Active Photosensitizers in Butter Detected by Fluorescence Spectroscopy and Multivariate Curve Resolution

Abstract

In this study, fluorescence excitation and emission matrices and multivariate curve resolution (PARAFAC) were used to detect and characterize active photosensitizers spectrally in butter. Butter samples were packed under high (air) and low oxygen (<0.05%) atmospheres and exposed to violet, green, or red light. Six photosensitizers were found: riboflavin, protoporphyrin, hematoporphyrin, a chlorophyll a-like molecule, and two unidentified tetrapyrrols. By estimation of relative concentrations, we could follow how each sensitizer was photodegraded as function of wavelength, oxygen level, and time. The degradation rate of protoporphyrin, hematoporphyrin, chlorophyll a, and one of the tetrapyrrols correlated well (0.83-0.91) with the formation of sensory measured oxidation. The results suggest that mainly type I photoreactions were responsible for the degradation of photosensitizers in both high and low oxygen atmosphere. Type II photoreactions (generation of singlet oxygen) were involved in the oxidation of butter stored in air. The study shows that PARAFAC modeling of fluorescence landscapes is an excellent tool for studying photooxidation in complex systems.

Light-induced protein and lipid oxidation in cheese: Dependence on fat content and packaging conditions

“…This supports the idea of milk proteins acting as antioxidants as reported elsewhere [6,31], and the mechanism behind it may be scavenging of free lipid radicals. Alternatively the higher content of dityrosine in the cheese with high fat content could reflect more fat-soluble photo-sensitisers as found by Wold et al [32]. The fat-soluble photosensitisers detected in various dairy products [33,35], e.g.…”

“…The accumulation of lipid hydroperoxides continued even after the riboflavin had degraded, and it is proposed that the oxidation process is a chain reaction or an alternative reason could be that other sensitisers e.g. chlorophylls [35] with longer lifetime [32] were involved in the generation of lipid hydroperoxides. Lipid hydroperoxide generation did not show any dependence on the observed plateau in the generation of dityrosine or the complete loss of riboflavin.…”

“…Illumination with white light gave rise to riboflavin-mediated photooxidation [2], while porphyrins and chlorins played a more important role when exposed to red, orange and yellow light [34]. In the violet, blue and green region riboflavin, porphyrins and chlorins may play a role [32]. Riboflavin-mediated photooxidation is believed to take place through two different mechanisms.…”

Tea classification and quality assessment using laser-induced fluorescence and chemometric evaluation

“…The laser-induced fluorescence (LIF) technology has been developed for almost half a century and is now widely used in, e.g., food chemistry [15], medical diagnosis [16][17][18], microscopy [19], and remote sensing [20][21][22], especially in plant investigation. By illuminating the leaves of the plant, the LIF techniques were also used to classify the plant types and species [23], study the plant constituents [24], and investigate nutrient deficiencies in corn [25].…”

Approximate non-destructive quantification of porphyrins in butter by front face fluorescence spectroscopy

“…Presently, we assume that there are at least six different light sensitizers present in dairy products: riboflavin, protoporphyrin, haematoporphyrin, a chlorophyll a-like derivative, and two unidentified tetrapyrroles, probably porphyrins (Wold et al, 2006). The origin and formation of these tetrapyrroles are yet unclear, and the concentration levels are not known.…”