Preservation factors and processing effects on anthocyanin pigments in plums

The use of a combination of preservation factors has been suggested as a viable alternative to minimally process fruits and preserve them for practical periods of time. Although microbiological stability is the main goal, in the case of prunes color preservation is also of great concern. Prunes (Prunus domestica L.) of the ‘Angeleno’ variety were employed. The fruits were cut in half and the seeds removed. A treatment of 150 s under steam resulted in the permanent inactivation of browning enzymes. The treated fruit was stored for 90 days in systems (aw = 0.98 with sucrose and 0.1 % benzoate) at three different pH values: 2.95, 3.45 and 3.95. After 90 days of storage at room temperature, 77% of the original anthocyanin remained at pH 2.95, but only 29% at pH 3.45 and 8% at pH 3.95. There was also an increase in the degradation index with time and with increasing storage pH. Color density values decreased as a result of anthocyanin degradation and not because of browning reactions. A marmalade prepared using the pH 2.95 preserved prunes was stored at room temperature for 90 days. An additional 27% of the original anthocyanin was destroyed, but the degradation index increased only slightly and remained constant throughout the storage period. Color density values remained very low. No microbial growth occurred in the stored prunes or marmalade, and the marmalade was classified organoleptically as good.