Evaluate the Validity of Two Popular Food Oxidation Markers (Hexanal & Limonene Oxide) in the Dry State

Abstract

In research, it is common to use chemical indicators of oxidation to determine the oxidative state of a food. For example, hexanal formation/content is used to determine if lipids are oxidizing and limonene oxide (LO) serves a similar purpose in monitoring the oxidation of citrus oils. Recent research has shown that hexanal readily reacts with proteins and unpublished work suggests that limonene oxide also may react with proteins. Thus, these traditional indicators of oxidation may be inaccurate for foods that have higher protein levels or very reactive protein. β-Lactoglobulin (BLG) is a major whey protein in bovine milk and is also a prominent protein utilized in the food industry. Additionally, the structure and amino acid sequence of BLG is well characterized, and its molecular weight is appropriate for intact protein analysis. Therefore, BLG was selected as the model protein for this work. This research studied the covalent reactions between BLG and the two popular oxidation markers (hexanal and LO) in the dry state by liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) and to determine the influence of temperature, pH, and water activity on the reactions. Results show that limonene oxide could form covalent bonds with the BLG. Moreover, the reaction rate increases with the increase of storage time, which could make limonene oxide inaccurate as an oxidation marker in food containing high levels of proteins. For hexanal, the increase of the protein adduct is not very significant during storage. Therefore, hexanal still can be considered as a usable oxidation marker for dry foods.This research can help the food industry understand the validity of the two popular oxidation markers, choose better methods for food oxidation analysis, and improve their quality control system.