Abstract

Pistachio nuts (Pistacia vera L.) are highly sensitive to ambient humidity, and understanding their hygroscopic behavior is essential for optimizing storage and preserving quality. This study investigated the water adsorption properties of pistachio kernels at three temperatures (25 ^°C, 35 ^°C, and 45 ^°C) through experimental testing, utilizing the static gravimetric method. Hygroscopic equilibrium was reached after 11, 9 and 20 days, respectively. The obtained isotherms were classified as type III, high-sugar or high-oil products typically show minimal moisture absorption at low water activity (a_w) levels, followed by a sharp increase in water uptake as the a_w approaches higher values. The adsorption data generated provides essential information for defining optimal storage conditions and preventing quality deterioration during handling, packaging, and distribution. The adsorption data were modeled using three mathematical equations: Guggenheim-Anderson-de Boer model (GAB), Brunauer-Emmett- Teller model (BET), and Langmuir. Among these, The GAB model provided the most accurate fit, showing strong correlation coefficients (R² = 0.995 at 25 ^°C, R² = 0.999 at 35 ^°C, and R² = 0.996 at 45 ^°C). The optimal a_w range that ensures microbiological stability and preserves the quality of pistachio nuts consistently across all three temperatures was between a_w = 0 and 0.2. These findings offer valuable insights for optimizing pistachio storage strategies in controlled humidity environments.

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