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Comparison of critical particle diameters and its effect on flowability in stevia and sucrose, International conference on science and technique based on applied and fundamental research

Sugar is an essential food powder used in great quantities in households and food industry. Lately it is often considered healthy and different substitutes were suggested, artificial ones that are considered cancerous and natural ones like Stevia. Medicinally it was defined as a cardiac stimulant and as a treatment for obesity, hypertension and heartburn, and to help lower uric acid levels and as a treatment for obesity. In industry surrounding, problems arise during conveying of sugars, especially sucrose, due to its particle size, shape, and moisture and glass transition properties. From a food safety aspect, it is important to monitor these properties throughout industrial handling of sucrose in order to stop possible microbial contamination, dusting and production process stoppage. In this research, commercially available sucrose crystals were ground and different particle size fractions were collected using conventional sieving analysis. Stevia used as a dried leaf will not cause all above mentioned problems. For bout stevia and sucrose obtained fractions were analysed as follows: median particle diameter was determined using laser diffraction particle sizing, bulk density was determined by jolting volumeter method and flow properties (cohesiveness, caking properties and changes in compaction behaviour with different conveying speeds) was determined by powder rheometer method using Powder Flow Analyser (Stable Micro Systems, UK). Fractions obtained by sieving were in particle size range from 800 µm to 50 µm. Fractions of particle sizes below 200 µm started to exhibit flow difficulties – increased cohesion index and stronger susceptibility to caking. Mathematical correlation between particle sizes, bulk densities, cohesion and caking properties was also defined using Eureqa Formulize software package (Nutonian, USA). Crystalline form of sucrose as well as ground leaves of stevia showed different behaviour at different flow speeds in comparison with pulverized fractions, and proved to be more suitable for industry purposes.

Stevia; Sucrose; particle size reduction; flow properties

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