A Three-Step Process for the Bioconversion of Whey Permeate into a Glucose-Free D-Tagatose Syrup

Fadia V Cervantes,Francisco J Plou,Zoran Merdzo,Sawssan Neifar,Antonio O Ballesteros,Lucia Fernandez-Arrojo,Samir Bejar,Maria Fernandez-Lobato,Javier Viña-Gonzalez

doi:10.3390/catal10060647

Abstract

We have developed a sustainable three-stage process for the revaluation of cheese whey permeate into D-tagatose, a rare sugar with functional properties used as sweetener. The experimental conditions (pH, temperature, cofactors, etc.) for each step were independently optimized. In the first step, concentrated whey containing 180–200 g/L of lactose was fully hydrolyzed by β-galactosidase from Bifidobacterium bifidum (Saphera®) in 3 h at 45 °C. Secondly, glucose was selectively removed by treatment with Pichia pastoris cells for 3 h at 30 °C. The best results were obtained with 350 mg of cells (previously grown for 16 h) per mL of solution. Finally, L-arabinose isomerase US100 from Bacillus stearothermophilus was employed to isomerize D-galactose into D-tagatose at pH 7.5 and 65 °C, in presence of 0.5 mM MnSO4. After 7 h, the concentration of D-tagatose was approximately 30 g/L (33.3% yield, referred to the initial D-galactose present in whey). The proposed integrated process takes place under mild conditions (neutral pH, moderate temperatures) in a short time (13 h), yielding a glucose-free syrup containing D-tagatose and galactose in a ratio 1:2 (w/w).

Highlights

D-Tagatose is one of the most promising low-calorie functional sweeteners [1]
Chemical Composition of Whey Permeate. It is well reported the effect of metal ions on the activity and stability of many enzymes, including those involved in the transformation of carbohydrates, and in particular in the two enzymes involved in the present work: β-galactosidase [40] and L-arabinose isomerase [41]
Since a temperature of 65 ◦ C was selected for the isomerization reaction, and considering that the conversion from D-galactose to D-tagatose was higher in presence of MnSO4 in the reaction medium, we decided to maintain

Summary

Introduction

D-Tagatose is one of the most promising low-calorie functional sweeteners [1]. It is a ketohexose, namely a C4 epimer of D-fructose. Very stable at pH values between 2.0 to 7.0, and highly soluble in water (58% w/w at room temperature). It possesses a sucrose-like taste with 92% of its sweetness but contributing only 1.5 kcal/g (38% compared to sucrose) [3], with no cooling effect or aftertaste [4]. D-Tagatose was approved as a novel food in the European Union [3] and has obtained

Methods

Results

Conclusion