Investigation of storage stability in relation to moisture content of peeled whole split pistachio nuts of Gaziantep Variety

Moisture sorption characteristics of peeied whole-split pistachio nuts of Gaziantep variety were investigated at 10, 20, and 30°C using the static method. The sorption isotherms exhibited hysteresis over the range of 0.10- 0.80 water activity which was successfully interpreted using BET, GAB, Oswin, Smith, Henderson, Chung-Pfost and Halsey models and from which the BET, GAB and Oswin models were found to give the best fit. The problem of optimal storage conditions of dry food with sigma- shaped water sorption isotherm was examined mathematically and two approaches were tested. In the first one the experimental data were fitted by the transformed GAB/BET model and the optimal point was calculated by taking the first and second derivatives of the equation. In the second approach, estimates of local slope of the isotherm between adjacent experimental points were calculated. Furthermore, the minimum value of the first derivative was computed. inPistachio nuts were stored at ambient conditions, in air and in modified atmosphere (38 % C02) conditions at 10, 20, 30°C at the monolayer values as previously estimated. The stability of whole-split pistachio nuts were investigated at specified conditions by determining free fatty acid (FFA), peroxide value (PV) and fatty acid composition periodically during 15.5 months as indicators of product stability. It was concluded that high stability of peeled whole-split pistachio nuts was determined under CO2 storage particularly at 10°C. Significant changes were observed in FFA, PV and fatty acid composition when samples stored at ambient conditions. The generated information can be utilized to optimize the packaging and storage parameters for long term storage of peeled whole-split pistachio nuts. Keywords: peeled whole-split pistachio nuts, sorption isotherms, water activity, monolayer moisture content, storage, modified atmosphere, free fatty acids, peroxide value, fatty acids.