Screening and selection of Lactobacillus strains for use as adjunct cultures in production of semi-hard cheese.

Thirty-three Lactobacillus strains were tested as adjuncts in a cheese model system. Eighteen strains originated from cheese (nine Lactobacillus spp. and nine Lb. paracasei/casei) and 15 from human intestinal mucosa (11 Lb. rhamnosus; three Lb. paracasei; one Lb. plantarum). Model cheeses weighing 120 g were made of cheese grains from full-scale production of washed curd semi-hard cheese (Herrgård). The model system was reproducible and similar to full-scale production with respect to moisture, salt content, pH and microbial flora. The model cheeses were sampled for aerobic and anaerobic plate count and viable counts of Lactobacillus and Lactococcus. The presence of adjuncts in the model cheeses was confirmed by typing isolates with Randomly Amplified Polymorphic DNA (RAPD). The sensory properties of model cheeses were described. In a first trial 23 of the 33 adjuncts were re-isolated from the corresponding model cheeses after 9 or 13 weeks. Adjuncts of Lb. paracasei were re-isolated more frequently than adjuncts of Lb. rhamnosus. Nine strains were selected, on the basis of their ability to grow and be a dominating part of the microflora of model cheese with interesting sensory properties. These strains were further studied together with two commercial cultures. The sensory influences on model cheeses of six of the adjuncts were confirmed, and flavour scores were in the range of 2.9-7.1 for model cheeses with different adjuncts while the control had a flavour score of 5.6 (0-10 scale). Survival and growth of seven out of the nine strains correlated with the results of the first trial. Growth and influence on flavour of four adjunct cultures were confirmed in experimental cheese manufactured in a 400-1 open vat.