Moisture-equilibrium relative humidity relationships in pistachio nuts with particular regard to control of aflatoxin formation.

Adsorption and desorption isotherms have been determined both manometrically and by weight equilibration for Turkish pistachio nut kernel, shell and hull. Comparison of the calculated and experimentally determined adsorption isotherms for whole nuts showed good correlation. Nuts inoculated with Aspergillus flavus conidia were equilibrated to various ERH levels and stored in controlled environment cabinets at 28°C. Competitive growth of xerophilic strains of A. amstelodami prevented growth and aflatoxin production by the A. flavus at ERHs of 86% and below. At 88% ERH marked aflatoxin production occurred but competition was observed between the A. flavus and A. niger. In sealed containers metabolic moisture from growth of A. amstelodami raised the ERH from the initial 85% and permitted toxin production by A. flavus. The results are discussed in relation to post-harvest handling and storage of pistachio nuts.