Optimization of enzyme‐assisted aqueous method for the extraction of oil from walnuts using response surface methodology

This work was aimed to optimize an enzyme-assisted aqueous procedure to extract oil from walnuts. Response surface methodology using Central Composite Design was applied to optimize operating conditions that affect the oil extraction process (time, temperature, and water:walnut flesh ratio). Extraction time and temperature did significantly affect extraction yield (R2 = 0.875) and oxidative stability index (OSI) (R2 = 0.531). The predictive capacity of the proposed mathematical surface equation for yield was experimentally tested and its suitability was confirmed under the optimal conditions (41.8°C, 88 min) resulting in 75.4% (experimental) versus 75% (theoretical). Two different experimental conditions were proposed for walnut oil extraction, taking into account the extraction yield and the OSI response surfaces. These walnut oils were compared to that extracted with hexane, resulting in higher quality in terms of OSI (5.27 and 5.12 hr vs. 1.51 hr) and total tocopherols content (685.5 and 575.4 mg/kg oil vs. 269.1 mg/kg oil). 1 Practical applications The purpose of this research was aimed to optimize the oil extraction from walnuts kernels using an enzyme-assisted aqueous procedure. Consumers' interest in walnut oil has noticeably grown due to its functional and nutritional properties. Response surface methodology is an adequate approach to establish the operation conditions of the extraction process. Temperature and time resulted to be the variables that significantly influenced the oil extraction yield, while the water:walnut flesh ratio did not have any significant effect. Two different oils were obtained using those experimental conditions that allowed maximizing the extraction yield and preserving oils oxidative stability. The walnut oils obtained by the proposed enzyme-assisted aqueous extraction methods possessed higher quality than that extracted using organic solvent.