Refrigerated products may undergo changes in sensory qualities before food safety or microbiological properties are compromised. Consumers may even interpret off-flavors as a potential health risk.

Researchers at rtech Laboratories, a business unit of Land 'O Lakes, St. Paul, Minn., can analyze organoleptic problems and recommend practices to keep foods tasting fresh.

“Sometimes our customers are very focused on food safety, and they only want microbiological tests,” says Lori Simzek, business development manager, sensory evaluation services, consumer research. “We suggest customers also look at shelf life sensory tests because a high quality product is so important. Consumers perceive refrigerated foods as fresher and companies can get a higher value for them.”

For example,“Milk may look fine, but it develops off-flavors,” she says. “It is very susceptible to temperature changes in the distribution, retail and in-home areas.”

Sensory problems may also arise due to exposure to oxygen and to light oxidation. Water activity in the product may cause premature sensory problems.

People tasting fluid milk experience the problem as oxidized or rancid flavors and off-aromas. A trained taste panel describes it as a “cardboard” flavor. The sweet cream notes may be absent and the milk may taste flat rather than fresh.

Sometimes appearances are affected, as with butter sticks that are a darker yellow on the outside surface than the inside, or cottage cheese that separates. These physical changes correlate to flavor changes.

Sensory panelists at rtech analyze products according to a schedule, depending on the product. For example, milk is tested three times a week while cheddar cheese is evaluated once a month. Trained panels perform blind tastings and use descriptive analysis and acceptability testing. When the panel gives two data points in a row below the acceptable level, product failure has occurred. Consumer guidance panels furnish additional information.

Setting up experimental storage conditions has proved helpful, Simzek says. The lab has light chambers to test products for light-initiated oxidation. The effects of different storage temperatures on products also has been studied. The proper refrigeration temperature is below 41° F, but the company also runs tests at 45° F to see how products react.

The lab participated in a 1999 U.S. Cold Temperature Evaluation syndicated study of food storage temperatures from the supermarket case to the consumer's refrigerator. Conducted by Audits International, the results indicated half of the products are stored above 41° F in supermarket refrigerated cases and some products are even stored above 45° F. The study recommended that food companies factor in the possibility of higher storage temperatures when designing product shelf lives.

How can a company keep its product fresh-tasting throughout its shelf life? “Light chambers are helpful in looking at packaging barriers to protect against light oxidation,” Simzek says. “Gallon jugs can be coated to make them opaque and paper cartons can be coated for an oxygen barrier.” Researchers also look at the formulation of the product to see if slight modifications may help.

Simzek stresses companies pay attention to developing tight controls on product conditions before releasing the items. A company has to look at its own distribution system and work with its logistics department to optimize handling and storage and to prevent temperature abuse. “Sometimes, we recommend a shorter shelf life, in the best interest of product quality,” she says.

Simzek is working with ASTM's E18 Sensory Committee to develop guidelines on how to evaluate shelf life, a project intended to help companies with their own standards.