Continuous-Flow Microwave Inactivation Kinetics of Pectin Methyl Esterase in Orange Juice

Abstract

The use of microwave energy as an alternative to conventional continuous‐flow pasteurization of orange juice was explored. One advantage of microwave heating is obvious: it can prevent surface fouling of heat exchanger, due to prevailing higher surface temperature. Microwave heating may also have the potential for intensified enzyme inactivation which is explored in this study. To elucidate conditions suitable for continuous pasteurization of orange juice, a microwave heating system was designed using a domestic microwave oven (700W) under a full power operation. The residence time of the juice in the heating coil in the microwave oven was dependent on the juice flow rate and dimensions of the heating tube. Based on time‐temperature profile and predetermined enzyme inactivation kinetics, the effectiveness of microwave heating (come‐up) was evaluated. The PME decimal reduction time for microwave heating were ∼38, 12, 4.0 and 1.3 s at 55, 60, 65 and 70C, respectively, as compared with ∼150 and 37s at 60 and 70C under conventional heating, respectively. Microwave heating is, therefore, substantially more effective in inactivating PME in orange juice than conventional method.

Microwave material processing—a review

“…209 In another report, an increase in the rate constant for the ring-opening polymerization of caprolactone by microwaves was found to be induced not only by thermal conditions but also by the athermal microwave effect. 263 Microwaves were used for the inactivation of pectin methylesterase in orange juice 147 and the destruction of spoilage microorganisms in apple juice. 148 It was observed that at 50-65 C the death rates of microorganisms exposed to microwaves were higher than those obtained in conventional heat sterilization at the same temperature.…”

“…It was found that microwave heating was significantly faster than the conventional thermal heating mode and provided some contributory nonthermal effects. 147 Specific spoilage microorganisms in apple juice could be destroyed faster under continuous flow microwave heating than under conventional heating conditions. 148 Heddleson and Doores 149 investigated the variables influencing temperature and bacterial destruction in foods with microwave heating and they reported that the microbes were inactivated by microwaves solely due to thermal effects.…”

Inactivation kinetics of polyphenol oxidase and peroxidase in green coconut water by microwave processing

“…First order reaction kinetics was assumed for enzyme inactivation during microwave treatment (Tajchakavit and Ramaswamy, 1997;Tajchakavit et al, 1998;Soysal and Sö ylemez, 2005), therefore the predicted residual activity for each experimental run can be calculated from Eq. (4) if kinetic parameters D T ref and z are known.…”

Peroxidase and polyphenol oxidase thermal inactivation by microwaves in green coconut water simulated solutions

“…First estimates of D values can be calculated based on the total residence time of the product in the microwave cavity, and from D values a first estimate of z value is obtained. Correction of heating times and calculation of D and z can then be repeated to get convergence of D and z values (Tajchakavit & Ramaswamy, 1997;Tajchakavit, Ramaswamy, & Fustier, 1998;Toledo, 1991).…”