Kinetics Of Ascorbic Acid Research Articles

DRYING CHARACTERISTICS AND QUALITY OF RED PEPPER SLICES UNDER HOT AIR FOLLOWED BY MICROWAVE FINISH DRYING

Red pepper slices were subjected to hot air, microwave and hot air followed by microwave finish drying. Hot air followed by microwave finish drying decreased the drying time required when compared to drying with hot air drying. Among the five thin layer drying models that were used to fit the experimental data, Page and Modified Page models gave the highest correlation coefficient, lowest root mean square error, and reduced chi-square, thus indicating that Page and Modified Page models best described the hot air drying of red pepper slices. In this study, ascorbic acid degradation and color changes during drying were also investigated. In the drying process at 65ºC for 9 hours, ascorbic acid content decreased to 330.94±1.45 mg/100g dry matter after 8 hours. After 8 hours, no ascorbic acid was found. Moreover, the kinetics of ascorbic acid and color changes of red pepper slices, due to drying by hot air drying were studied. It was confirmed that ascorbic acid degradation followed first order kinetics. The results indicate that hot air followed by microwave finish drying may be an alternative method for the drying of red pepper slices since it provides good quality product in shorter time.

Multilevel modeling in food science: A case study on heat-induced ascorbic acid degradation kinetics

Characterization of variation of experimental results is achieved by repeating experiments. Frequently, results are averaged before data are analysed but that may not be the best practice because valuable information is then lost. Three other ways to analyze repetitions are: (1) each experiment is analyzed on its own (no pooling of data), (2) all experiments are analyzed together in one go (complete pooling), (3) data are analyzed together while allowing for similarities as well as differences in the result (partial pooling). Multilevel modeling uses partial pooling by partitioning variance over more than one level. Level 1 consists of the measurements themselves; higher levels consist of groups or clusters of measurements (repetitions, experiments at various temperatures, at various pH values, etc.) and parameters are analyzed both at the population and at the group/cluster level.The approach is applied to a case study in which heat-induced isothermal degradation of ascorbic acid was studied with 15 repetitions in an aqueous solution, making it a two-level study. The data were analyzed using averaging and complete pooling, complete pooling without averaging, no-pooling at all, and partial pooling. The kinetic model was established by letting the data decide about the order of the reaction, while this was compared to a model where the order was fixed at 1 (first-order model). Results show that both averaging with complete pooling, as well as complete pooling without averaging, strongly underestimate variation. The no-pooling technique overestimates variation, while partial pooling partitions variation over the levels and thus gives a better impression of the variation involved. The kinetics of ascorbic acid appear to be subject to strong variation when each experiment is considered separately because it is a compound that is very sensitive to all kinds of experimental conditions. With multilevel modeling it appeared to be possible to characterize the uncertainties involved much better than with single level modeling. A Bayesian analysis was performed, in which parameters are allowed to be variable, which is useful because multilevel modeling leads to characterization of variation of parameters. The Bayesian method allows to visualize the posterior distribution of parameters, thereby giving more insight in their behaviour. Also, a Bayesian analysis focuses more strongly on predictive accuracy of models, including multilevel models. The predictive accuracy of 4 models describing the same ascorbic acid data was compared and the multilevel model with reaction order estimated from the data performed by far the best in this regard. The pros and cons of multilevel modeling are discussed and it is concluded that multilevel modeling is to be preferred whenever the data allow to perform such an analysis.

KINETICS OF ANTIOXIDANTS DEGRADATION AND QUALITY CHANGES OF CITRON (Citrus medica) FRUIT JUICE CONCENTRATE DURING STORAGE

The aim of the study was to develop fruit juice concentrate from Citron and its kinetic evaluation during storage at 10 ºC, 25 ºC and 40 ºC respectively, for 12th week. The effect of different temperatures on the quality of the juice concentrate was also investigated. The concentration of ascorbic acid in the juice concentrate was monitored after every week of storage. The results showed that degradation kinetics of ascorbic acid during storage was followed by the first-order kinetics. The degradation rates of ascorbic acid during storage at 10 ° C, 25 °C and 40 °C were obtained as 2.27 ± 0.24, 2.46 ± 0.31 and 2.56 ± 0.34 1/week respectively. The higher degradation rate was observed at 40 °C storage temperature. Temperature-dependent rate constants of ascorbic acid of citron juice concentrate was obeyed the Arrhenius relationship with higher R2 values as 0.96. Total antioxidant degradation was also high at higher storage temperatures. The amount of total phenolic content was decreasing at the first few weeks of storage, but later period of storage it was in gradually increasing trend. The storage study demonsrated that ascorbic acid, total polyphenol and antioxidant activity were not degraded at lower temperature after 12th week.

Kinetics of ascorbic acid thermal degradation in Valencia orange juices and evaluation of its shelf life

Ascorbic acid is a well-known natural antioxidant which is widely distributed in nature, especially in green plants. Its traditionally known sources are citrus fruits like orange. This vitamin acts as an efficient radical inhibitor and it has been used as a food additive. Moreover, it presents antioxidant activity and contributes for the prevention of certain types of cancer. Ascorbic acid is also used as an index of nutritional quality of fruits and vegetables, due to its sensibility to different kinds of degradation in food processing and subsequent storage. Thus, the study of ascorbic acid degradation kinetics is important to raise information that allows estimating the quality changes that occur during the storage of food products. The purpose of this research was to evaluate the thermal degradation kinetics of ascorbic acid in Valencia orange juices and to quantify the effect of water activity on its rate of loss upon storage. Ascorbic acid content was determined by titration with 2,6 dichlorophenol indophenol. Its degradation as a function of storage time was studied at different temperatures during a period of 14 days of storage. Reaction constant rates (k) and the order of reaction (n) were determined through regression analysis of experimental data. Higher coefficient of determination (R2) indicated that a first-order reaction model fits closely well to data obtained in this study. In general, it was observed that increasing temperature and water activity led to increasing losses of ascorbic acid. A direct equation for the estimation of the shelf life of the juice with respect to ascorbic acid losses at any specified temperature and degradation rate has been derived.

Degradation kinetics of ascorbic acid in home-made juices.

Degradation kinetics of ascorbic acid in home-made juices.

NONENZYMATIC BROWNING KINETIC REACTION AND ASCORBIC ACID DEGREDATION OF HEAT-TREATED ORANGE JUICE DURING STORAGE

The kinetics of ascorbic acid (AA) degradation and nonenzymatic browning (NEB) of heat-treated single strength orange juice (OJ) over a temperature between 70-95 oC for 2-10 min. and stored under opaque condition at 4 and 20 oC for 2 months have been studied. Analysis of kinetic data by measuring absorbance at 420 nm (A420) suggested a zero-order reaction for NEB, while AA degradation followed a first-order reaction. The temperature dependence of NEB and AA degradation were adequately modeled by the Arrhenius equation. Activation energy of NEB and AA degradation as affected by heat-treatment and storage condition followed the same trend. The obtained results indicate that AA degradation can be evaluated by the intensity of brown colour development of OJ.

Degradation kinetics of ascorbic acid in encapsulated spray-dried honey powder packaged in aluminium laminated polyethylene and high-density polyethylene

ABSTRACTThe present study evaluated the stability of nutritionally rich encapsulated spray-dried honey powders in terms of hygroscopicity, glass transition temperature, total phenolic content, antioxidant activity and ascorbic acid using maltodextrin, gum arabic, and whey protein concentrate as carriers during a storage period of 180 days using high-density polyethylene and aluminium laminated polyethylene as packaging materials at 25°C (room temperature) and 35°C (accelerated temperature). The results revealed that temperature caused a negative influence on the glass transition temperature and stability of ascorbic acid. The kinetics of ascorbic acid degradation followed a first-order reaction with a reaction rate constant dependent on temperature and packaging material. Honey powder developed with whey protein concentrate as carrier agent and stored in aluminium laminated polyethylene pouches at 35°C possessed the highest antioxidant activity and ascorbic acid due to the presence of phenolic compounds in honey, aonla (Emblica officinalis. Gaertn), and basil (Ocimum sanctum) extract. The honey powders stored in aluminium laminated polyethylene pouches showed comparatively better antioxidant properties (total phenolic content, ascorbic acid, and antioxidant activity) and minimum hygroscopicity than the powders stored in high-density polyethylene at both the storage temperatures.

Kinetics of Quality Attributes of Potato Particulates during Cooking Process

Abstract Kinetics of thermal texture softening, color change and loss of ascorbic acid in potato (Solanum tuberosum) were investigated at selected temperature range (70–100°C) and heating time range (0–50 min). Cut samples of potatoes were heated in a constant temperature water bath at various temperatures. Heat-treated samples were evaluated for texture, color and ascorbic acid by use of a texture-testing machine, a color meter and spectrophotometer, respectively. The biphasic first-order model, the fractional conversion model and the simple first-order model were used for fitting experimental data of time dependence kinetics, while the simple first-order model and Arrhenius model were used for temperature dependence kinetics. The results indicated that the biphasic first-order model can match well to the texture softening of potato samples, the fractional conversion model can well describe the kinetics of color, and the simple first-order model can be used for the kinetics of ascorbic acid. The kinetic parameters including decimal deduction time (D), reaction rate (k), temperature dependence (z) and activation energy (E a) were determined by the nonlinear regression method. The correlation matrix between quality attributes including texture properties, color and ascorbic acid loss was developed based on the kinetic models. The results obtained from this study were compared with those previously reported.

Quenching Mechanism and Kinetics of Ascorbic Acid on the Photosensitizing Effects of Synthetic Food Colorant FD&C Red Nr 3

The pH effect on the oxidative stability of ascorbic acid in the presence of food colorant FD&C Red Nr 3 during storage with or without light was investigated. The quenching mechanism and kinetics of ascorbic acid on the FD&C Red Nr 3 photosensitized oxidation in an aqueous system at 25 degrees C were also studied by measuring the degradation of ascorbic acid or depletion of headspace oxygen. Red Nr 3 had no influence on the oxidation of ascorbic acid under dark storage, but accelerated its oxidation rate under light storage. The oxidative stability of ascorbic acid decreased as the pH increased from 4 to 7 under light without FD&C Red Nr 3. The quenching rates of ascorbic acid on the singlet oxygen by measuring the degradation of ascorbic acid in the presence of Red Nr 3 under light storage were 1.53 +/- 0.15 x 10(8), 1.86 +/- 0.25 x 10(8), and 1.19 +/- 0.12 x 10(8) M(-1)S(-1) at pH 4, 5.6, and 7, respectively.

Reversible degradation kinetics of vitamin C in peas during frozen storage

In this study, kinetics of ascorbic acid (AA, 2-oxo-l-threo-hexono-1,4, lactone-2,3 enediol) and dehydroascorbic acid (DHAA, threo-2,3-hexodiulosonic acid-γ-lactone) were studied in blanched and unblanched peas during frozen storage using a first order reversible consecutive reaction model. The time-dependent changes for both AA and DHAA were strongly correlated with the kinetic model described here. Blanching resulted in 19% of reduction in k 1 value (AA degradation rate constant) as compared with unblanched peas (0.227/month±5.43×10−3/month). The regeneration rate constant of AA (k 2) increased approximately 26 folds for blanched peas when compared to unblanched peas (0.0114/month±1.04×10−3/month). Rate constant (k 3) for the conversion of DHAA into 2,3­diketogulonic acid (DKGA) in blanched peas decreased approximately 31 folds by blanching treatment. This kind of kinetic analysis may be used for better understanding the effects of processing and storage conditions on vitamin C.

Degradation Kinetics of the Antioxidant Additive Ascorbic Acid in Packed Table Olives during Storage at Different Temperatures

The kinetics of ascorbic acid (AA) loss during storage of packed table olives with two different levels of added AA was investigated. Three selected storage temperatures were assayed: 10 degrees C, ambient (20-24 degrees C), and 40 degrees C. The study was carried out in both pasteurized and unpasteurized product. The effect of pasteurization treatment alone on added AA was not significant. In the pasteurized product, in general AA degraded following a first-order kinetics. The activation energy calculated by using the Arrhenius model averaged 9 kcal/mol. For each storage temperature, the increase in initial AA concentration significantly decreased the AA degradation rate. In the unpasteurized product, AA was not detected after 20 days in samples stored at room temperature and AA degradation followed zero-order kinetics at 10 degrees C, whereas at 40 degrees C a second-order reaction showed the best fit. In both pasteurized and unpasteurized product, the low level of initial dehydroascorbic acid disappeared during storage. Furfural appeared to be formed during storage, mainly at 40 degrees C, following zero-order kinetics.

Ascorbate‐Dehydroascorbate Level and Redox Status in Leaflets of Field‐Grown Soybeans Exposed to Elevated Ozone

The purpose of this study was to examine and compare the kinetics of ascorbic acid (ASC) and dehydroascorbate (DHA) levels and the ASC:DHA redox status in leaflets of field‐grown ozone (O3)‐treated soybean cultivars at various growth stages. From June through September 1995, two soybean cultivars, cv. Essex and cv. Forrest, were grown in the field within four carbon‐filtered (CF), open‐top chambers (average daytime O3 level was 24 nL L−1 air) and four nonfiltered open‐top chambers fumigated with environmentally relevant elevated O3 levels (average daytime O3 level was 58 nL L−1 air). Exposure of cv. Essex to elevated O3 did not reduce mature leaflet area accretion at any growth stage. However, during the vegetative and reproductive stages in O3‐treated cv. Forrest, leaflet area was as much as 21% lower than in control plants. In both cultivars and at all growth stages, these moderately elevated O3 levels did not cause necrosis in the mature leaflets, nor did O3 inhibit CO2 photoassimilation per unit leafl...

DEGRADATION OF ASCORBIC ACID IN DRYING PROCESS -A COMPARISON OF DESCRIPTION METHODS

ABSTRACT The degradation kinetics of ascorbic acid in food products is presented in the paper. Vibrofluidized method of drying was considered. Experiments were carried out for a model substance (silica gel)and agricultural products, namely: fresh green peas, potatoes and cabbage. Experimental data were described by means of three mathematical methods: a multilayer perceptron (MLP) model, a mathematical model of degradation kinetics of ascorbic acid and a hybrid model. The hybrid model connects neural computation with the mathematical model. All approaches provide an excellent process description. In the case of multilayer perceptron, the proposed method is simpler to implement when compared to the mathematical and the hybrid methods.

Double electropolymer modified platinum electrode to follow the kinetic process H 2O 2 + ascorbic acid. Influence of the reaction on amperometric biosensor applications

A Pt electrode modified by a polypyrrole/poly(orthophenylenediamine) bilayer membrane able to entrap large molecules such as glucose oxidase was used to investigate (at 27°C and pH 7) the kinetics of ascorbic acid (AA) oxidation by hydrogen peroxide (H 2O 2 + AA → 2H 2O + DAA) by following the H 2O 2 concentration as a function of time. The largely unmatched rejection characteristics of this device towards AA permitted it to operate even in the presence of high AA H 2 O 2 ratios, e.g. 1000: 1. Under these conditions, pseudo-first-order kinetic constant values ranging from 3.26 × 10 −3 to 4.10 × 10 −3 s −1 were obtained at [AA] = 2 mM and initial [H 2O 2] = 2 μM. The potential influence of the above reaction on sensitivity and reliability of H 2O 2-detecting biosensors in the presence of AA is discussed critically, taking into account also the recent, and sometimes conflicting, literature views on the problem.

Measurement of ascorbic acid kinetics in man using stable isotopes and gas chromatography/mass spectrometry.

The feasibility of studying ascorbic acid kinetics in man using stable isotope-labelled tracers and gas chromatographic (GC) separation followed by mass spectrometric (MS) quantitation was assessed. Preliminary studies with 13C-labelled material showed that although better precision at low levels could be achieved using the GC/combustion/MS technique, consideration of likely enrichments in a human study made the simpler GC/MS method just as suitable. On this basis, a small pilot study of the kinetics in man was carried out. The enrichment of the ascorbic acid in plasma was measured for a 24 h period after oral administration of 13C-labelled material. The results were fitted to a simple three-compartment model and rate constants and pool sizes were deduced. The results obtained are comparable to those obtained in other published studies, from which we conclude that the technique may be useful as a non-invasive method for the assessment of nutritional status in a variety of populations.

Evaluation of a Conduction Heating Food Model for Ascorbic Acid Retention and Color Formation During Thermal Processing

Ascorbic acid retention and color formation studies were carried out using a conduction heating simulated food model in cylindrical containers subjected to heat processing in a steam retort. Operating conditions, at temperatures from 110 to 127°C, were selected to study the influence of various process times/lethalities on the ascorbic acid retention and induced Maillard-type color formation. Ascorbic acid was analysed by a HPLC technique while the formed color was evaluated using a Minolta Chroma Meter. The study indicated that a food model of wetted celite could be used for distribution of ascorbic acid and/or color forming compounds and their subsequent recovery from the medium, both before and after thermal processing. The study also indicated that kinetics of ascorbic acid retention/destruction and color formation were different depending on whether they were tested individually or in mixtures, and the experimental design provided data for the verification of a computer model for predicting nutrient retention under a range of experimental conditions.