Abstract
•Khalas date fruits dried more than Ruzeiz ones.•Diffusion was mechanism governing moisture movement in date fruits.•Page model was more accurate in predicting the measured drying curve data.•Date fruits mass and pH properties were affected by solar drying.•Date fruits length, width and colour properties were not affected by solar drying.
Determination of the drying curves characteristics of date fruits at tamar (fully ripe) stage of Khalas and Ruzeiz varieties by using two constructed solar dryers namely; direct solar dryer (DSD) and indirect solar dryer (ISD), Modelling of drying curves data of date fruits for both varieties and solar dryers, and the effect of solar drying process on four physico-chemical properties of the date fruits for both varieties and solar dryers were investigated. The four physico-chemical properties included linear dimensions of length and width, mass, colour L, a, and b values and pH. The two solar dryers were constructed from local materials and were used in the date fruits drying. Study experiments were carried out at The Research and Training Station of King Faisal University, Al-Ahsa, KSA. Results for both varieties and solar dryers showed that Khalas date fruits dried more than Ruzeiz ones and date fruits drying took place predominantly in the falling rate period i.e. diffusion was the main physical mechanism governing moisture movement in date fruits. Page model was more accurate in predicting the measured drying curve data. Generally, under the present study solar drying conditions, some physico-chemical properties of mass and pH of date fruits were affected, while properties of linear dimensions (length and width) and colour L, a, and b values were not. This concluded that under similar drying conditions of the study some unit operations of date fruits processing such packaging, sorting and grading they will not be affected.