Title: Inactivation kinetics and photoreactivation of vegetable oxidative enzymes after UV-C processing Authors
|Sampedro, Fernando -|
Submitted to: Innovative Food Science and Emerging Technologies
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 6, 2014
Publication Date: N/A
Interpretive Summary: Oxidative enzymes are responsible for detrimental quality changes in fruit juices. A study was conducted to evaluate the synergic effects of temperature and ultraviolet C (UV-C) on the enzyme activities in lipids. Modeling of enzyme activities in response to difference temperatures and UV-C dose demonstrated that the combination of mild heating and UV-C treatment was an effective processing strategy to reduce the activities of the enzymes. The information will be helpful for the industry to design UV-C treatment apparatus for the pasteurization of liquid foods.
Technical Abstract: The inactivation kinetics of lipoxygenase (LOX), peroxidase (POD) and polyphenoloxidase (PPO) in phosphate buffer (pH 4.0 and 7.0) treated by combined thermal (25-65 C) and UV-C (1-10 min) processes were fitted using a traditional first-order kinetics model and the Weibull distribution function. For complete inactivation, a treatment at 65 C for 7.5-10 min for LOX and POD and PPO at pH 7.0 and 45 C for 5-7.5 min for POD and PPO at pH 4.0 was necessary. Deviations from the log-linear behavior were observed by the appearance of shoulders, tails or both (sigmoidal). The traditional log-linear model failed to characterize the UV treatment effectively due to the under- and overestimation of enzyme inactivation. The Weibull model was better able to explain the nature of the UV treatment. The extent of enzyme inactivation was less in orange juice due to the greater absorbance of the juice in the UV-C range. In general, activities of residual enzymes after UV-C treatment did not recover after storage for 24 h at refrigeration conditions with or without light exposure, indicating that the enzyme inactivation by UV-C was irreversible. The proposed combination of thermal and UV-C processing was able to improve the stability of the treated samples.