Effect of temperature on the cell wall composition of raisins during storage under a modified atmosphere

Raisins obtained from seedless grapes ("Flame" variety) were kept under a m odified atmosphere (MA) composed of CO2 (60%) and N-2 (40%), and stored at 10 degrees C (10MA), 20 degrees C (20MA), 30 degrees C (30MA) and 40 degree s C (40MPL). An additional sample was stored under air at 20 degrees C (20A ). Colour, and changes in cell wall components were monitored during storag e. At the end of the storage period, the 40MA and 20A samples showed a sign ificant decrease (similar to 18-19%) in the yield of cell wail material (CW M), whereas less than 6% of CWM had been degraded in the 10MA sample. The d ecrease in CWM was mainly due to pectic polysaccharide degradation, althoug h for 20A and 40MA samples, hemicelluloses were also affected. Throughout s torage, 10MA, 20MA and 30MA samples exhibited similar CWM solubility; howev er, that of the 40MA sample underwent a significant decrease, from 10% to 4 .5%, probably due to the formation of new pectic chains of higher molecular weight. In contrast, the CWM solubility of sample 20A increased from 10% t o 15%, suggesting that MA may have promoted the inhibition of pectic-polysa ccharide-degrading enzymes. In general, the combined use of relatively low temperatures and a MA helped to preserve both the colour of raisins and mai ntain the levels of their CWMs at values similar to initial concentrations.