Optimization of the synthesis and purification of galacto-oligosaccharides

FAROUX, J.M.; M MICAELA URETA; E. EMMA TYMCZYSZYN; ANDREA GÓMEZ ZAVAGLIA

Congreso; 11th World Congress of Chemical Engineering; 2023

Galacto-oligosaccharides (GOS), are prebiotics since they are selectively consumed by bifidobacteria and lactobacilli, generating a positive impact in the health of the host. They are conformed by galactose units (2 to 10) and a terminal glucose unit and can be obtained by enzymatic transgalactosylation from supersaturated lactose solutions in the presence of enzyme β-galactosidase [1]. GOS synthesis and lactose hydrolysis occur simultaneously, for this reason, special care needs to be considered when designing the reaction and purification process conditions. The objective of the work was to define the reaction conditions that allows maximize GOS yield and stablish an effective purification process for the reaction products through ethanol precipitation. Syntheses were carried out varying the initial concentration of lactose (30 to 50 %w/v) and the temperature (40 and 50ºC). the enzyme/lactose ratio used was 50UI/g and the pH was constant at 4.5 (adjusted with 1.7 M acetic acid). For ethanol precipitation, solutions with different sugar-ethanol ratios were used, using the samples obtained at different synthesis time (3 and 8 hours), thus managing to test solutions with different degrees of lactose hydrolysis. The solutions were incubated at 37 ºC for 16 hours, and later the precipitate was collected by centrifugation (7700 rpm, 15 minutes) [2]. The composition of the samples was analyzed by HPLC (XBRIDGE AMIDE column, acetonitrile-miliQ water solution (75:25) with 0.03% triethylamine as running solvent). Maximal GOS yield was 25.0% and 20.7%, at 40 and 50 ºC, respectively. For this reason, the purification experiments were performed using the samples obtained at 40 ºC, 40 %w/v and reaction times 3 and 8 hours. The precipitation of the 3 hours sample (20.5 %w/w GOS) with absolute ethanol gave a solid recovery percentage of 29.7% and the GOS concentration increased to 40.5 %w/w, while, with medicinal ethanol, the recovery was 13.7% and the GOS concentration increased to 49.9 %w/w. In the case of the 8 hours sample (22.2 %w/w GOS), precipitation with absolute ethanol gave a solid recovery of 29.7% giving a GOS concentration of 53.5 %w/w. In turn, the precipitation with medicinal ethanol allowed a recovery of 15% and the GOS concentration was 52.7 %w/w. Precipitates enriched in the percentage of GOS were obtained by precipitation with ethanol. The syrups obtained are easily scalable and constitute valuable ingredients to be incorporated into functional food formulation.