Texture hysteresis of pistachio kernels on drying and rehydration

To prolong shell life, pistachio kernels are first dried and then in many cases they are rehydrated prior to or during food formulations. Texture of the rehydrated kernels is one of key organoleptic properties for consumer acceptability. In this research pistachio kernels were dried and then rehydrated to different moisture levels to compare the effect of these treatments on their textural properties. This was performed to examine texture differences between pistachio kernels of same water content but different drying, rehydration or thermal histories. Texture profile analysis data showed that hardness, gradient and compression energy of all pistachio samples increased with moisture reduction and significant differences were observed between the textural parameters of dried and rehydrated samples with same moisture level and lower values were obtained for rehydrated samples. It was evident from the results that thermal history of pistachio plays a key role in determining its textural and mechanical properties. Having pistachio kernels of same moisture and different drying and rehydration histories does not guarantee similar textural properties. These findings are clearly showing that texture deteriorations or changes can occur when fruits are first dried and then rehydrated to the initial moisture level. This can have practical implications in developing and designing foods with texture being their main sensory property.