What does it happen when a bacteriophage infects a sourdough microbial population?

A phage infection is a real risk in food plants since viruses are able to quickly destroy bacterial population, stopping the fermentative process. Actually the manufacture of sourdough products based on traditional batch technology is less involved in this phenomenon than dairy or wine productions. By now the main belief is that the presence of several different strains and the selection of spontaneous phage-resistant mutants can explain the ability of natural mixed cultures to overcome viral infections. In this work the propagation of Lactobacillus sanfranciscensis phage EV3 in solid sourdough, liquid sourdough and cultural medium was investigated. Lactobacillus sanfranciscensis H2A strain and the Candida humilis 21R strain were used respectively as phage host culture and yeast culture; different experiments were carried out at 25°C for 24 hours. In solid state (Dough Yield = 160) the averages of increase of dough volume and pH variation between the infected and the uninfected doughs found out to be identical. Either for yeasts and for lactobacilli counts no significant difference were observed between concentration mean values in infected and control samples, at all different times (o “at all the tested times” o “at different times”). During incubation, yeasts augmented of 1.2 log cycles while lactobacilli of 2.0 log cycles; a scarce phage multiplication (1.5 log cycles) was observed without causing any variation in fermentation parameters. In liquid sourdough (Dough Yield = 320) the changes of pH between the infected and the uninfected samples were very similar; the growth of yeast population (1.2 log cycles) was not affected by phage infection. Also for lactobacilli counts no significant differences were detected between mean values of infected and control tests, but there was an increasing of only 1.0 log cycle. The phage concentration rises of 3,0 log cycles