A survey on yeast microbiota associated with an Italian traditional sweet-leavened baked good fermentation.

Eighty-six yeasts were isolated from samples collected during the productive process of Colomba, an Italian traditional sweet-leavened baked good. They were characterised by phenotypic methods and rapidly identified by RAPD-PCR as Candida milleri and Saccharomyces cerevisiae. Cluster analysis of RAPD-PCR profiles indicated a considerable polymorphism among the isolates. Analysis of fermentation products and sugars revealed high amounts of acetic acid and mannitol after the sourdough fermentation. C. milleri is the dominant species in the sourdough. It is not able to ferment maltose and grows fermenting the glucose released by heterofermentative lactic acid bacteria and supply the bacteria of an electron source (fructose) which increases their cell yield and acetic acid production. This strict cooperation evidenced between lactic acid bacteria and yeasts has important technological and organoleptic consequences. The increased production of acetic acid improves the qualitative characteristics of the leavened dough and of the baked product.