Production of Prebiotic Galacto-Oligosaccharides from Acid Whey Catalyzed by a Novel β-Galactosidase from Thermothielavioides terrestris and Commercial Lactases: A Comparative Study

Abstract

The steadily increasing global popularity of Greek strained yoghurt has necessitated alternative valorization approaches for acid whey, the major straining process effluent. In this context, prebiotic galacto-oligosaccharides can be enzymatically synthesized from acid whey lactose, via either commercial or novel β-galactosidases. A comparative study of galacto-oligosaccharide production from acid whey was carried out, employing two commercial β-galactosidases (from Kluyveromyces lactis and Aspergillus oryzae) and one novel, in-house produced (from Thermothielavioides terrestris), as a function of the initial lactose content and enzyme load. Selected reaction conditions for β-galactosidases from K. lactis, A. oryzae, and T. terrestris were 35 °C at pH 7.2, 45 °C at pH 4.5, and 50 °C at pH 4.0, respectively. Maximum galacto-oligosaccharide yields equal to 23.7, 23.4, and 25.7% were achieved with, respectively, 0.13 U/mL of K. lactis β-galactosidase in non-concentrated acid whey, 4 U/mL of A. oryzae β-galactosidase, and 8 U/mL of T. terrestris β-galactosidase in acid whey concentrated to 20% w/v initial lactose content. The increased galacto-oligosaccharide productivity of the thermophilic β-galactosidase from T. terrestris can be a determining asset in a combined concentration and oligomerization industrial process. This will allow for high galacto-oligosaccharide yields for efficient, cost-effective production of valuable prebiotics from acid whey.

Cheese and Yogurt By-Products as Valuable Ingredients for the Production of Prebiotic Oligosaccharides

“…Thus, it is concluded that the increased concentration of these cations in AW either enhances lactose hydrolysis or inhibits transgalactosylation reaction. In our previous study [28], it was observed that Ca 2+ makes K. lactis lactase more active, while Mg 2+ acts as an inhibitor, even at low concentrations (24.31 mg/L).…”

“…The whey concentration up to 15% w/v lactose content was achieved using a Hei-VAP Value Digital Rotary Evaporator (Heidolph Instruments, Schwabach, Germany). The proximate analysis for AW was previously performed, and the corresponding results were retrieved according to Limnaios et al (2023) [28] for the purpose of a comprehensive comparative study.…”

“…Galactooligosaccharide production from SW and AW was performed via the application of two industrially applied lactases: one β-galactosidase sourced from the yeast Kluyveromyces lactis (Kerry Group plc, Tralee, Kerry, Ireland) and one derived from the fungus Aspergillus oryzae (Sigma-Aldrich, St. Louis, MO, USA). Optimum reaction temperature in terms of activity and thermostability have been determined at 35 and 45 • C for the lactase from K. lactis and A. oryzae, respectively, while corresponding optimum pH values have been determined as 4.5 and 7.2, respectively, according to our previous study [28].…”

“…Enzymatic reactions conducted in order to produce GOSs from SW and AW took place in both non-concentrated SW and AW with initial lactose contents (c lac(0) ) of 5.1 and 3.1% w/v, respectively, as well as in SW and AW concentrates with c lac(0) values of 10% and 15% w/v, respectively. Each reaction was carried out in duplicate at the optimal reaction conditions of each lactase, as mentioned in Section 2.2, and the process is described in Limnaios et al (2023) [28].…”

“…Further separation of the produced GOSs according to their degree of polymerization at the optimum reaction conditions in each case was achieved through high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD), thus following the methodology described in Limnaios et al (2023) [28]. All analyses were performed in duplicate.…”