Effects of κ-Carrageenan on Crystallization and Invertase Activity in Lactose-Sucrose Systems

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 carrageenans' effect on lactose crystallization. It has been established that the conversion of α- to β-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 ι and κ- carrageenan at two concentrations: 50 and 100 mg L^-1. Optical rotation measurements estimated the proportion of β/α 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 β/α isomers at mutarotation equilibrium. Carrageenans decreased the solubility of lactose in a range of temperatures between 10 and 60 °C and reduced the metastable zone width (MZW).

Ultrasound-assisted crystallization of lactose in the presence of whey proteins and κ-carrageenan

The conventional process of lactose crystallization is prolonged, hardly controllable and the crystals have low quality. In this work, the effect of ultrasound on the crystallization of lactose in an aqueous system was assessed. Additionally, it was studied how the presence of whey proteins (which are a common impurity) and κ-carrageenan (that possess high water-binding capacity) could modify the process of lactose crystallization. Lactose solutions at 25% were sonicated in a continuous flow chamber at two different energy densities (9 and 50 J mL^-1) before the start of crystallization. Some of these lactose solutions were previously added with κ-carrageenan (0, 150 and 300 mg L^-1), with whey proteins (0.64%) or with both at the same time. Ultrasound sped up the rate of crystallization, decreased the crystal's size and narrowed the crystal size distribution (CSD). The presence of whey proteins accelerated the process of crystallization but induced the formation of amorphous lactose. Likewise, the rate of lactose crystallization was improved by the addition of 150 mg L^-1 of carrageenan. Whereas, the combination of carrageenan and whey proteins generated the smallest crystals (6 μm), the narrowest CSD and minimized the formation of amorphous lactose.