Impact of yeast extracts and peptones on S. thermophilus

Streptococcus thermophilus is heavily used for producing fermented dairy products and there is growing evidence of its probiotic benefits. Because of its complex nutritional requirements, an optimal media composition is key for high growth of the starter culture and maximal outputs per batch.

Standard yeast extract in combination with casein is widely used as a nitrogen source by the starter culture industry for S. thermophilus manufacturing. However, changing labelling requirements (e.g. Vegan, Kosher, Halal), seasonal variation in milk composition and continuous pressure to reduce costs can require substitution of ingredients traditionally used in S. thermophilus production. In the current study we explore the use of yeast derived complex nutrients as a complete solution for S. thermophilus growth and performance.

Main observations

  • Growth of S. thermophilus can be fully supported by solely using yeast based complex nutrients.
  • Optimal media composition with a balanced distribution of free amino acids, nucleotides and peptides can significantly enhance S. thermophilus biomass during starter culture production.
  • Use of the right (combination of) yeast derivatives can enhance cell activity for rapid milk acidification.

Results for S. thermophilus grown on different complex nutrients sources. Here the Colony Forming Units (left) and change in pH of milk during a milk acidification test (left) are shown. The symbols represent the different blends of yeast extracts combined with or without casein peptone.

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