Spoilage of vacuum-packed beef by the yeast Kazachstania
psychrophila
A survey of the psychrotolerant yeast microbiota of vacuum-packed beef was conducted between 2010
and 2012. Chilled vacuum-packed beef (n ¼ 50) sampled from 15 different producers was found to have a
mean psychrotolerant yeast count of 3.76 log cfu per cm2
. During this assessment, a recently described
yeast named Kazachstania psychrophila was shown to be associated with this product. In order to gain
basic knowledge about the spoilage potential of K. psychrophila in vacuum-packed beef, challenge studies
were performed and the survival of three different K. psychrophila strains was analyzed during storage of
artificially contaminated beef. Beef samples were inoculated with the yeasts at a contamination level of 2
log cfu per cm2
. Survival and growth of K. psychrophila strains was monitored on malt extract agar at
regular intervals over 84 days. Kazachstania levels rapidly increased about 5 log units within 16 days
under chill conditions (4 C). Gas bubbles were observed after 16 days, while discoloration and production
of off-flavors became evident after 42 days in inoculated samples. This study demonstrates for
the first time, that the psychrotolerant yeast K. psychrophila is a dominant spoilage microorganism of
vacuum-packed beef products stored at low temperatures, causing sensory defects which result in
reduced shelf life, and consequently in considerable economic losses.