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Advisor(s)
Abstract(s)
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.
Description
Keywords
Alicyciclobacillus acidoterrestris spores Inactivation kinetics PEIE method Isothermal method Cupuac u (Theobroma
Pedagogical Context
Citation
VIEIRA, Margarida C...[et al] - processing: Kinetic parameters and experimental methods. International Journal of Food Microbiology. ISSN 0168-1605. Vol. 77 (2002), p. 71ā 81
Publisher
Elsevier