Xylitol crystallization from culture media fermented by yeasts

Among sugar substitutes, an important role is played by xylitol, an aliphatic pentitol provided with some interesting properties which make it a high value product for pharmaceutical, odontological and food industries. Its production by biotechnological methods is based on fermentation of agro-industrial residues and could potentially compete with the traditional chemical way. However, crystallization is an important stage of xylitol production, since in many respects it determines the yield and quality of the target product. In the present work tests were made in order to determine the best conditions to clarify fermented media, which were then subjected to isothermal crystallization in the presence or in the absence of residual xylose and varying xylitol concentration as well as cooling temperature (?10 ≤ T_c ≤ 15 °C). Besides, the kinetics of xylitol crystallization from fermented solutions was investigated as function of the initial solution supersaturation and cooling temperature. The effect of the presence of residual xylose on the rate of crystallization was also evaluated. The best clarifying treatment was found to be 20 g l^?1 activated charcoal at room temperature for 1 h. The study of xylitol crystallization revealed the positive effect of the presence of residual xylose, which ensured a 1.6-fold increase in the crystallization yield (from 0.27 to 0.42).