Inside out–a sustainable strategy harnessing smear bacteria for accelerating cheese ripening

• Direct addition of Brevibacterium linens MA5 accelerates cheese ripening from inside-out. • Avoiding protease-positive lactococci helps reduce formation of bitter peptides in cheese. • Bicarbonate brining boosts smear growth and removes the need for surface smearing. • The strategy enables more sustainable and efficient industrial cheese production. Bacterial smear-ripening of cheeses usually takes at least one month because of the slow growth of the bacteria on the rind. To bypass this bottleneck in ripening, we have devised a novel strategy for smear ripening that involves adding milk cultures of specific smear bacteria directly to the cheese milk, which not only obviates the need for smearing the cheeses but also adds a source of peptides and free amino acids that promote the growth of the primary starter and accelerate the overall ripening process. As the candidate smear bacterium, we chose Brevibacterium linens MA5 (MA5), which was isolated from a Danish Danbo cheese undergoing smear ripening. Strain MA5 was selected due to its superior proteolytic capacity, tolerance to low pH, and relatively fast growth as compared to commercially available B. linens strains. Among the smear isolates, MA5 was also superior in terms of releasing peptides and amino acids from milk protein, which could promote the growth of the protease-negative Lactococcus lactis strain EC2 (EC2). Vacuum-packed cheeses prepared from milk supplemented with 10% (v/v) of an MA5 milk culture accumulated free amino acids more rapidly during ripening. When these cheeses were exposed to air after being soaked in a 10% sodium bicarbonate solution to elevate the pH of the rind, rapid growth of MA5 on the rind was observed, establishing a dense smear within a week. Overall, this novel approach offers a sustainable and resource-efficient method for accelerating the ripening of smear-ripened cheeses, while eliminating the need for proteolytic lactococci that contribute to bitterness.