Trienzymatic Complex System for Isomerization of Agar-Derived d‑Galactose into d‑Tagatose as a Low-Calorie Sweetener

• Published in: Journal of agricultural and food chemistry Vol. 68; no. 10; pp. 3195 - 3202
• Main Authors: Jeong, Da Woon, Hyeon, Jeong Eun, Shin, Sang Kyu, Han, Sung Ok
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 11.03.2020
• Subjects: Aldose-Ketose Isomerases - chemistry; Bacterial Proteins - chemistry; Biocatalysis; Flavobacteriaceae - enzymology; Galactose - chemistry; Galactosidases - chemistry; Glycoside Hydrolases - chemistry; Hexoses - chemistry; Isomerism; Lactobacillus sakei - enzymology; Sweetening Agents - chemistry; l-arabinose isomerase; d-tagatose; red algae; agarolytic complex
• ISSN: 0021-8561; 1520-5118
• DOI: 10.1021/acs.jafc.9b07536

d-Tagatose is a rare monosaccharide that is used in products in the food industry as a low-calorie sweetener. To facilitate biological conversion of d-tagatose, the agarolytic enzyme complexes based on the principle of the cellulosome structure were constructed through dockerin–cohesin interaction with the scaffoldin. The construction of agarolytic complexes composed of l-arabinose isomerase caused efficient isomerization activity on the agar-derived sugars. In a trienzymatic complex, the chimeric β-agarase (cAgaB) and anhydro-galactosidase (cAhgA) from Zobellia galactanivorans could synergistically hydrolyze natural agar substrates and l-arabinose isomerase (LsAraA Doc) from Lactobacillus sakei 23K could convert d-galactose into d-tagatose. The trienzymatic complex increased the concentration of d-tagatose from the agar substrate to 4.2 g/L. Compared with the monomeric enzyme, the multimeric enzyme showed a 1.4-fold increase in tagatose production, good thermostability, and reusability. A residual activity of 75% remained, and 52% of conversion was noted after five recycles. These results indicated that the dockerin-fused chimeric enzymes on the scaffoldin successfully isomerized d-galactose into d-tagatose with synergistic activity. Thus, the results demonstrated the possibility of advancing efficient strategies for utilizing red algae as a biomass source to produce d-tagatose in the industrial food field that uses marine biomass as the feedstock.