Abstract
The sorption behaviour and water transport mechanisms inside Spirulina platensis samples were experimentally analysed during isothermal drying at 25℃ and 50℃. Two different products grown in semi-industrial farms from Burkina Faso and France with initial water contents respectively of the range from 2.73 kg w /kg dm to 3.12 kg w /kg dm were characterized. A novel procedure has been developed to determine the water content profiles inside samples during isothermal drying. At both temperatures, experimental results underlined that the physical properties of Spirulina are not sensitive to the geographical origin, Burkina-Faso or France. To keep Spirulina at an water activity below 0.6 in order to preserve it from micro-organisms development, sorption isotherm curves show that a sufficient requirement is to lower the water content until an upper limit of w = 0.075 db. The evolution of water transport coefficient as a function of water content highlights a monotonous exponential dependence with a transport coefficient ranging from 1.70 × 10–10 to 94 × 10–10 m2/s. The contribution of solid phase shrinkage to the transport of water is negligible for the last drying steps.
Highlights
Microscopic observation shows that Spirulina platensis is in spiral form with much tighter turns than those of other kind [24]
We find that for water contents of the order of w = 3, the values obtained by the Crank method [12] with a velocity of the imposed air are lower than those given by cutting approach
Theses profiles are introduced in a theoretical modelling accounting for matrix shrinkage and relative water flux leading to identifying the dependence of water transport coefficient with respect to water content
Summary
Their production mode is no different from one farm to another, from one country to another. Microscopic observation shows that Spirulina platensis is in spiral form with much tighter turns than those of other kind [24]. In both farms, harvested Spirulina is drained and rinsed through a 20 μm filter. Parameters Solid apparent density Water apparent density
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