Valutazione della qualità dei sieroinnesti: confronto tra le tecniche classiche e quella conduttimetrica

In a 5-month study, 2 natural whey starters for Parmigiano Reggiano cheese and 4 (2 natural and 2 commercial) for Grana Padano were analysed monthly or weekly. Conventional microbial enumeration methods, using phase-contrast microscopy, MRS agar or milk, and direct conductimetry, with results expressed as DT (detection time), were compared. The starters, microscopically homogeneous in respect of cell type and amount, differed in viability. There were fewer viable cells in commercial starters than in Parmigiano Reggiano starters. Commercial starters always presented a characteristic conductimetric curve. Poor-quality starters had clearly higher DT values, but with traditional methods there was no quality discrimination. During storage of starters for up to 7 days at room temperature, DT values increased with time, whereas bacterial counts showed no significant change