اثر روش خشك كردن بر برخي از خواص كيفي و ترموفيزيكي خرماي رقم استعمران و پودر حاصل از آن

چكيده انگليسي :

Effect of Drying Method on Some Qualitative and Thermo Physical Properties of Istamaran Date Variety and its Powder Esmaeil Arar Gatea Email address esmaeil arar@gmail com January 31 2012 Department of Farm Machinery College of Agriculture Isfahan University of Technology Isfahan 84156 83111 IranDegree M Sc Language FarsiSupervisors Morteza Sadeghi sadeghimor@cc iut ac ir Seyed Jalil Razavi jrazavi@cc iut ac ir Abstract Date Pheonix dactylifera L is one of the most important horticultural crops and foreign exchangeearning sources of Iran Annual products of date in Iran has been nearly 50 million tons since 50 yearsago while 30 of this amount as losses is consumed for animal feeding Date powder as one of the by products is achieved by drying and milling dates waste and is used in making pastry ice cream etc Oneof the problems encountered by fruits powder producing industry is stickiness during drying processingand storage The stickiness of fruits powder is generally caused by the low molecular weight of sugarsincluding fructose glucose sucrose as well as some organic acids in fruits Date fruit contains thesesugars as well To control the stickiness in food processing the amount of water content in foods andphysical state of solid contents must be realized Moisture sorption isotherms are important to determinechanges in moisture content during storage of food materials thermodynamic conditions of mixingproducts and decisions regarding the use of undesirable chemical and enzymes reactions On the otherhand determination of the glass transition temperature Tg is the matter of importance as a powerful toolfor understanding water properties in the food and control of products shelf life The parameters of thefinal product in the drying process such as water activity porosity physicochemical structure and colorare dependent on drying methods The objectives of the present study were to determine and modelingmoisture sorption isotherms of the dried date powder obtained by various drying methods study ofmoisture sorption kinetics of date powder and effect of drying method on qualitative characteristics ofdried date and its powder as well as performing thermal analysis on date powder of waste Istamaran datevariety The drying methods used in this study were hot air microwave and vacuum drying Moisturesorption isotherms were determined at seven levels of water activity and three temperatures of 25 35 and45 C The appropriate model among nine well known models was selected based on the highestcorrelation coefficient and the smallest root mean square error and the minimum mean relative deviationmodulus The qualitative parameters included water absorption capacity WAC dry matter holdingcapacity DHC rehydration ability RA and shrinkage for dried date as well as color indices L a and b for dried date and its powder The glass transition temperature of date powder samples was measured bydifferential scanning calorimetry DSC method Thermal analysis was performed at 90 to 100 C at 10 C min 1 Six semi empirical and theoretical models were used to model the glass transition temperatureof the date powder According to the results the GAB model was found to be the most accurate model forpredicting the equilibrium moisture content EMC of date powder for all treatments The effect of dryingmethod on WAC DHC and RA was significant but its effect on the shrinkage of dried date was notsignificant Also its effect on color indices was significant Microwave dried samples had a darker colormost likely due to caramelization during drying Thermal analysis revealed that by increasing the watercontent from 0 013 to 0 178 Tg decreased from 21 75 to 49 15 C Tg value of the samples was predictedusing various model systems and Gordon Taylor and Coachman Karasz models based on the componentsof the considered model systems The results showed that none of the model systems had a goodprediction for the glass transition temperature of date powder The results indicate that the da

عرارگاطع، اسماعيل

اثر روش خشك كردن بر برخي از خواص كيفي و ترموفيزيكي خرماي رقم استعمران و پودر حاصل از آن

دماي گذار شيشه اي , ظرفيت گرمايي , مدل سازي , همدماي جذب رطوبت