From “Viili” Towards “Termoviili”, a Novel Type of Fermented Milk: Characterization of Growth Conditions and Factors for a Co-culture of Lactobacillus delbrueckii and Geotrichum candidum

The traditional Northern fermented milk product “Viili” is based on the use of a starter comprising both mesophilic lactic acid bacteria (LAB) and Geotricum candidum mold strains for milk fermentation at 18 to 20°C for about 20 hours. The goal of the present study was to investigate whether there is a microbiological basis for the conception of a novel type of fermented milk product “Termoviili”, which would be a hybrid between “Viili” and yogurt, because of the use of thermophilic Lactobacillus delbrueckii instead of mesophilic LAB as a starter component. Accordingly some critical growing conditions and factors that support a co-culture of Lb. delbrueckii ssp. lactis ATCC 15808 and G. candidum VV strains were determined and further compared to a yogurt starter like co-culture of Lb. delbrueckii ssp. lactis ATCC 15808 and Streptococcus thermophilus T101 strains. Both Lb. delbrueckii and G. candidum could grow at a temperature range of 30-34°C, and optimally at 30°C. At this temperature, the co-culture of Lb. delbrueckii and G. candidum showed similar synergistic interactions, like the yogurt starter co-culture, when growth occurred in a milk base, which had not been subjected to strong heat treatment like autoclaving at 121°C for 10 minutes. Formic acid, at a concentration of 7.35 mM, stimulated the growth of Lb. delbrueckii ssp. lactis ATCC 15808, likewise when G. candidum VV or Str. themophilus T101 were grown in a coculture with Lb. delbrueckii ssp. lactis ATCC 15808. These results suggest that G. candidum, like Str. thermophilus, produces formic acid which stimulates the growth of Lb. delbrueckii. Furthermore, a strong heat treatment of the milk base generated the same stimulatory effect on Lb. delbrueckii, as observed when Lb. delbrueckii was grown in the presence of 7.35 mM formate. The results obtained demonstrate that a co-culture of Lb. delbrueckii and G. candidum is based on a synergistic association, and accordingly these two species could be applied together as a starter in the manufacture of “Termoviili”, a novel type of fermented milk product with potential new sensory and nutritional properties.