| Summary: | Shell-on-prawns (SOP) are a delicacy product of the cold-water prawn Pandalus borealis . SOP are commonly stored at the retail in an illuminated display freezer for an extended period of time. Previous studies have shown that illuminated frozen storage causes rapid oxidation in SOP, which is expressed as a change in colour from a light, pinkish to a more pale, orange and finally yellow colour, together with odour and taste changes. Little is known about the underlying mechanisms of the changes occurring. The present study aimed to understand how and when the oxidation occurs in the presence and absence of light. A second aim was to identify relevant storage conditions and time for subsequent experiments with antioxidant addition to SOP. SOP (average oil content 3.32±0.32%) were packed in air and stored at -20.6±1.21°C with and without light for 84 days. Samples were taken every 14 days, followed by an investigation of oxidative stability (PV, secondary oxidation products, and α-tocopherol consumption). Results showed an increase in PV from the initial 3.39±0.48 meq/kg O 2 /kg oil to 22.09±1.45 meq/kg O 2 /kg oil with light and 7.8±2.25 meq O 2 /kg oil without light. A difference between treatments was observed after 70 days of storage. No consumption of α-tocopherol was observed during the storage period. Colour measurements (CIELab) showed an increased L* value, and decreases of the a* and b* values. The colour changes could not be explained by pigment change, as the astaxanthin content was not affected by the storage. In line with the PV results, differences were observed in the concentrations of secondary oxidation products (2,3-pentadione, heptanal, 2-methyl-butanal, 3-methyl-butanal) between samples stored with and without light. It was noticeable that changes were not observed until after four weeks of storage. The chosen storage conditions were sufficient to show the effect of illuminated storage on SOP products.
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