Mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake
1995
Lazarides, H.N. | Katsanidis, E. | Nickolaidis, A.
A model fruit (apple) was used to study mass transfer kinetics during osmotic preconcentration aiming at minimal solid uptake. The effects of process temperature, osmotic solution concentration and 'molecular size' of osmotic solute on water loss (WL) and solid gain (SG) were evaluated. Temperature and concentration effects were evaluated with 45-65% (by weight) sucrose solutions at 20-50 degrees C. The effect of solute size was monitored using corn syrup solids with different degrees of polymerisation (dextrose equivalent (DE) levels between 18 and 42). increased temperatures gave increased WL and SG rates, favouring faster water loss (higher WL/SG ratios). Increased concentrations also resulted in higher WL and SG rates; yet, they favoured faster solid uptakes (lower WL/SG ratios). Among all sucrose treatments, preconcentration in 55% sucrose solution at 50 degrees C gave the highest WL/SG ratio. Overall mass (solids) transfer coefficient decreased with the size of osmotic solute. Corn syrup solids of larger 'molecular size' (<38 DE) gave negative net solid gain values, indicating a sugar uptake marginally inferior to leaching of fruit solids; the 42 DE corn solids gave by far the highest WL/SG ratio among all experimental treatments.
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