Colour of raspberry jam as influenced by cultivar, temperature and light during storage

Attractive red colour is one of the most important quality characteristics in raspberries for the processing industry. Fruit from four cultivars grown in the Oslofjord-area (59degrees 40'N) were used in the experiments. Jam was prepared from the cultivars 'Veten'- an important cultivar for the Norwegian processing industry, and 'Malling Admiral', 'Glen Ample' and 'Glen Rosa'. The jam was stored for three months at 4 and 20 degreesC, in the dark and under fluorescent light (950 lux). The quality parameters assessed were colour reflectance at 420, 560 and 680 urn, Hunter L*, a*, b*, total monomeric anthocyanin pigments, and degradation index of pigments as well as soluble solids. The most important result was that jam was better preserved at 4 degreesC than at 20 degreesC, as evaluated by means of Principal Component Analysis (PCA), explaining 47% of the total variation. The second most important result was the differences between the samples were as a result of pigment level, the L*, a* and b*-values and the reflectance at 680 nm. Storage in light or dark surroundings did not affect the colour of the jam after three months of storage. Good correlation between pigment level and reflectance at 420 and 560 nm was found, (r = -0.80 and -0.79, respectively). The Norwegian cultivar 'Veten', had the highest amount of pigments, followed by 'Malling Admiral', 'Glen Rosa' and 'Glen Ample'.