Abstract
The kinetics of lactose crystal growth in concentrated whey were studied in two stages. The first took place in a bench-top crystallizer and the second in an industrial crystallizer using concentrated whey obtained by vacuum evaporation, consisting of 3 treatments: crystallization by primary nucleation, by secondary nucleation with the addition of 0.05% and with the addition of 0.1% microcrystalline lactose. The average size of the crystals remained between 60.7 mm and 63.8 mm. The percentage of crystallization was greater in the secondary nucleation process than in the primary nucleation, where crystallization stabilized first. Mathematical equations which independently related crystallization times of the concentrated whey to the concentrations of soluble solids, crystallization percentage and mass of lactose in water were established, that can be used in the industrial setting to process whey. The kinetics of lactose crystal growth was not well described by models of first or second order reactions.
Highlights
Crystallization of lactose for the pro duction of non-hygroscopic whey powder should be performed by the mechanism of spontaneous nucleation in the evaporator or finisher, accompanied by cooling in a vacuum flash cooler and crystallizers to produce tiny crystals
Where oBrixX% = concentration of soluble solids during crystallization of whey with X% of dry matter, T = time of crystallization in minutes, R2 = correlation coefficient of the fitted model, PCC = Pearson correla tion coefficient for parametric analysis of correlation between variables, and P = coeffi cient of statistical significance. It can be seen in equations 2, 3 and 4 that for the soluble solid concentrations tested that there was a negative correlation between oBrix and time during crystallization in the whey that could be described by a second degree polynomial model
This result is important for the whey concentration and crystalliza tion since measurement of soluble solids is a simple tool for industrial monitoring of crystallization as a function of time, and application of the equations can predict the time required for a desired reduction in this solids content at 25 oC
Summary
Crystallization of lactose for the pro duction of non-hygroscopic whey powder should be performed by the mechanism of spontaneous nucleation in the evaporator or finisher, accompanied by cooling in a vacuum flash cooler and crystallizers to produce tiny crystals. According to Hynd (1980), whey powder has the tendency to absorb water from ambient air, resulting in aggregation of colloidal particles of the product during storage, caused by the replacement of part of the crystalline lactose by amorphous lac tose. When obtained without previous crystallization, whey powd er is a very fine, hygroscopic powder, with a tendency for aggregation of colloidal partic les due to the presence of lactose in an amorphous or glassy state (MASTERS, 2002). If crystallization occurs in a crystalline suspension, as normally encountered in crystallization equipment, it is referred to as secondary nucleation (NÝVLT et al, 2001)
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