English abstract
Date fruit syrup is characterized by high content of sugars. There are different ways in which date fruit syrup could be produced, such as traditional and the industrial methods. These methods of production could lead to produce different physico-chemical properties. Moreover, date fruit syrup is subjected to crystallization and could be considered as a quality defect if not controlled. Thus, the objectives of this study were to analyze the physico-chemical properties of date fruit syrup produced by the traditional and industrial methods. Total ten samples of date fruit syrup were purchased from different regions in Oman, three of them were industrial syrup and seven were traditional syrups. The physico-chemical characteristics and rheology of samples were analyzed and then classified based on cluster analysis from Principle Component Analysis (PCA). The results of the physico-chemical characteristics showed that the syrups could be classified into two groups or cluster. Crystallized syrup was produced naturally and in controlled conditions (seeded syrup) which is called set syrup and stored at different temperatures (25 °C to -20 °C). The crystallized syrups were analyzed by differential scanning calorimtery (DSC), X-ray diffraction (XRD) and polarized light microscopy. The set syrup crystals showed uniform formation of crystals with time compared to the naturally crystallized syrup. The XRD data showed three main characteristic peaks at different storage temperatures, and some of those peaks were matching with glucose monohydrate. The polarized light microscopy images showed that crystals size was decreased with the decrease of temperature. State diagram of crystalized syrup was developed by measuring freezing curve, glass transition, crystalsmelting and maximal-freeze-concentration condition by measuring the thermal characteristics of the samples with different moisture contents. The ultimate maximalfreeze-concentration condition of set syrup was determined as -42.8 °C and the unfreezable water was as 0.27 g/g sample. The eutectic temperature and solids content at eutectic point were as -10.2 °C and 0.39 g/g sample, respectively.
