Study of enzyme inactivation in the processing of green coconut water by focused microwave technology

Abstract

In the processing of liquid foods, continuous heat treatment is intended for inactivating microorganisms and enzymes that compromise the safety and product quality. In the case of green coconut water, enzymes polyphenoloxidase (PPO) and peroxidase (POD) exhibit high thermal stability and the sensorial quality of the product (color and taste) is sensitive to high temperatures, making it challenging to process this product without the addition of preservatives. The emerging technology of continuous heating by focused microwaves is promising for promoting rapid volumetric heating without surface overheating and with a non-thermal effect on enzyme inactivation. Thus, the objective of this work is to study the inactivation of PPO and POD in green coconut water to determine the respective kinetics in conventional and microwave heating, seeking identification of non-thermal effects, with validation of the obtained conditions in a pilot scale equipment. To study the kinetics, batch tests will be performed in immersion thermal baths and in a chemical synthesis mini-reactor by focused microwaves with fiber optic temperature record. The enzymatic activity will be evaluated by spectrophotometric methods. Kinetic models for prediction of residual activity will be adjusted based on recorded temperature history using a non-linear optimization method linked to the numerical integration of lethality, thus avoiding the simplifying assumption of constant temperature. Based on the results of the batch runs, processing conditions compatible with the pilot scale equipment with heating by focused microwaves will be defined and tested for obtaining an adequate level of residual enzymatic activity. It is expected that this research will allow the elucidation of the non-thermal effects of microwaves on the inactivation of the enzymes of green coconut water and assessing the feasibility of innovative technology for the processing of this product. (AU)