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Chemical reactions at low temperatures
In the early stages of the T-TT research it became apparent that many
of the changes accompanying food deterioration on prolonged storage, even
at extremely low temperatures, were caused by the continued action of
the food’s own enzymes. Even before the T-TT work began, it was known
that better frozen food quality results from blanching, the process in
which vegetables are briefly heated in hot water or steam. The intent
is to deactivate the enzyme peroxidase, thought to be the culprit in causing
the post-freezing degradation. T-TT studies led to a rapid, reliable,
and convenient assay for peroxidase, and subsequently established the
appropriate blanching parameters for individual fruits and vegetables.
As the range of foods tested in the T-TT work expanded, it became apparent that the elimination of peroxidase activity was neither necessary nor desirable during the blanching of some foods. In some cases, the index of blanching became the inactivation of catalase, a process that was gentler than that required for peroxidase inactivation. In other cases, yet another enzyme, lipoxygenase, was found to be the major promoter of reduced quality, and blanching times were considerably shorter for this enzyme. In other words, what was once thought to be a single and simple blanching process was now expanded to included detailed procedures for different foods, all of which contributed to a higher food quality for the consumer.
Early methods of food preservation | A chance discovery | Frozen food chemistry | U.S. Agriculture turns to science | Frozen food research begins at WRRC | Defining "Quality" | Chemical reactions at low temperatures | Chlorophyll as a benchmark | Major scientific results from the T-TT program | Societal impact of the T-TT program | Landmark designation | Further reading and acknowledgments
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