PHENOLIC-COMPOUNDS IN PEANUT SEEDS - ENHANCED ELICITATION BY CHITOSAN AND EFFECTS ON GROWTH AND AFLATOXIN B-1 PRODUCTION BY ASPERGILLUS-FLAVUS

Effects of chitosan and Aspergillus flavus to enhance elicitation of phenolic compounds in viable peanut seeds were conducted at two water activity levels. In vitro effects of phenolic acids on A. flavus growth and aflatoxin B-1 production were also studied. Chitosan enhanced elicitation of free phenolic compounds (FPC) at Aw. 85 and .95 levels. A. flavus treatment initially decreased and subsequently increased FPC content, but bound phenolic compounds (BPC) decreased during incubation. Chitosan + A. flavus treatments caused an increase in FPC that reached a plateau between 24-48 h at Aw .85 while BPC levels increased over the same time period at both Aw levels. The major free and bound phenolic acids detected were p-coumaric and ferulic acids and an unknown phenol that eluted at a retention time of 22 min. Generally, chitosan treatment significantly enhanced elicitation of free ferulic and p-coumaric acids and bound p-coumaric acid at Aw .95. Free unknown phenolic and bound ferulic acids at Aw .85 were enhanced by chitosan. A. flavus treatment caused significant induction of bound p-coumaric and ferulic acids and free unknown phenol at Aw .85. Chitosan + A. flavus treatment measure to reduce or eliminate pre-harvest contamination by A. flavus and aflatoxins contributes to sustainable agriculture, especially to developing countries. The enhanced elicitation of preformed phenolic compounds by chitosan may provide seed tissues an additive or synergistic effect in controlling aflatoxin-producing fungi and preventing aflatoxin contamination. Further, such investigation will help elucidate the biochemical basis of elicitor-host interaction that contribute to defensive responses of host tissues. Identification of biochemical factors in induced resistance involves a refinement in the separation and identification of induced phenolic compounds. Methodologies such as spectrophotometric assay or reverse-phase high performance liquid chromatography (HPLC) may be used to evaluate phenolic compound induction by these elicitors. Tn addition, these compounds can be tested on their effects on A. flavus mycelial growth and subsequent aflatoxin production in vitro. Hence, a study on the possible role of phenols on the natural resistance of peanuts to A. flavus invasion was conducted with the following objectives: 1) to quantitate changes in free and bound phenolic compounds influenced by chitosan, A. flavus, and water activity (Aw) levels by Folin-Ciocalteu assay; 2) to separate, identify, and quantitate free and bound phenolic acids influenced by elicitors and Aw levels; and 3) to determine the effects of phenolic acids in liquid cultures at different concentrations on mycelial growth and aflatoxin B-1 production by A. flavus.