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Front-Face Fluorescence Measurement of Photosensitizers and Lipid Oxidation Products During the Photooxidation of Butter

A. Veberg^*,,1, E. Olsen^*,, A. N. Nilsen^* and J. P. Wold^*

^* Matforsk AS, Norwegian Food Research Institute, Osloveien 1, NO-1430 Ås, Norway
Norwegian University of Life Sciences, Department of Chemistry, Biotechnology, and Food Science, PO Box 5003, NO-1432 Ås, Norway

¹ Corresponding author: annette.veberg{at}matforsk.no

This paper shows that fluorescence spectroscopy can measure both degradation of photosensitizers and formation of lipid oxidation products in light-exposed butter. The photosensitizers were already notably degraded after 4 h of light exposure, whereas fluorescent lipid oxidation products were detected after 5 d. The fluorescence measurements were highly correlated with sensory assessments of acidic and rancid flavor. Photosensitizer degradation is therefore a promising indirect indicator of the onset of lipid oxidation in butter. Sensory analysis and measurement of peroxide value showed that the level of lipid oxidation was significantly higher for butter stored in air compared with butter stored in nitrogen (N₂). This might be explained by the formation of singlet oxygen from direct photooxidation and type II photosensitized oxidation. Addition of the singlet oxygen quencher ß-carotene reduced the rancid flavor intensity in the air and N₂ packages from 9.0 to 4.9 and from 6.5 to 4.7, respectively. Results indicate that lipid oxidation in the butter stored in N₂ was mainly caused by type I photosensitized reactions, because addition of ß-carotene had little effect on the rancid flavor intensity.

Key Words: fluorescence spectroscopy • photooxidation • butter • photosensitizer