No more cleaning up - Efficient lactic acid bacteria cell catalysts as a cost-efficient alternative to purified lactase enzymes

• Published in: Applied microbiology and biotechnology Vol. 104; no. 14; pp. 6315 - 6323
• Main Authors: Wang, Qi, Lillevang, Søren Kristian, Rydtoft, Signe Munk, Xiao, Hang, Fan, Ming-Tao, Solem, Christian, Liu, Jian-Ming, Jensen, Peter Ruhdal
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.07.2020; Springer; Springer Nature B.V
• Subjects: Animals; Antimicrobial peptides; Applied Microbial and Cell Physiology; Bacteria; Biological products; Biomedical and Life Sciences; Biotechnology; Catalysts; Cell culture; Cell Membrane Permeability - drug effects; Cleaning; Culture Media; Dairy products; Dairy wastes; Enzymes; Hydrolysis; Lactase; Lactase - metabolism; Lactic acid; Lactic acid bacteria; Lactobacillales - growth & development; Lactobacillales - metabolism; Lactobacillus; Lactococcus lactis; Lactococcus lactis - growth & development; Lactococcus lactis - metabolism; Lactose; Lactose - analysis; Lactose - metabolism; Life Sciences; Low cost; Microbial Genetics and Genomics; Microbiology; Microorganisms; Milk; Milk - chemistry; Milk - microbiology; Nisin; Nisin - metabolism; Nisin - pharmacology; Physiological aspects; Streptococcus thermophilus; Streptococcus thermophilus - drug effects; Streptococcus thermophilus - growth & development; Streptococcus thermophilus - metabolism; Temperature; Thermophilic microorganisms; China; Nisin; Permeabilization; Lactase; Lactose-free; Streptococcus thermophilus
• ISSN: 0175-7598; 1432-0614
• DOI: 10.1007/s00253-020-10655-3

β-galactosidases, commonly referred to as lactases, are used for producing lactose-free dairy products. Lactases are usually purified from microbial sources, which is a costly process. Here, we explored the potential that lies in using whole cells of a food-grade dairy lactic acid bacterium, Streptococcus thermophilus , as a substitute for purified lactase. We found that S. thermophilus cells, when treated with the antimicrobial peptide nisin, were able to hydrolyze lactose efficiently. The rate of hydrolysis increased with temperature; however, above 50 °C, stability was compromised. Different S. thermophilus strains were tested, and the best candidate was able to hydrolyze 80% of the lactose in a 50 g/L solution in 4 h at 50 °C, using only 0.1 g/L cells (dry weight basis). We demonstrated that it was possible to grow the cell catalyst on dairy waste, and furthermore, that a cell-free supernatant of a culture of a nisin-producing Lactococcus lactis strain could be used instead of purified nisin, which reduced cost of use significantly. Finally, we tested the cell catalysts in milk, where lactose also was efficiently hydrolyzed. The method presented is natural and low-cost, and allows for production of clean-label and lactose-free dairy products without using commercial enzymes from recombinant microorganisms. Key points • Nisin-permeabilized Streptococcus thermophilus cells can hydrolyze lactose efficiently. • A low-cost and more sustainable alternative to purified lactase enzymes. • Reduction of overall sugar content. • Clean-label production of lactose-free dairy products.