effect of accelerating drying on prune quality characteristics in a solar dryer

this study evaluated the use of the solar dryer at esfahan agricultural research center for drying prunes. a factorial experiment was carried using a randomized complete block design with four replications. the four methods used to accelerate prune drying were: control group (no treatment), mechanical perforation at one week of drying, blanching, submersion in australian cold dip method. the drying rate of the prunes was measured at: beginning of drying time (time zero), after 72 h, after 144 h, after 288 h, after 336 h. weight variation, acidity percentage, humidity percentage and tss of fruit were measured at each time interval. measurement of color loss, as well as subjective evaluations of color, taste, appearance and overall acceptability of the dried prunes was carried out at the end of drying process. the dried fruit was then stored for two months and one year and were subjected to color and subjective appearance evaluations. temperature measurement of the drying chamber indicated that the maximum temperature of the inlet air was 70°c, outlet air was 60°c and in the fruit was 51°c. the control and mechanical perforation pretreatments produced similar drying rates, while the australian cold dip method pretreatment augmented it. the blanching pretreatment produced an inferior quality of fruit. the average comparison of quantitative color indices (l*, a*, b*) showed that dried fruit produced by the control and mechanical perforation were darkest, blanching produced the most redness and australian cold dip method pretreatments produced the greatest yellowness. judges preferred dried prunes subjected to australian cold dip method for their taste and general acceptability. also they gave the highest rating to the color of dried prunes subjected to mechanical perforation pretreatment and stored for two months.