Unveiling the hidden potential of nisin-permeabilized Streptococcus thermophilus as proteolysis accelerant during cheese ripening

Proteolysis is the most significant primary ripening process in cheese, as it produces amino acids that serve as precursors for various flavor compounds. Therefore, the degree of proteolysis is an important indicator of cheese ripening. Here, the potential of nisin-permeabilized lactic acid bacteria as proteolysis accelerant during cheese ripening was explored. Both nisin-permeabilized Lactococcus lactis and Streptococcus thermophilus cells could hydrolyze peptidase substrates lysyl-p-nitroanilide (Lys-pNA) and glycyl-pro-pNA [Gly-Pro-pNA] efficiently. The overall proteolytic capacity of permeabilized cells depended on nisin concentration, strain used, temperature, and pH. The best candidate, S. thermophilus ST057-1, could hydrolyze 80% Lys-pNA and 94% Gly-Pro-pNA at 30 C and pH 7 when treated with 5 mu g/mL nisin. Permeabilized ST057-1 cells, when used as a starter adjunct, led to a significant increase in free amino acid content in model cheeses, up to 1.5 times that of the reference cheese, within 80 days of cheese ripening. This study highlights the potential of utilizing nisin-permeabilized S. thermophilus cells as an adjunct to accelerate proteolysis during cheese ripening.