Browsing by Author "Teixeira, A. A."
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Alicyclobacillus acidoterrestris spores as a target for Cupuacu (Theobroma grandiflorum) nectar thermal processing: kinetic parameters and experimental methodsPublication . Vieira, Margarida; Teixeira, A. A.; Silva, F. M.; Gaspar, N.; Silva, C. L. M.The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuaca (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 I (z = 7.8 +/- 2.6 degreesC, D-95 (degreesC) = 5.29 +/- 0.96 min), Experiment 2 (z = 22 +/- 5 degreesC, D-95 (degreesC) = 5.99 +/- 0.63 min), and Experiment 3 (z = 29 +/- 10 degreesC, D-95 degreesC = 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 degreesC, D-95 (degreesC) = 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 Cupuacu nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 degreesC only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 degreesC 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 the 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. (C) 2002 Elsevier Science B.V. All rights reserved.
- Kinetic parameters estimation for ascorbic acid degradation in fruit nectar using the partial equivalent isothermal exposures (PEIE) method under non-isothermal continuous heating conditionsPublication . Vieira, M. M. C.; Teixeira, A. A.; Silva, C. L. M.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% cupuacu (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 (E-a = 73 +/- 9 kJ/mol, k(80 degreesC) = 0.017 +/- 0.001 min(-1)). These values compared very well to the previously determined values for the same product under isothermal conditions (E-a = 73 +/- 7 kJ/mol, k(80 degreesC) = 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.
- Mathematical-modeling of the thermal-degradation kinetics of vitamin-c In cupuaçu (theobroma-grandiflorum) nectarPublication . Vieira, M. M. C.; Teixeira, A. A.; Silva, C. L. M.The thermal degradation kinetics of both components of vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA), were determined in a nectar of Cupuacßu (Theobroma grandi¯orum) 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 ®rst order model described well the AA degradation data, with an activation energy of 74 5 kJ/mol and k80 C 0:032 0:003min ÿ1. DHAA kinetic behavior suggested a consecutive ®rst 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 ÿ1 were estimated. The present ®ndings will help to predict the best Cupuacßu nectar processing conditions that minimize degradation of an important quality factor such as vitamin C.