Influence of low pH on the metabolic activity of Lactobacillus buchneri and Lactobacillus parabuchneri strains in Tilsit-type model cheese

Round-shaped and uniformly distributed eyes are important quality features for several Swiss semi-hard cheese varieties such as Tilsit. Recently, the growth of histamine-producing strains of Lactobacillus parabuchneri has been associated with cheese defects, such as crack formation and burning taste. In this paper, the influence of pH on the metabolic activity of added strains of Lactobacillus buchneri and L. parabuchneri, which possess various CO₂-producing activities, was studied in Tilsit-type model cheeses. Two different pH values were obtained by modifying the cheese-making process (curd washing and type of ripening). Lactate, free amino acids, free short-chain fatty acids and 1,2-propanediol were determined in the ripened cheeses. In the acidic cheeses (average pH = 5.40), significantly more 1,2-propanediol was produced, presumably from lactate. Lactobacillus parabuchneri FAM 21731, a histamine-producing strain, produced small amounts of 1,2-propanediol (0.2 mmol.kg⁻¹) and high amounts of histamine (3.3 mmol.kg⁻¹). Ornithine was produced by all the studied strains, with the highest amount of 9.0 mmol.kg⁻¹ produced by L. parabuchneri FAM 21835 in the acidic cheeses. Standard cheese making representing the high pH group (curd washed and smear ripened, average pH = 5.70), and the addition of a glutamate decarboxylase-positive L. buchneri, resulted in higher amounts of γ-aminobutyric acid (GABA) (8.1 compared to 3.3 mmol.kg⁻¹ in the control standard cheeses). Irrespective of the strain, the GABA level was much higher in all the acidic cheeses than in the standard cheeses (14.7 compared to 4.6 mmol.kg⁻¹, respectively). The study clearly demonstrates the importance of the cheese pH in the metabolic activity of the added strains during cheese ripening.