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Investigation of thermal and non-thermal effects of focused microwaves on the activity of enzymes of interest in the processing of fruit-based products.

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Author(s):
Tiago Augusto Bulhões Bezerra Cavalcante
Total Authors: 1
Document type: Master's Dissertation
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Escola Politécnica (EP/BC)
Defense date:
Examining board members:
Jorge Andrey Wilhelms Gut; Luiz Alberto Jermolovicius; Kátia Nicolau Matsui
Advisor: Jorge Andrey Wilhelms Gut
Abstract

Thermal pasteurization processes and commercial sterilization are widely used for the processing of fruit-based liquid foods, such as pulp and juice. The exposure to high temperatures causes degradation of compounds related to sensory and nutritional quality. The heating of liquid foods by focused microwaves is an emerging technology that has the advantage of rapid heating; prevents thermal degradation; allows better maintenance of sensory and nutritional attributes; and prevents incrustation. Besides, there is the presence of nonthermal effects on the enzymes inactivation, which are the main targets of thermal processes to such products. However, confirmation of non-thermal effects is still controversial in the scientific literature. Thus, the objective of this research is to investigate thermal and nonthermal effects of microwaves on the inactivation of enzymes polyphenol oxidase (PPO) and peroxidase (POD), which are relevant for the processing of fruit-based products. To eliminate sources of variability, commercial enzymes in potassium phosphate buffer solution were subjected to conventional (immersion bath) and microwave (mini-reactor for microwave chemical synthesis) treatments, with record of temperature history and residual enzyme activity. In addition, the instantaneous power absorbed in each sample under microwave heating was calculated. The kinetic parameters were adjusted by minimizing quadratic errors in first order kinetic models (D-z) with one and two fractions, by Arrhenius and Weibull model. The PPO results allowed for a better adjustment of the Weibull model. The simulation of the parameters at different temperatures allowed the comparison of the heating methods and it allowed the observation of non-thermal effects of microwaves at temperatures above 70 ºC for the inactivation of PPO. In addition, the parameters of the Weibull model in 10 samples were validated for PPO solution with slower heating; the residual enzymatic activities were compared with the activities predicted by the model. Unexpectedly, the results of the POD enzyme were not satisfactory to determine the evaluated models of its inactivation. The POD presented some residual enzymatic activities above 100% for both heating methods, and high thermal resistance. Thus, it was no possible to observe non-thermal effects of microwaves on POD inactivation in this study. (AU)

FAPESP's process: 14/25041-4 - Investigation of thermal and non-thermal effects of focused microwaves on the activity of enzymes of interest in the processing of fruit-based products
Grantee:Tiago Augusto Bulhões Bezerra Cavalcante
Support Opportunities: Scholarships in Brazil - Master