The Use of Proton Transfer Reaction Mass Spectrometry Monitoring Oxidative Changes of Fish Oil Ethyl Ester and its Products

Abstract

The aim of this study was to use Proton Transfer Reaction Mass Spectrometry (PTR-MS) to monitor the oxidative changes in fish oil ethyl esters (FOEE) and in microencapsulated FOEE powder. PTR-MS results were first correlated with traditional methods of oxidative analysis.

The PTR-MS is a rapid and sensitive technique that may be able to directly measure volatiles produced by lipid oxidation in complex matrices without requiring any extraction procedure. In the first part of this study FOEE were stored in glass bottles (10mL oil: 90mL headspace) in the dark at 35°C and sampled over 12 weeks. The changes in the volatile composition above the FOEE were determined by PTR-MS and related to changes in Peroxide Value (PV), ρ-Anisidine Value (AV), Refractive Index (RI) Value and the dielectric properties measured using food oil sensor (FOS). The dominant mass ions detected by PTR-MS were m/z 41, m/z 43, m/z 45, m/z 47, m/z 55, m/z 57 and m/z 59. The mass fragments were tentatively identified from literature as short chain aldehydes, alcohols and esters and PTR-MS was demonstrated to predict the secondary oxidation level of FOEE correlating with AV to monitor shelflife.

In the second part of this study, Spray drying was used for a FOEE microencapsulation study. The ratio of FOEE and Acacia Gum was 1:4. The recovery of total in the powder was 20% and surface oil of the powder particle was 5%. Microencapsulated FOEE powder was stored in glass bottles (10g powder in 100 mL glass bottle) in the dark at 35°C and sampled over 7 weeks. The changes in the volatile composition above the FOEE were determined by PTR-MS and related to the AV of surface oil on FOEE powder. The oxidative changes in the material before spray drying was monitored by headspace monitoring using PTR-MS and the heat damage of spray drying process was assessed by monitoring a model for the heat treatment of FOEE in an oil bath at 120°C with air circulation. The results of this part of study show that headspace composition does not reflect oxidation level of FOEE powder due to some volatile organic compounds (VOC) being lost during spray drying after evaporation from FOEE. There was no significant change in particle size distribution and oxidative stability of FOEE emulsion for the first day after the emulsion was made. The results of FOEE powder trial have shown that microencapsulation by spray drying were not an effective way to protect oxidative stability of FOEE due to the heat damage of FOEE during the spray drying process.