstrate that if there are two markers, such as two labile vitamins, the order in which their concentrations cross their respective thresholds may depend not only on their degradation kinetic parameters but also on the particular storage temperature profile, be it isothermal or non-isothermal. Thus, at least theoretically, the order observed in accelerated storage need not be always indicative of the actual order at colder temperatures, except where the two degradation reactions follow the same kinetic order and their temperature-dependence rate parameter is also the same. This is shown with simulated hypothetical degradation reactions that follow first or zero order kinetics and whose rate constant's temperature-dependence obeys the exponential model. It is also demonstrated with simulated hypothetical Maillard reaction's products whose synthesis rather than their degradation follows pseudo zero order kinetics. The software developed to do the simulations and calculate the thresholds crossing points has been posted on the Internet as a freely downloadable interactive Wolfram Demonstration, which can be used as a tool in storage studies and shelf life prediction. In principle, the methodology can be extended from two to any number of markers.