Food crystallization recrystallization

Fig. 1.19.1. Idealized diagram to show generally the dependence of phase on temperature and concentration. The dissolved, hypothetical substance consists of small carbohydrates, as found in food. The figure illustrates the meaning of 7" If a temperature range between Tf and T(2 is applied, the product can above 7" recrystallize, start melting, or remain in the amorphous phase, depending on the concentration of the dissolved substance. Below 7 -and at concentrations smaller than tv, crystallization is possible.

L-Tetrahydrofolic acid is a versatile intermediate for the manufacture of various folates, e.g., L-leucovorin [19], which is used in cancer therapy, or Metafolin , which is used as a vitamin in functional food. To our knowledge optically pure L-tetrahydrofolic acid is still obtained by repeated fractional crystallization from an equimolar mixture of diastereoisomers formed by nondiastereoselective hydrogenation of folic acid. In order to increase the yield of l-tetrahydrofolic acid and to avoid recrystallization steps, we checked the utility of our ligand for the diastereoselective hydrogenation of folic acid dimethyl ester benzenesulfonate (Scheme 1.4.4). 

The rate of recrystallization by accretion is also dependent on the probability that two crystals are in the same region and can form a bridge. This is a function of how tightly packed the crystals are in the product. The coalescence frequency has been related to the average volume of the two crystals, although the surface area has also been used to refine sintering theory. However, these theories do not fit the experimental data. Our understanding of the process of accretion recrystallization in foods is still very poor. 

Ostwald ripening (recrystallization) can also occur in these systems. It is a phenomenon by which dispersed crystals smaller than a critical size decrease in size as those larger than the critical size grow, and it can be either diffusion or surface-attachment limited. The food science literature contains several examples of diffusion-limited Ostwald ripening in aqueous carbohydrate solutions (model ice creams) [88 92]. A common feature of these reports is that no increase in ice crystal size is observed below T. ... 

For lactose production the whey is evaporated to 55-65% solid content, and the concentrate is then seeded and cooled slowly to induce sugar crystallization. The raw lactose (food quality) is recrystallized to yield a raffinade (pharmaceutical-grade lactose). Lactose is used in manufacturing of drugs (tablet filler), dietetic food products, baked products, dehydrated foods, cocoa products, beverages and ice creams. 

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