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

Abstract

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). Practical applicationsThe 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.

Characteristics and Antioxidant Activity of Walnut Oil Using Various Pretreatment and Processing Technologies

“…It proved that pretreatment had a negative effect on the processing of walnut oil by SP. The lipid yield of AEE oil in our study was lower than that of the report (75.4%) [ 34 ], which might be because the reaction conditions of AEE were not optimized. The lipid yield of AEE oil would improve by properly optimizing the experimental conditions.…”

Effects of different antioxidants and their combinations on the oxidative stability of DHA algae oil and walnut oil

“…This phenomenon is closely related to the pretreatment and refining processes of raw oils (Chen et al., 2011 ). Before refining, crude DHA algae oil needs to be fermented from microalgae and then obtained after cell lysis and centrifugation (Yin et al., 2018 ), while crude walnut oil can be obtained from walnut kernels (60%–65% levels of oil) directly (González‐Gómez et al., 2019 ). It can be seen that the extraction process of DHA algal oil is complex and tedious than that of walnut oil, which may result in its higher concentration of such minor components, and then requires a stricter refining process further.…”

Walnut (Juglans regia L.) oil chemical composition depending on variety, locality, extraction process and storage conditions: A comprehensive review

“…To develop an effective and eco-friendly technique for walnut oil extraction, a surfactant and salt-aided aqueous extraction method was also used to break the emulsion (Geng et al, 2020), with an oil recovery rate greater than 90%, and a possibility of reusing the demulsifier. An enzyme-assisted aqueous procedure was optimised to extract oil from kernels and obtain walnut oils of higher quality, in terms of oxidative stability and tocopherol content, than organic solvent extracted oils (González-Gómez et al, 2019). At the present time, the optimisation of solvent extraction processes to increase yield performance is no longer studied, because consumers are increasingly looking for less processed products.…”