Arthur A. Teixeira

Mathematical modeling of the thermal degradation kinetics of vitamin C in cupuaçu (Theobroma grandiflorum) nectar

Abstract The thermal degradation kinetics of both components of vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA), were determined in a nectar of Cupuacu (Theobroma grandiflorum) with 25% of pulp and 15% of sugar in water. AA was assayed by HPLC and the results showed that AA degraded into DHAA. A reversible first order model described well the AA degradation data, with an activation energy of 74±5 kJ/mol and k 80 ∘ C =0.032±0.003 min −1 . DHAA kinetic behavior suggested a consecutive first order reaction where DHAA was the intermediate product of AA degradation. A mechanistic model was derived to predict DHAA concentration. Rate constants were replaced by the Arrhenius equation in the model to evaluate the temperature dependence and the kinetic parameters for AA degradation, previously determined, were used. An activation energy of 65±9 kJ/mol and a k80∘C of 0.013±0.003 min −1 were estimated. The present findings will help to predict the best Cupuacu nectar processing conditions that minimize degradation of an important quality factor such as vitamin C.

On-line retort control in thermal sterilization of canned foods

Abstract This paper presents a short review of recent developments toward achieving computer-based intelligent on-line control systems for assuring safety, quality, and process efficiency of thermally processed canned foods. Various approaches based upon real-time data acquisition systems are described, along with alternative approaches based upon the use of calculated correction factors or mathematical models capable of simulating the heat transfer into canned foods under various processing conditions. The various features of each method are discussed along with suggested industry applications that would be appropriate for each method.

Alicyclobacillus acidoterrestris spores as a target for Cupuaçu (Theobroma grandiflorum) nectar thermal processing: kinetic parameters and experimental methods

The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuaçu (Theobroma grandiflorum) pulp and 15% sugar] were determined by the isothermal method (IM), under batch heating, and by the paired equivalent isothermal exposures (PEIE) method, under non-isothermal continuous conditions. The isothermal experiments were repeated three times, every 4 months, with the same spore suspension kept frozen between experiments. The aging of spores, under frozen storage, seemed to produce a notorious increase in the z-value from experiment to experiment: Experiment 1 (z = 7.8 +/- 2.6 degrees C, D(95 degrees C) = 5.29 +/- 0.96 min), Experiment 2 (z = 22 +/- 5 degrees C, D(95 degrees C) = 5.99 +/- 0.63 min), and Experiment 3 (z =29 +/- 10 degrees C, D(95 degrees C) = 3.82 +/- 0.48 min). The evaluation of the kinetic parameters by the PEIE method was carried out in parallel with Experiment 3, with the same aged spores, and the results (z = 31 +/- 6 degrees C, D(95 degrees C) = 5.5 +/- 1.2 min) were close to the ones obtained in this experiment. From this work, it seems that the PEIE method can also be applied to evaluate the reduction parameters of a spore-forming microorganism, and in a more realistic way, since the continuous system eliminates the errors caused by come-up and cool-down times (CUT and CDT) that are unavoidable in isothermal experiments. Therefore, when designing a thermal process for a continuous system, the PEIE method should be used, or the chances are that the process would be underdesigned, risking that the desired level of spore inactivation would not be achieved. An optimization of the thermal processing conditions was next performed for Cupuaçu nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 degrees C) only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 degrees C will ensure a safe product and retain 98.5% of the original ascorbic acid. Therefore, if A. acidoterrestris is considered as the target microorganism, the nectar should undergo an aseptic high temperature short time principle (HTST) process to achieve a 5D reduction in this acidophilus spore former. However, if the hot-fill-and-hold pasteurization process is preferred, the product should be fortified with ascorbic acid.

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Comparison of capillary and test tube procedures for analysis of thermal inactivation kinetics of mold spores.

Characteristics of capillary and test tube procedures for thermal inactivation kinetic analysis of microbial cells were studied for mold spores. During heating, capillaries were submerged in a water bath and test tubes were held with their caps positioned above the level of the heating medium. Thermal inactivation curves of Aspergillus niger spores in capillaries at around 60 degrees C consisted of a shoulder and a fast linear decline, whereas curves in test tubes consisted of a shoulder, a fast linear decline, and a horizontal tail. There were no significant differences in values of the rate and the delay of fast declines in curves between the procedures. Some experiments were done to clarify the cause for tailing with test tubes. There were no tails with test tubes whose inner walls were not contaminated by A. niger spores, suggesting that tails arise from A. niger spores contaminating the inner walls of test tubes. Temperature of the inner wall at the level of a heating medium was lower than that of the medium. Further, there were no tails for test tubes submerged in the heating medium. These results showed that the reason for survival of contaminants on the upper wall of test tubes was that cells were not subjected to sufficient inactivation temperature. Finally, thermal inactivation curves of A. niger spores in capillaries at various constant temperatures were studied. Curves consisted of a shoulder and a fast linear decline at 57 degrees C and above, whereas curves at below 57 degrees C consisted of a shoulder, a fast linear decline, and a sloping tail.

Thermophilic Anaerobic Digestion of Sugar Beet Tailings

Tailings from sugar beet processing are currently managed by landfilling or land application. As an alternate option, beet tailings were anaerobically digested at thermophilic temperatures. It was found that tailings contain a large fraction of water-soluble organic matter, approximately 0.6 g COD (chemical oxygen demand) per g VS (volatile solids), that inhibited initiation of methanogenesis. This work showed that methanogenesis can be initiated if the solubilized material is removed. By using a process that involves first leaching and removal of solubilized matter followed by flooding the bed with digested leachate containing acclimatized inoculum, anaerobic digestion of the tailings was successfully accomplished. Most of the methane potential remaining in solids was generated within a week. The methane yield of tailings was estimated to be 295 L at standard temperature and pressure (STP) per kg VS, of which 50% to 60% was from the readily solubilized organic matter. A volume reduction of 70% to 80% was achieved, and approximately 60% of dry matter and 75% of volatile solids were degraded. All the volatile organic acids (acetic, propionic, and butyric) after an initial accumulation were degraded to low levels in all experiments. Individually, 53.3% of crude protein, 88.3% of nonfibrous carbohydrates, 81% of hemicellulose, 31.5% of lignin, and 64.6% of cellulose were either degraded or solubilized. It was also shown that a robust inoculum for sustained thermophilic anaerobic digestion can be cultured by initially flooding a bed of tailings with a buffer solution. The inoculum thus developed was robust enough to carry out successive balanced digestion of several batches of tailings.

Temperature and Concentration Dependence of Heat Capacity of Model Aqueous Solutions

Abstract Heat capacities of binary aqueous solutions of different concentrations of sucrose, glucose, fructose, citric acid, malic acid, and inorganic salts were measured with a differential scanning calorimeter in the temperature range from 5°C to 65°C. Heat capacity increased with increasing water content and increasing temperature. At low concentrations, heat capacity approached that of pure water, with a less pronounced effect of temperature, and similar abnormal behavior of pure water with a minimum around 30°C–40°C. Literature data, when available agreed relatively well with experimental values. A correction factor, based on the assumption of chemical equilibrium between liquid and gas phase in the Differential Scanning Calorimeter, was proposed to correct for the water evaporation due to temperature rise. Experimental data were fitted to predictive models. Excess molar heat capacity was calculated using the Redlich–Kister equation to represent the deviation from the additive ideal model.

Kinetic Parameters Estimation for Ascorbic Acid Degradation in Fruit Nectar Using the Partial Equivalent Isothermal Exposures (PEIE) Method under Non‐Isothermal Continuous Heating Conditions

With the purpose of testing the Paired Equivalent Isothermal Exposures (PEIE) method to determine reaction kinetic parameters under non‐isothermal conditions, continuous pasteurizations were carried out with a tropical fruit nectar [25% cupuaçu (Theobroma grandiflorum) pulp and 15% sugar] to estimate the ascorbic acid thermal degradation kinetic parameters. Fifteen continuous thermal exposures were studied, with seven being cycled. The experimental ascorbic acid thermal degradation kinetic parameters were estimated by the PEIE method (Ea = 73 ± 9 kJ/mol, k80°C = 0.017 ± 0.001 min−1). These values compared very well to the previously determined values for the same product under isothermal conditions (Ea = 73 ± 7 kJ/mol, k80°C = 0.020 ± 0.001 min−1). The predicted extents of reaction presented a good fit to the experimental data, although the cycled thermal treatments presented some deviation. In addition to being easier and faster than the Isothermal method, the PEIE method can be a more reliable method to estimate first‐order reaction kinetic parameters when continuous heating is considered.

Impact of Overall and Particle Surface Heat Transfer Coefficients on Thermal Process Optimization in Rotary Retorts

This study attempts to examine the significance of recent research that has focused on efforts to estimate values for global and surface heat transfer coefficients under forced convection heating induced by end-over-end rotation in retorting of canned peas in brine. The study confirms the accuracy of regression analysis used to predict values for heat transfer coefficients as a function of rotating speed and headspace, and uses them to predict values over a range of process conditions, which make up the search domain for process optimization. These coefficients were used in a convective heat transfer model to establish a range of lethality-equivalent retort temperature-time processes for various conditions of retort temperature, rotating speed, and headspace. Then, they were coupled with quality factor kinetics to predict the final volume average and surface quality retention resulting from each process and to find the optimal thermal process conditions for canned fresh green peas. Results showed that maximum quality retention (surface and volume average retention) was achieved with the shortest possible process time (made possible with highest retort temperature), and reached the similar level in all cases with small difference between surface and volume average quality retention. The highest heat transfer coefficients (associated with maximum rotating speed and headspace) showed a 10% reduction in process time over that required with minimum rotating speed and headspace. The study concludes with a discussion of the significance of these findings and degree to which they were expected.

Temperature and Concentration Dependence of Density of Model Liquid Foods

Abstract Density of binary solutions and combinations of sucrose, glucose, fructose, citric acid, malic acid, pectin, and inorganic salts were measured with an oscillating tube density meter in the temperature range from 10° to 60°C, at varying concentrations. Density can be predicted with accuracy better than 5 × 10−5 g cm−3 using predictive equations obtained by fitting the experimental data. Available literature values agreed well with experimental data. Relations for the excess molar volume of these solutions were derived in terms of mole fraction and temperature. A thermodynamic model for the volumetric analysis of multicomponent aqueous solutions containing electrolyte and non‐electrolyte compounds was also proposed. These models can be used for prediction of density of liquid food systems, specially fruit juices and beverages, based on composition and temperature, with high accuracy and without elaborate experimental work.