Understanding and measuring photooxidation by fluorescence spectroscopy

Light is known to initiate oxidation processes resulting in discoloration and formation of off-flavours in foods. Milk and milk products are particularly sensitive to light, and the photo-initiated reactions affect not only the sensory quality, but may also lead to formation of toxic compounds in certain products and to degradation of nutrients.

Riboflavin has until recently been regarded as the active photosensitizer in dairy products. Recently, however, we used front face fluorescence spectroscopy to monitor the photooxidation directly in intact cheese. We then discovered that cheese, as well as other dairy products, contain at least five other light sensitive substances. In close collaboration with the Photo Dynamic Therapy group at The Norwegian Radium Hospital, we identified the peaks to originate from protoporphyrin, hematoporphyrin, possibly chlorophyll a, as well as two non-characterised porphyrins, all of them powerful photosensitizers.

Several experiments have later shown that the photodegradation of these substances correlates very well with formation of sensory assessed photooxidation. Especially degradation of protoporphyrin seems to be a reliable marker for early photooxidation in cheese and butter. The degradation of these photosensitizers can be monitored directly in the product by front face fluorescence spectroscopy. A valuable tool for this monitoring is multivariate curve resolution on emission-excitation matrices (EEMs) by PARAFAC. This approach enables very efficient and precise analysis of these complex spectral data. Light exposure experiments in combination with fluorescence spectroscopy and PARAFAC is currently being used for evaluation of packaging and retail conditions, as well as for increasing our understanding of fundamental properties concerning photooxidation.



Figure 1: Sensory scores for oxidized flavour measured on Swiss-like cheese exposed to light of seven different colours and darkness.


Figure 2: Fluorescence emission spectra from Swiss-like cheese samples stored under light of different colours. Colours of the spectra refer to the light colour used for each storage condition. Spectrum from cheese stored in the dark is black. Spectrum from cheese with transparent filter (white light) is gray.



PARAFAC excitation loadings PARAFAC emission loadings

Staff
Jens Petter Wold
Annette Veberg
Frank Lundby


Collaboration
Professor Johan Moan, Photo Dynamic Therapy group at The Norwegian Radium Hospital
Professor Rasmus Bro, Copenhagen University

Financial support
Matforsks strategical research programme:
Effective assessment of food quality by rapid spectroscopic and sensor techniques
Project period: 2005-2008
Project leader: Jens Petter Wold
Financed by: Norwegian Agricultural Authority

Understanding and measuring photooxidation by fluorescence spectroscopy
Project period: 2005-2008
Project leader: Jens Petter Wold
Financed by: Norwegian Research Council

Publications
Wold, J.P, Jørgensen K, Lundby F. 2002. Nondestructive measurement of light induced oxidation in dairy products by fluorescence spectroscopy and imaging. J Dairy Sci. 85: 1693-1704.

Wold JP, Veberg A, Nilsen A, Juzenas P, Iani V, Moan J. 2005. The role of naturally occurring chlorophyll and porphyrins in light induced oxidation of dairy products. A study based on fluorescence spectroscopy and sensory analysis. Int. Dairy Journal 15:343-353.

Wold JP, Veberg A, Nilsen AN. Influence of storage time and color of light upon photooxidation in cheese. A study based on sensory analysis and fluorescence spectroscopy. Int. Dairy Journal. 16: 1218-1226.

Andersen CM, Wold JP, Mortensen G. 2005. Light-induced changes in semi-hard cheese determined by fluorescence spectroscopy and chemometrics. Int. Dairy Journal 16: 1483-1489.

Wold, J.P., Bro, R., Veberg, A., Lundby, F., Nilsen, A.N., Moan, J. 2006. Active photosensitizers in butter detected by fluorescence spectroscopy and multivariate curve resolution. Agricultural and Food Chemistry, Vol 54, pp 10197-10204.

Veberg A, Sørheim O, Moan J, Iani V, Juzenas P, Nilsen AN, Wold JP. 2006. Mapping of lipid oxidation and porphyrins in high oxygen modified atmosphere and vacuum packed minced turkey and pork meat by fluorescence spectra and images. Meat Sci. 73: 511-520

Veberg, A., Olsen, E., Nilsen, A.N., Wold, J.P. Front face fluorescence measurement of photosensitizers and lipid oxidation products during photooxidation of butter. J Dairy Sci. 90:2189-2199



Links
Effective assessment of food quality by rapid spectroscopic and sensor techniques
Rasmus Bro, master of PARAFAC
Professor Johan Moan, Radium hospital

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