Browsing by Author "Silva, Filipa M."
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- Alicyclobacillus acidoterrestris spores as a target for Cupuaçu Theobroma grandiflorum) nectar thermal processing: Kinetic parameters and experimental methodsPublication . Vieira, Margarida C.; Teixeira, Arthur A.; Silva, Filipa M.; Gaspar, Nelma; Silva, Cristina L.M.The kinetic parameters of thermal inactivation of a spore former, Alicyclobacillus acidoterrestris, in a tropical fruit nectar [25% of Cupuac u (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 = 7.8F2.6 jC, D95 jC = 5.29F0.96 min), Experiment 2 (z=22F5 jC, D95 jC = 5.99F0.63 min), and Experiment 3 (z=29F10 jC, D95 jC = 3.82F0.48 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=31F6 jC, D95 jC = 5.5F1.2 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 Cupuac u nectar, considering a 5D reduction in A. acidoterrestris spores. If a pasteurization process is considered, the conditions that ensure safety (9 min at 98 jC) only allow a 55% retention of ascorbic acid (AA). If sterilization is considered, 8 s at 115 jC 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.
- Colour changes in thermally processed cupuaçu (Theobroma grandiflorum) puree: critical times and kinetics modellingPublication . Silva, Filipa M.; Silva, Cristina L. M.Colour changes in thermally treated cupuaçu (Theobroma grandiflorum) fruit puree were modelled mathematically. Isothermal experiments in the temperature range of 80–115 °C were performed and colour was measured by a tristimulus colorimeter. At each temperature total colour difference (TCD*) increased and normalized L* decreased with processing time, both following a power law model. The power of the model was temperature-dependent and described by the Arrhenius law. To estimate the model constants, a one-step non-linear regression was performed on all data. Activation energies of 31 and 36 kJ/mol were determined for TCD* and normalized L*, respectively. These results should prove useful in the design of pasteurization processes which minimize colour changes in cupuaçu puree
- Establishing a new pasteurization criterion based on Alicyclobacillus acidoterrestris spores for shelf-stable high-acidic fruit productsPublication . Silva, Filipa M.; Gibbs, Paul; Silva, Cristina L. M.
- Thermal inactivation of Alicyclobacillus acidoterrestris spores under different temperature, soluble solids and pH conditions for the design of fruit processesPublication . Silva, Filipa M.; Gibbs, Paul; Vieira, Margarida C.; Silva, Cristina L. M.Alicyclobacillus acidoterrestris, a thermoacidophilic, non-pathogenic and spore-forming bacterium has been detected in several spoiled commercial pasteurised fruit juices. A. acidoterrestris spores, besides being resistant to the pasteurisation treatment conditions normally applied to acidic fruit products, can germinate and grow causing spoilage. Therefore, this microorganism was suggested as the target to be used in the design of adequate pasteurisation processes. The objectives of this work were to investigate the influence of temperature (T: 85–97°C), total soluble solids (SS: 5–60°Brix or % by weight) and pH (2.5–6.0) on D-values (decimal reduction time) of Alicyclobacillus acidoterrestris (type strain, NCIMB 13137) spores, and to fit a model using response surface methodology. A central composite face-centred experimental design was used, and the response, D-value determined in malt extract broth, ranged between 0.498±0.045 and 94.9±6.7 min. Within the factor ranges studied, temperature was the parameter that most affected the D-value. Following this was the SS and, lastly, the pH value. A linear decrease in D-value was observed with decreasing SS and pH, and a non-linear decrease in D-value was noticed with increasing temperature. A second order polynomial was successfully fitted to the data (R2=0.98). In general, D-values measured in real fruit systems, such as orange, apple and grape juices, blackcurrant concentrates, cupuaçu (exotic fruit) extract and orange juice drink, were higher than those predicted by the malt extract broth model. This result emphasises the importance of experimental validation of any model-derived process.