Physical and chemical stability of sweet walnut oil emulsion: Influence of homogenization conditions and stabilizer ratio

In the present study, the effect of homogenization conditions (homogenization rate: 10,000–17,500 rpm; homogenization time: 5–10 min) and stabilizer (polyglycerol polyricinoleate [PGPR]: 1–3% oil content) ratio on the physical and chemical stability of walnut oil in water emulsions was investigated based on CCRD experimental design. Results showed that the incorporation of PGPR led to a decrease in the yield stress, viscosity, centrifuge, and kinetic stabilities up to center point (~2% oil content) and increased after that. The increase in homogenization rate and time, on the other side, brought about an increase in parameters as mentioned above. The induction time of refined walnut oil was 5.46 ± 0.37 hr, while the induction time of prepared emulsions ranged between 6.45 ± 0.29 and 8.29 ± 0.05 hr, which implicitly demonstrated that emulsification led to an outstanding increase in oxidative stability of the emulsion. General acceptance in terms of homogenization rate and time, increased up to center point (~13,750 rpm/7.5 min). PRACTICAL APPLICATIONS: Walnut oil is valuable by‐product of the food industry. It is also a functional food ingredient with its minor bioactive components including tocopherols and phytosterols. However, walnut oil is a rich source of polyunsaturated fatty acids, as well. In this sense, extreme care needs to be taken in order to prevent walnut oil oxidation. In order to meet this challenge, walnut oil was incorporated into o/w emulsion formulation within the present study to retard lipid oxidation and prolong the shelf life of walnut oil by increasing its overall stability. Therefore, the effect of the independent variables selected as homogenization rate, time and stabilizer (PGPR) ratio on physical and chemical properties of the emulsion were investigated.