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United States Department of Agriculture

Agricultural Research Service

Title: Irradiation Temperature Influences Product Quality Factors of Frozen Vegetables and Radiation Sensitivity of Inoculated Listeria Monocytogenes

Authors
item Niemira, Brendan
item Fan, Xuetong
item Sommers, Christopher

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 4, 2002
Publication Date: N/A

Interpretive Summary: Four frozen vegetables (broccoli, corn, lima beans and green peas) were irradiated at various frozen temperatures ranging from soft frozen (-5@C) to hard frozen (-20@C) to determine a) the radiation sensitivity of an inoculated outbreak strain of Listeria monocytogenes, b) the effect of changing irradiation conditions i.e temperature, and c) the effect of the recommended radiation dose on the texture and color of irradiated frozen vegetables. The D@ (the amount of radiation necessary to reduce the bacterial population by 90%) for L. monocytogenes differed significantly among the vegetables at each irradiation temperature. D@ increased significantly with decreasing temperature for all vegetables, with each vegetable showing a different pattern of response. At an irradiation temperature of -5@C, D@ ranged from 0.505 kGy on broccoli to 0.613 kGy on corn. At -20@C, D@ ranged from 0.767 kGy on lima beans to 0.916 kGy on peas. On hard frozen vegetables, radiation doses sufficient to kill 99.999 of the bacteria caused significant softening of peas and broccoli stems, but not of corn or lima beans. Lower doses of comparable antimicrobial efficacy delivered in the soft frozen state did not cause significant changes in texture in any vegetable. The color varied significantly among the dose-temperature combinations only for broccoli florets; this variation did not demonstrate a clear pattern of quality changes in response to irradiation. As radiation of a frozen vegetable reduces a population of inoculated bacteria to a target level, the amount of associated radiation-induced softening may be controlled by adjusting the temperature of radiation processing.

Technical Abstract: Four frozen vegetables (broccoli, corn, lima beans and green peas) were gamma irradiated at various frozen temperatures ranging from -5@C to -20@C to determine a) the radiation sensitivity of an inoculated outbreak strain of Listeria monocytogenes, b) the effect of changing irradiation conditions i.e temperature, and c) the effect of the recommended radiation dose on the etexture and color of irradiated frozen vegetables. The D@ (the amount of radiation necessary to reduce the bacterial population by 90%) for L. monocytogenes differed significantly among the vegetables at each irradiation temperature. D@ increased significantly with decreasing temperature for all vegetables, with each vegetable showing a different pattern of response. At an irradiation temperature of -5@C, D@ ranged from 0.505 kGy on broccoli to 0.613 kGy on corn. At -20@C, D@ ranged from 0.767 kGy on lima beans to 0.916 kGy on peas. At -20@C, radiation doses sufficient to achieve a 5-log10 kill (3.9 - 4.6 kGy) caused significant softening of peas and broccoli stems, but not of corn or lima beans. Lower doses of comparable antimicrobial efficacy delivered at -5@C (2.5 - 3.1 kGy) did not cause significant changes in texture in any vegetable. The color varied significantly among the dose-temperature combinations only for broccoli florets; this variation did not demonstrate a clear pattern of quality changes in response to irradiation.

Last Modified: 12/29/2014
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