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Abstract The pre4drying treatments included the application of SOme blanching and soaking treatments for the purpose of comparing their efficiency in stopping or decreasing colour change in the peeled sliced fruits until the completion of steps leading to their dehydration. The effect of soaking or blanching treatment was investigated before and after dehydration9 With all soaking and/or blanching treatments, the dehydration conditions orveemna)i.ned constant (drying at 600C for 20 hrs in air-circulated 1- A soaking solution of 0.4% NaZS~05 at room temperatureapplied for 10 and 15 min for peeled s11ced apple and pears, res~ pective1y, induced the best colour in dehydrated materials. 2- Organoleptic evaluation of sun-dried prOducts indicated that they did not show satisfactory Scores Overall organoleptic evaluation for 32 dehydration trials with apple and 18 trials with pears was performed with the aid o~ trained judges. Organoleptic scores as well as the visual estimation of these dehydrated products indicated that Anna apple variety was more acceptable than Baladi apple and that artificial dehydrated apples were superior to sun~dried ones. A dipping solution of 0.4% NaZSZOS indaupcpelde thaendhpiegahress.t organoleptic SCores with both dehydrated 4- All blanching treatments did not show satisfactory results from the standpoint of colour of dehydrated-blanched fruit pieces. Although some solutes were found effective in maintaining or enhancing the colour when used as in_ gredients for preliminary dipping treatments at room temperature?they did not show any significant influence upon their use as solutes for blanching treatmen~ possibly because of the high temperature of blanching. 5- Dehydrated frUits previously blanched at BOoc were found comparable with their Control samples from the standpoint of colour, upon using the tested blanching solutions. After applying the designated soaking treatments (9 treatments), visual estimation of the soaked peeled frUit pieces revealed that Using solution of 1% citric acid +0.5% NaCl for 5 min of dipping gave the best result from the standpoint of stability of colour. However, increasing dipping period more than 10 min showed some degree of colour changes. With both apple and pears, increasing soaking only 3 min using 1% citric acid and OoS% NaCl improved colour of dehydrated fruit material their corresponding control treatments. 7- Solutions of N~2SZ0S alone were found more effective tiffin NaZSZOS combined with CaClz solution in producing better colour for dehydrated material, with all soaking period tested. period to solution compared to 8- Four degrees of dehydration temperature (50, 60, 70, and SOoC) were compared together with the application of three different drying intervals (10, 15 and ZO hrs.)~while the soaking pretreatment was constant (0.4% NaZSZOS for 10 min with apple and 15 min with pears1were effectivated. Increasing temperature of dehydration than 700C influenced colour of both dehydrated fruits with all the drying periodstested, except in case of using SOOC for 10 hrs 0 Increasing period of dehydration influenced colour on16 upon using higher dehydration temperature of 75 and 80 C. In view of the comparable results obtained for various dehydration trials tested, from the standpoint of appearance , organoleptic properties and induced colour changes in dehydrated materials, it was decided to continue research on the effect of some selected optimum conditions on some aspects of physical dehydration and properties as well as chemical composition of the obtained dehydrated materials directly after processing and after certain periods of storage. All treatments which induced higher organoleptic scores than 82 were selected (13 treatments) which included those employed 0.4% Na2SZ0S as dipping solution before dehydration followed by artificial drying at temperatures of 500, 70°, SOoC for 10 hrs; 70°C for IS hrs, in case of both fruits, and those dehydrated at Soo, 60° and 700C for 20 hrs in case of apples and 50 and 60°C for 20 hrs in case of pears. 9- Drying ratio of freshly dehydrated samples ranged between 1: 6.2 to 1:6.5 in case of apples and between 1: 5.3 to 1:5.5 in case of pears. 10- The increase in degrees of temperature and in period of dehydration druing processing resulted in lower moisture content with all dehydrated products which ranged between 14.98 to 11.45 in case of apples and between 12.908 to 9.989 in case of pears. 11- The increase in aefrees of teaperature and in period of dehydration dur~1 processing influenced the rehydration properties. where the higher the extent of these factors the lower the redehydration values. Rehydration ratioes, coefficient of rehydration and moisture content (%) in rehydrated samples ranged between 1:200 to 1:3.0 ; 0.31 to 0.48 and 55.5 to 71.7%, respectively, after soaking dehydrated apples in water for 1 hrj on the other hand, they ranged between 1: 1.9 to 1: 2.9 ; 0.35 to 0.55 and 52.6 to 70%, respectively, after 1 hr of soaking dehydrated pears. 12- With both apples and pears, moisture formed the highest percentage in the chemical composition of fresh peeled flesh and peels while crude fiber formed the second major constituent and crude protein represented the third principal constituent. |