Identification of a ripening-related lipoxygenase in tomato fruit as blanching indicator enzyme

To learn how the protein stability may be correlated to the nutritional quality in tomato (Solanum lycopersicum Mill.) fruit during processing, a 97-kDa protein closely related to ripening and processing quality was pursued in this study. The 97-kDa protein was separated from tomato fruit, identified as lipoxygenase (LOX) by employing MALDI-TOF mass spectrometry and immunoprecipitation. Using the 97-kDa-specific antibodies to determine thermal stability had shown that the 97-kDa LOX of tomato fruit was undetectable after incubating the extract at 70 °C for 10 min, or heating the fruit at 60 °C for 10 min. The changes in 97-kDa LOX by immunoblotting assay are coordinated with the changes in activity of LOX in the fruit under various conditions. The 97-kDa LOX rather than peroxidase is better correlated to the changes of quality in tomato fruit after blanching treatment. The 97-kDa LOX in different tissues from breaker and red-ripe tomato fruit were found to be maximally accumulated in the pericarp of red-ripe tomato fruit. These results suggested that the 97-kDa LOX in tomato fruit is a ripening-related LOX and can be used as an indicator enzyme in tomato processing.