The "sell-by" and "best-by" dates on milk cartons may soon
become more meaningful and accurate. Cornell food scientists have created a new
predictive model that examines spore-forming bacteria and when they emerge,
according to research published in the Journal of Dairy Science.
"Putting dates on milk cartons is a big issue, because consumers often
discard the milk if it is past the sell-by date," said Martin Wiedmann,
Ph.D. '97, Cornell's Gellert Family Professor in Food Safety and a senior
author of the research. "Often there is little science behind those dates,
as they are experience-based guesses. The goal of this research was to put good
science to use, reduce food waste and reduce food spoilage."
All along the milk production path -- from farm to processing plant to
consumers' refrigerators -- some spore-forming bacteria can survive even the
best pasteurization regimens or the cleanest dairy production plants. The
bacteria can subsequently germinate and spoil milk.
Ariel Buehler, Ph.D. '18, the paper's lead author, said members of the
spore-forming bacillus, Paenibacillus and Viridibacillus genera are ubiquitous
throughout nature. They have been found throughout the dairy chain, including
in farming soil, silage, feed, cow bedding material, milking equipment and in
raw and pasteurized milk. Additionally, the bacteria can survive harsh heat,
desiccation (dryness) and sanitizers. When they have the opportunity to grow in
pasteurized milk, they can cause off-flavors and curdling.
"This is a considerable problem. If we can reduce the spoilage from
spore-forming bacteria -- by reducing their presence and by controlling their
outgrowth -- we can see the shelf life for milk improve from two weeks to
perhaps a month," said Nicole Martin '05, M.S. '10, Ph.D. '19, research
support specialist at Cornell's New York State Milk Quality Improvement Program
laboratory.
The team created a predictive model that characterizes the growth of
psychrotolerant spore-forming bacteria in high-temperature, short-time
pasteurized fluid milk. This baseline model allows milk producers to estimate
shelf life and determine which quality interventions extend fluid milk shelf
life, said Buehler.
Spores can be reduced in microfiltered milk products, which is currently an
emerging trend in the dairy industry, and the research finds that temperature
is a key. The new model showed that refrigerated milk at 39.2 degrees
dramatically lowers the mean concentration of spore-forming bacteria. By
decreasing the refrigeration temperature from 42.8 degrees to 39.2 degrees,
only 9 percent of milk half gallons were spoiled after 21 days, compared with
66 percent of half gallons held at the higher temperature.
Wiedmann imagines a day -- perhaps in five to eight years -- when consumers
find no dates stamped on milk containers. Instead, a scannable barcode could
provide the milk's production history and an accurate use-by date. Cartons
could also sport a time-temperature indicator that communicates shelf-life
prediction. "This is the foundational work that could get us there, where
consumers could manage their food inventory in the fridge," said Wiedmann.
"That's the vision."
Kathryn Boor '80, professor of food science and the Ronald P. Lynch Dean of the
College of Agriculture and Life Sciences, is also a senior author of the study,
"Psychrotolerant Spore-Former Growth Characterization for the Development
of a Dairy Spoilage Predictive Model." The research was supported by the
New York State Milk Promotion Advisory Board through the New York State
Department of Agriculture and Markets.