Reduce photo-oxidation off-flavor by using iridescent films.

Transparent packaging provides little protection from photo-oxidation--oxidation reactions induced by light--that can lead to the production of off-odor and flavor compounds in food. Light-induced off-flavor in milk is widespread and may be one of the reasons for declining milk sales.

Scientists at Virginia Tech tested transparent iridescent films to see how well they would do in reducing light-induced off-flavor in 2% ultra-high-temperature (UHT) processed milk. Blocking about 95% to 98% of wavelengths of light less than 505 nm appears to reduce the production of light-induced off-flavors. Preliminary data indicate that changes in photochemical reactions may be occurring when certain wavelengths of light are blocked, leading to the production of bitter off-flavors.

Milk, packaged in glass containers with iridescent over wraps, was stored at 4 C under 1600 lux fluorescent lighting for 21 days. Film treatments provided wavelength transmissions of 5% or less at 395 nm to 415 nm, 480 nm to 505 nm, and 525 nm to 565 nm. The researchers also tested four-layer and eight-layer combinations of the films, as well as complete light block and no-light block control treatments.

Experienced sensory panelists ranked the oxidation intensity of the treatments. No significant difference occurred among the various treatments until the seventh day of storage. From that point on, the complete light block control treatment was significantly less oxidized than the control that did not have any light block. The eight-layer combination, four-layer combination, and the 480 nm-to-505 nm blocking treatment led to the lowest off-flavor development for the film treatments. These treatments provided significantly more protection from off-flavor development than did the no-light block control treatment through the 21st day of storage. The 385-nm to 415- nm blocking treatment resulted in the production of bitter off-flavors on the 21st day of the second replication.

The researchers are still working in this area, looking at over-wrap films that provide photo-protective effects for dairy and food products but which also offer product visibility. Researchers are initiating a sensory study to determine if the protective effects provide flavor protection. They will follow this with a consumer acceptability study, if the initial results warrant that value.

Further information. Susan E. Duncan, Department of Food Science and Technology, Virginia Tech, 30 Food Science and Technology Building (0418), Blacksburg, VA 24061; phone: 540-231-8675; fax: 540-231-9293; email: duncans@vt.edu.