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United States Department of Agriculture

Agricultural Research Service

Research Project: CONTROL MECHANISMS FOR MYCOTOXIN PREVENTION IN PEANUTS AND THEIR ROTATION CROPS Title: Effect of Temperature and Relative Humidity on Spotting of Peanuts after Roasting

Authors
item Dorner, Joe
item Butts, Christopher
item Sobolev, Victor
item Sanders, Timothy
item Whitaker, Thomas

Submitted to: American Peanut Research and Education Society Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2007
Publication Date: January 9, 2008
Citation: Dorner, J.W., Butts, C.L., Sobolev, V., Sanders, T.H., Whitaker, T.B. 2008. Effect of Temperature and Relative Humidity on Spotting of Peanuts after Roasting. American Peanut Research and Education Society Abstracts.

Interpretive Summary: none required.

Technical Abstract: A phenomenon commonly known as “spotting” has been recognized for some time in which peanuts that have been roasted and blanched have one or more very dark, distinct, visible discolorations. Spotting is assumed to be associated with some form of damage, but a small percentage (< 2%) of spotted seed in a shelled, roasted lot is generally considered unavoidable and acceptable. In recent years an unusually large number of shelled lots has been found to contain unacceptably high (> 2%) levels of spotted seed. This increase in spotting could relate to conditions that seed are exposed to after shelling and during shipment to end users, or it could be associated with increased length of farmers’ stock storage that exposes peanuts to the higher temperatures and relative humidities of the summer months. The objective of this study was to determine the relationship of various combinations of temperature and high relative humidity to the presence and/or development of spots. In a series of separate experiments, shelled and unshelled peanuts were placed in an environmental chamber controlled at different temperature and relative humidity combinations. Replicate 300 g samples were taken at various time intervals during each experiment to determine fungal colonization and percent spots after roasting. Results showed that highly significant increases in both fungal load (cfu/g) and spot percentage occurred during extended exposures, and the rate of spot development was associated with increasingly higher temperature/relative humidity combinations. Exposing shelled peanuts to a temperature of 26.7 C and 80% RH for 11 days produced an exponential increase in spotting that is described by the following equation: y = -1.35 + 0.82 ex/3.16, (r2 = 0.971), where y is the % of spotted peanuts and x is the number of days. Fungal colonization of peanuts as measured by total cfu/g also increased exponentially producing an r2 of 0.963 (equation not shown). Reducing either the temperature or RH increased the time necessary for a similar increase in spotting to occur. For example, at the same temperature but a RH of 72%, 37 days were required to produce the same percentage of spotted seed as were produced in only 8 days at 80% RH. An increase in colonization of peanuts by fungi capable of growing at relatively low water activity occurred during the exposures of peanuts to the adverse conditions, particularly where the testae were broken. These data confirm that exposure of peanuts to relatively high temperatures and humidities is most likely responsible for the increase in spotting and illustrate the need to monitor temperature and relative humidity conditions during storage and shipment of peanuts so that adjustments can be made to prevent spotting.

Last Modified: 12/17/2014