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Although microorganisms do not grow well at low temperatures, they can grow at typical refrigeration temperatures of 41°F to 5O°F All can grow more rapidly between 41°F and 140°F (doubling in numbers in as little as 8 to 20 minutes).
Consumers also understand that the longer food is left out of the refrigerator the less it lasts. On a basic level, this is a time-temperature relationship. Microorganisms that spoil food grow exponentially faster at higher temperatures, somewhere between a two-to three-fold increase in rate for a 10°F increase in temperature.
Currently, consumers rely on the shelf life date stamped on the package label in their purchases (sorting for the youngest date) and in holding practices at home. Most companies have a "use by" date, a "best if used by" date, a "freeze by" date (on poultry) or a date that says to use within "x" days of date stamped. About 30 states in the USA require such dating, mostly on refrigerated products. These dates give consumers a way to manage their purchases and storage at home in order to ensure the freshness and quality of the food. However; even the most appropriate open date on a food package may be inaccurate-if it is based on the average distribution time for packages and assumes constant conditions, The date does not take into consideration the temperature conditions that an individual product was exposed to throughout the entire distribution chain. This includes the cycling of the unit, defrost, exposure during transfer between refrigeration units, (especially when brought home in the car), and the home refrigeration conditions. Recent reports suggest that temperature control is not being done well, so there can be significant spoilage before the stamped date is reached. The temperature abuse is integrative and cumulative - each step in the distribution chain is critical. A quality product like milk, exposed to one hour abuse at 50°F, will lose about four times more quality than one hour exposure at 35°F. Many refrigerated foods have similar or greater temperature sensitivities because of the high temperature sensitivity for the growth of microbes. One major fresh refrigerated orange juice manufacturer found that 70% of consumer complaints were related to temperature abuse in the control chain.
Temperature Monitoring Systems
There are two major types of temperature monitoring units that can be used to ensure food quality and potentially, safety. One type uses either a mechanical recorder or a computerized recorder/data logger to record the time-temperature history measured at the lip of a probe. These devices measure some point in a distribution container or in a display unit, but they do not measure the temperature at the surface of the food. The data can be downloaded into graphic form to see points of abuse. However, unless a computer program is written to analyze the data from a quality loss standpoint, the graphs cannot tell anything about quality loss since the area under the temperature-time curve (degree-days) is not a meaningful measure obviously these devices have a benefit if the company has a temperature control program. The above mentioned fresh orange juice company was able to eliminate almost 50% of consumer complaints by installing such devices in all transport vehicles and establishing a temperature control program, including accountability and warehouse stock rotation. Unfortunately the other 50% of complaints were not controllable since they occurred in the supermarket and in transport to the home and home storage. The second major type of device is a chemical time-temperature integrator that essentially integrates the exponential behavior of the exposure. it must he designed to have the same temperature sensitivity of the food it is monitoring and is placed (essentially a tape label) on the package surface so that each package has a monitor system it could be designed to show some easily recognizable color change (eg., when an initially lighter area reaches the same color as the outer area surrounding it). Of course, since we would not recognize how fast the color is changing, this must he complimented with some type of open date code. This latter technology has important benefits to the consumer as well as to the food industry and eventually will folIow the other types of temperature monitoring methods.
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