Effect of different oil extraction methods on proximate composition and protein characteristics of walnut (Juglans regia L.) flour

The effect of different oil extraction methods on proximate composition and protein characteristics of walnut (Juglans regia L.) flour were evaluated. Treatments involving hydraulic press with further solvent extraction gave higher protein contents (38.7-38.8 g 100 g−1) than those using screw-pressing at different temperatures (26.9-28.9 g 100 g−1). The major polypeptide patterns from total soluble proteins and glutelin fractions showed minor variations between samples. However, low molecular weight globulins were strongly affected by treatment using hydraulic press followed by solvent extraction, whereas albumins were mostly influenced by temperature conditions used in screw-press extractions. Taking into account that globulins, the second most abundant protein fraction in walnut, is not affected by screw pressing at lower temperatures (25 and 50 °C) and that the flour obtained at 50 °C had the highest protein solubility and a good water holding capacity (3.3 g/g of flour), this process (screw-press at 50 °C) can be considered the most suitable for obtaining partially defatted walnut flour.