THE EFFECT OF SORTING FARMERS' STOCK PEANUTS BY SIZE AND COLOR ON PARTITIONING AFLATOXIN INTO VARIOUS SHELLED PEANUT GRADE SIZES

Authors: Whitaker, Thomas; Dorner, Joe; Lamb, Marshall; SLATE, ANDREW - NC STATE UNIVERSITY

Submitted to: Peanut Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/16/2006
Publication Date: 8/10/2007
Citation: Whitaker, T.B., Dorner, J.W., Lamb, M.C., Slate, A. 2007. The effect of sorting farmers' stock peanuts by size and color on partitioning aflatoxin into various shelled peanut grade sizes. Peanut Science 32:103-118.

Interpretive Summary: Aflatoxin is a toxic and carcinogenic compound produced by several fungi and can contaminate peanuts under certain environmental conditions. The U.S. Food and Drop Administration has established aflatoxin guidelines or regulatory limits that should not be exceeded in peanuts and other foods. Aflatoxin contaminated peanuts in a farmers’ loads can be sorted out in the shelling plant as part of the process to produce shelled peanuts. In addition to removing foreign material and the shell, the sheller sorts the peanuts into six grades based upon kernels size. All peanuts in each grade size are color sorted to remove discolored and damaged kernels. A study was conducted to determine how aflatoxin in a farmers’ load partitions when shelled peanuts are sorted into various grade sizes and electronically color sorted into accept and reject categories. Aflatoxin increased as kernel size decreased. The larger kernels had less aflatoxin that the smaller kernels. Electronic color sorters were very effective in removing contaminated kernels from each grade size. Aflatoxin reductions in all grade sizes of about 30 percents were achieved with electronic color sorters. Knowledge of how aflatoxin in farmers’ loads is partitioned into the various grade sizes and color sort categories will help shellers develop more effective management strategies to reduce aflatoxin in peanuts and make a safer food supply.

Technical Abstract: Farmers’ stock peanuts are processed into shelled peanuts using several basic sorting processes. After removal of foreign material and the shelling process, loose shelled kernels and shelled kernels are typically sorted by size into jumbo (J), medium, (M), number one (N1), other edibles (OE), sound splits (SS), and oil stock (OS) grades. Using electronic color sorters, shelled peanuts in each edible grade size are color sorted where discolored kernels are sorted into a reject category and the better quality peanut kernels are sorted into an accept category. Because aflatoxin contamination is associated with both small kernels and with damaged (discolored) kernels, sorting farmers’ stock peanuts by size and by color in the formation of shelled peanuts partitions the aflatoxin in farmers’ stock peanuts in different ways among the various size and color categories. Forty-six 45.4 kg (100 lb) mini-lots, each taken from farmers’ stock lots suspected of aflatoxin contamination, were shelled, sized into six grade categories, and each grade was color sorted for a total of 11 categories (the OS grade was not color sorted) per mini-lot. The aflatoxin concentration among the 46 mini-lots varied from less than 1 ppb to 783 ppb and averaged 73.7 ppb. The aflatoxin in the J, M, and N1, OE, SS, and OS grade sizes averaged 42.5, 66.2, 93.6, 116.7, 105.1, and 133.6 ppb, respectively. Only the two largest peanut grades (J and M) contained less aflatoxin on the average than the farmers’ stock peanuts before sorting by size. After color sorting, the acceptable portion of the J, M, N1, and OE grades had an aflatoxin reduction on the average of 37.8, 30.9, 28.8, and 32.2%, respectively. The aflatoxin in the each grade size (before and after color sorting) was found to be a function of the aflatoxin in the mini-lot. Equations were developed from regression analysis to predict the aflatoxin concentration in each grade size before and after color sorting knowing the aflatoxin concentration in the farmers’ stock lot.