Relationship Between Kernel Moisture Content and Water Activity in Different Maturity Stages of Peanut

Abstract

Abstract The water activity (aw) and kernel moisture content (KMC) of individual Florunner cv. peanut kernels representing five different maturity stages were measured during a period of late-season drought stress leading up to normal harvest time. Curves were generated describing the relationship between aw and KMC for yellow 1, yellow 2, orange, brown, and black maturity stages as determined by the peanut hull scrape method. As peanuts matured, the KMC for a given aw decreased. KMC in the most immature yellow 1 stage was extremely variable at higher aw levels, indicative of the rapidly changing composition of kernels at that stage. The variation in KMC at high aw decreased with increasing maturity. Equations to predict KMC for given aw showed that KMC varied greatly among maturity stages, particularly at higher aw. For example, at an aw of 0.99 the predicted KMCs for yellow 1 (least mature) and black (most mature) stages were 62.7 and 30.7%, respectively. The degree of variation among stages decreased as aw decreased in response to drought stress. Because preharvest aflatoxin contamination of peanuts is highly dependent on both the maturity stage of peanuts during periods of late-season drought stress and the resulting aw of kernels, these KMC-aw relationships can be utilized in efforts to breed peanuts for reduced susceptibility to aflatoxin contamination by focusing on genotypes that can maintain higher water activities during such late-season drought periods.