Mutarotation and solubility of lactose as affected by carrageenans

It has been reported that polysaccharides like carrageenan can change the crystallization of lactose. However, it is still unclear whether changes in lactose mutarotation, solubility, and super-solubility are involved in carra-geenans' effect on lactose crystallization. It has been established that the conversion of alpha- to beta-lactose forms (mutarotation) in an aqueous solution has a significant impact on lactose crystallization. Similarly, lactose solubility changes lead to changes in the metastable zone (MZ), a region between the solubility and super-solubility of lactose. The width of this MZ determines the temperature drop necessary to induce lactose nucleation. This work aimed to study the effect of carrageenans on lactose mutarotation and solubility. For this purpose, lactose solutions were added with iota and kappa- carrageenan at two concentrations: 50 and 100 mg L-1. Optical rotation measurements estimated the proportion of beta/alpha isomers in lactose solutions. Besides, solubility and super-solubility was determined to build the MZ. The presence of carrageenans changed both the time to reach the mutarotation balance and the proportion of beta/alpha isomers at mutarotation equilibrium. Carrageenans decreased the solubility of lactose in a range of temperatures between 10 and 60 degrees C and reduced the metastable zone width (MZW).

Automated summary

This study aimed to investigate the impact of carrageenans on lactose mutarotation and solubility, revealing that carrageenans can affect the time to reach mutarotation balance and the proportion of beta/alpha isomers at equilibrium, while reducing lactose solubility within a certain temperature range and decreasing the width of the metastable zone.