Read the
magazine
story to find out more. |
ARS scientists, who
have been studying new technologies to extend the shelf life and enhance safety
of bagged salads, have found that proper storage temperatures minimize
bacterial adaptability inside bags. Click the image for more information
about it. |
|
Cold Temperature is Key to Quality of Bagged
Salads
By Rosalie Marion Bliss
July 24, 2008
Agricultural Research Service
(ARS) scientists have found that proper storage temperatures are essential to
minimize bacterial growth and adaptability inside sealed, bagged salads. They
have been studying the safety of new technologies that extend the shelf life of
bagged salad greens.
The work was conducted by microbiologist
Arvind
Bhagwat with the
ARS
Produce Quality and Safety Laboratory in Beltsville, Md. He first
investigated differences in bacterial growth levels on cut lettuce leaves that
had been bagged under very low oxygen levels--an atmosphere known to extend the
time that bagged salad appears fresh.
Bhagwat investigated whether the lack of oxygen would make it harder
for the bacteria to survive a synthetic gastric juice shock, which mimics the
challenge of exposure to human stomach acids. It turns out that the bacteria
sitting on vegetables packed in low-oxygen atmospheres were more likely to
survive such a shock.
In response to the challenge of being in an air-starved environment,
together with the added nutrients provided by the cut leaves, the bacteria
became hardier during storage. This increased hardiness only took place when
the bagged fresh-cut salad was left at room temperature or unrefrigerated for
extended periods of time.
Bhagwat next tested different temperatures. Bacteria were applied to
fresh-cut lettuce and stored in sealed bags under different atmospheric
conditions for eight days. When stored under very low-oxygen conditions--and
warmer temperatures--bacteria showed more resistance towards synthetic gastric
juice.
The findings underscore a danger involved in inadvertently leaving
fresh-cut produce at temperatures of 59 degrees Fahrenheit or higher,
particularly when low oxygen levels are used to extend the shelf life of fresh
bagged lettuce, according to Bhagwat. Consumers are advised to keep
refrigerator temperatures at 40 degrees F or below, according to experts.
The study was published in the April 2008 issue of the
Journal of Food
Science.
Read more
about the research in the July 2008 issue of Agricultural Research
magazine.
ARS is a scientific research agency of the
U.S. Department of Agriculture.