Purification Of Sweet Corn Lipoxygenase And Its Relationship With Flavor

Lipid oxidation is one important factor that affects the off-flavor development in sweet corn during frozen storage, and Lipoxygenase (LOX) is a key enzyme that would cause lipids to be oxidized. In order to discuss the relationship between LOX and the flavor of sweet corn, LOX was separated and purified from fresh sweet corn, and then its characteristics and thermal inactivation were studied, meanwhile the changes of lipid oxidation and LOX activity were pursued during frozen storage. The results and conclusions are as follows:1. Separation and purification of LOX from sweet cornLOX was purified from fresh sweet corn, the process included preparation of crude enzyme powder, precipitation with ammonium sulfate, dialysis, anion-exchange chromatography and gel filtration chromatography. The ultimate specific activity reached480.95U/μg, the purification factor was27.85, and the recovery rate was5.53%. The protease was a single band in SDS-PAGE, and its molecular weight was93.14kDa.2. Characterization and thermal inactivation kinetics of LOX from sweet cornThe optimum temperature and pH of sweet corn LOX were30℃and7.5, respectively. LOX remained relatively stable at pH6.0. The enzymatic activity was stimulated by Ca2+, K+, Mn2+, but was inhibited by Fe3+, Cu2+, complexing agents and sulfhydryl reagents. The reactive kinetics were in accordance with Michaelis equation; Km and Vmax were found to be4.37mmoi/L and13.00U/min, respectively. Thermal inactivation of LOX could be described by a first order kinetic model, and activation energy was further calculated to be116.39±0.52kJ/mol.3. Lipoxygenase acitivity and flavor in sweet corn during frozen storageAfter the addition of purified LOX and linoleic acid to analog enzymatic oxidation, exogenous LOX had little effect on the production of volatile components in the oxidation products, while linoleic acid caused a higher amount of typical volatile components. Correlation analysis showed that in the blanched sweet corn, LOX activity was in positive correlations with the contents of linoleic acid and linolenic acid, but in negative correlations with fatty acid value, peroxide value and hexanal content, and the non-blanched sweet corn did not show any regularity. These changes of LOX activity and lipid oxidation index indicated that LOX played an important role in lipid oxidation during frozen storage and led to the generation of bad flavor in sweet corn. However, enzyme inactivation by blanching slowed down the enzymatic oxidation of lipids to some extent and can ensure the corn has high flavor quality.