Optimization of Phenolic Compound Extraction from Pistachio Green Hulls: Influence of Blanching, Harvest Time, Solvent Concentration, and Extraction Method

The processing of pistachios results in the generation of a substantial byproduct in the form of underutilized pistachio green hulls. This study aims to identify the most effective strategies for extracting beneficial phenolic compounds from these hulls. The impact of blanching, harvest timing, solvent concentration, and extraction methods on the extraction process was meticulously investigated. The pistachio green hulls were harvested at varying maturation stages during July, August, and September, with blanching achieved through heating the hulls at 80°C for 6 minutes. Extraction procedures involved the use of 100%, 75%, and 50% methanol concentrations, employing techniques such as percolation, Soxhlet, ultrasonic-assisted, and microwave-assisted extraction methods. Quantification of the total phenolic content was conducted using the Folin-Ciocalteu assay. The highest phenolic content was observed in green hulls harvested pre-maturity in July (1887.75mg GAE per 100g), surpassing the content from August and September harvests significantly. Blanching led to a 12% increase in phenolic yield compared to unblanched green hulls. Extraction using 50% methanol resulted in a 46% higher phenolic content compared to 100% methanol extraction. Among the extraction techniques, microwave-assisted extraction demonstrated the highest phenolic yield (3085.30mg GAE per 100g), outperforming other methods significantly. Percolation duration of 5 hours was identified as optimal. These results underscore the significant influence of early harvesting, blanching pretreatment, moderate solvent concentrations, and microwave irradiation in optimizing phenolic extraction from pistachio green hulls. The findings put forth novel insights into the sustainable utilization of abundant pistachio byproducts for the extraction of health-promoting antioxidants.