An Investigation of the Effects of the Addition of Pistachio Hull and Testa on the Oxidative Stability of Pistachio Butter

Introduction: Pistachio butter is susceptible to autoxidation owing to its high content of unsaturated fatty acids. Materials and Methods: In this research, the effects of pistachio hull and testa (0.0, 0.5, and 1.0%) on the oxidative stability of pistachio butter have been investigated. The peroxide value, oxidative stability (using the rancimat method at 110°C), and the refractive index (at 30°C) were evaluated after months 0, 2, and 4 from the storage time at 25°C. Results: The peroxide value of the samples increased with an increase in the storage time. The lowest peroxide value was related to the treatment containing 1.0% of hull and 1.0% of testa. Besides, in the oxidative stability test, the control sample and the treatment containing 1.0% of hull and 1.0% of testa showed the lowest and highest stability time against oxidation, respectively. The refractive index of the samples was determined within the range of 1.464-1.470. According to the results, there was a significant difference just between the control samples of month 0 and month 4, being an indicator of polymerization reactions. There was no significant difference among other treatments at different storage times. Conclusion: Pistachio butter containing the combination of 1% of hull and 1% of testa showed higher oxidative stability after 4 months of storage.