Investigating barley protein as an agent of emulsion forming and stability

Background and Objective: Plant-based proteins are considered a suitable alternative to animal proteins due to their efficient use of natural resources, reduced greenhouse gas emissions, and absence of cholesterol. These sources not only minimize environmental impact but also offer nutritional benefits such as improved digestive health, reduced risk of cardiovascular diseases, and the provision of essential amino acids. Among cereals, barley (Hordeum vulgare L.) is recognized as a valuable protein source due to its rich protein composition, resilience to adverse environmental conditions, and the presence of bioactive compounds such as beta-glucans. Barley protein contains a well-balanced composition of essential amino acids, particularly lysine, and exhibits excellent emulsifying capacity and stability properties, making it suitable for industrial applications. In this study, an alkaline extraction followed by isoelectric precipitation was employed to evaluate and optimize the emulsifying capacity and emulsion stability of barley protein.
Materials and Methods: Barley flour was obtained from barley grains and defatted using n-hexane. A suspension of flour and distilled water with the ratio of 1:6 (v/w) was prepared, and its pH was adjusted using sodium hydroxide based on values recommended by response surface methodology (RSM). Following initial centrifugation at 5428 rpm for 15 min, the supernatant was separated, and its pH was adjusted to the isoelectric point using hydrochloric acid. A second centrifugation was performed to precipitate the protein. The resulting precipitate was washed, neutralized, and freeze-dried at -38°C. The emulsifying capacity and emulsion stability of the extracted protein were measured to assess its functional properties. Optimization was conducted using response surface methodology (RSM) with a central composite design (CCD) in Design-Expert software. The effects of independent variables, including alkaline pH (9.5–11.5), isoelectric pH (4.5–5.5), and centrifugation temperature (4–24°C), on response variables were evaluated in 20 experimental runs with six replications at the central point. Statistical analysis was performed using the t-Student test (p<0.05).
Results: Analysis of variance (ANOVA) demonstrated that the quadratic model was statistically significant for predicting the emulsifying capacity of barley protein. The interactive effects of alkaline pH × isoelectric pH, centrifugation temperature × alkaline pH, and centrifugation temperature × isoelectric pH significantly influenced emulsifying capacity (p< 0.05).Similarly, the model was significant for predicting emulsion stability. The interactions of centrifugation temperature × alkaline pH and centrifugation temperature × isoelectric pH had a significant impact on this response variable (p < 0.05). These findings indicate that the quadratic model effectively predicts the emulsifying properties and stability of barley protein emulsions.
During numerical optimization, the independent variables were adjusted within the specified range, and the dependent variables were assumed to achieve maximum efficiency.
Conclusion: The optimal conditions for achieving the highest emulsifying capacity (25.91%) and emulsion stability (24.39%) were identified at a centrifugation temperature of 23.91°C, an alkaline pH of 11.5, and an isoelectric pH of 4.5. Protein extraction was performed under these optimized conditions, and its functional properties were assessed in three independent replicates. The t-Student test indicated no significant difference between the observed and predicted values (t Stat < t Critical).These results highlight that precise control of processing conditions enhances the emulsifying capacity and stability of extracted barley protein. Given the global challenges in protein supply and the advantages of plant-based proteins over animal sources, optimizing barley protein extraction presents a sustainable and efficient approach for the food industries. The findings of this study highlights the way for the effective utilization of plant proteins in the development of innovative food products.
Keywords: Optimization, Barley Protein, Emulsifying Capacity, Emulsion Stability