Effects of Pretreatment on the Yield of Peanut Oil and Protein Extracted by Aqueous Enzymatic Extraction and the Characteristics of the Emulsion.

Effects of comminution on peanut particle size and yield of peanut oil and protein were analyzed. Additionally, the emulsion properties (surface protein concentration, particle size, and ξ-potential) were compared. Moreover, different demulsification methods were used to investigate the emulsion stability. Results showed that the yield of peanut oil and protein was highest (87.23% and 82.05%, respectively) after dry comminution for 72 s. Upon wet comminution for 120 s, the yields of peanut oil and protein were 89.91% and 84.70%, respectively, which were both significantly higher than that obtained after dry comminution (p < 0.05). The surface protein concentration and ξ-potential of emulsion made by dry comminution (DCE) were 7.02 mg/m2 and 12.08 mV, respectively, and those of emulsion made by wet comminution (WCE) were 10.71 mg/m2 and 15.25 mV, respectively, which were significantly higher than that of DCE (p < 0.05). The volume average particle size of DCE was 3.41 µm, which was significantly higher than that of WCE (3.18 µm, p < 0.05). Collectively, these results indicated that WCE was more stable than DCE. Further, the demulsification rate of DCE was significantly higher than that of WCE when treated by freeze-thawing, pH, papain, and phospholipase A2 (p < 0.05). Demulsification effect of Alcalase 2.4L was the best among these five demulsification methods treated, and the demulsification rate of DCE reached 92.77%, which was slightly higher than that of WCE (92.67%), further illustrating the higher stability of WCE.

Effect of Papain on the Demulsification of Peanut Oil Body Emulsion and the Corresponding Mechanism.

This study investigated the effect of papain on the demulsification of peanut oil body emulsion extracted using an aqueous enzymatic method and the associated mechanism. The highest free oil yield using papain (92.39%) was obtained under the following conditions: an enzymatic hydrolysis temperature of 55°C, sample-to-water ratio of 1:3, enzyme concentration of 1400 U/g, and an enzymatic hydrolysis time of 3 h. Papain degraded the peanut oil body protein to small-molecular-weight peptides (≤ 14.4 kDa). Compared to the emulsion before enzymatic hydrolysis, the amino acid content in the aqueous phase was higher after enzymatic hydrolysis, the viscosity of the oil body emulsion was lower, and the particle diameter of the emulsion was significantly larger. The following demulsification mechanism was derived. Papain degrades the protein on the peanut oil body and dissolves it in water. The outer side of the oil body loses the protection of electrostatic repulsion and steric hindrance provided by the membrane protein. This causes the viscosity of the emulsion system and the molecular steric hindrance to decrease. As a result, the oil droplets gather and eventually demulsify. The results of this study provide the theoretical basis for the instability in oil body emulsions and are expected to promote the application of enzymatic demulsification in industry.