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Comparison of milk iodine concentration between retail conventional and organic milk in the United States.

M. Ghelichkhan



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Comparison of milk iodine concentration between retail conventional and organic milk in the United States.
M. Ghelichkhan*2, L. H. P. Silva2, R. C. R. Tinini1, J. G. Dessbesell1, M. A. Zambom1, A. F. Brito2. 1Universidade Estadual do Oeste do Paran� Marechal C�ndido Rondon, Brazil, 2University of New Hampshire Durham, NH.

Previous research showed that over 50% of organic dairies in the Northeast and Upper Midwest US feed Ascophyllum nodosum meal known to be a rich source of iodine (I). Therefore, milk I concentration (MIC) in retail organic milk may be greater than that of conventional milk. Further, different feeding practices between organic and conventional dairies have been shown to seasonally change MIC, which can be also affected by processing method. However, a comprehensive survey of conventional and organic retail MIC has not been conducted in the US. A total of 299 samples of 2%-reduced fat organic [n = 96; ultra-high temperature (UHT), n = 62; pasteurized, n = 34] and conventional (n = 203; UHT, n = 25; pasteurized, n = 178) milk were purchased in selected grocery stores (n = 73) in June 2017 (summer) and March—April 2018 (spring) from the 11 northeastern states and Washington DC (n = 23 cities visited). No duplicate brand (n = 108) or milk plant (n = 82) was included in the MIC data set. Statistical analyses were done in JMP Pro 15.0.0 using a full factorial ANOVA model that included season (summer vs. spring), production system (conventional vs. organic), and milk processing (UHT vs. pasteurized) as independent variables, as well as interactions. A season by production system interaction (P < 0.001) was observed; while conventional milk tended to have greater MIC (P = 0.09; 388 � 17 μg/L) than organic (341 � 22 μg/L) during the summer, organic milk had increased MIC (P < 0.01; 515 � 21 μg/L) compared with conventional milk (437 � 16 μg/L) in the spring. This seasonal difference likely results from intake of I-binding goitrogens present in pasture that prevent the transfer of I into milk. UHT milk also had greater MIC (P < 0.01; 455 � 16 μg/L) than pasteurized milk (386 � 12 μg/L). Note that organic milk had greater MIC during winter than conventional milk and most was UHT processed, indicating that our milk processing data should be interpreted cautiously. Overall, season and processing appear to affect MIC as shown in previous research, and MIC was generally below the 500-�g/L threshold considered safe for consumers.

Keywords: dairy food, milk plant, milk processing.