Study on Walnut Oil–Fructooligosaccharide Emulsions Fabricated by High-Pressure Microfluidization and Their Application in Improving Rice Quality

The present study aimed to optimize the fabrication conditions of walnut oil–fructooligosaccharide emulsion and evaluate its efficacy in improving the quality of cooked rice. Three food-grade emulsifiers, namely sucrose fatty acid ester (SE), polyglycerol fatty acid esters (PGEs), and diacetyl tartaric acid ester of mono- and diglycerides (DATEM), were adopted to investigate the influences of water–oil ratio, emulsifier dosage, and high-pressure microfluidization (HPM) pressure on emulsion indicators including the emulsion stability index (ESI), particle size, polydispersity index (PDI), zeta potential, micromorphology, and storage stability. The results reveal that SE exhibited the superior emulsifying capacity, with the optimal water–oil ratio and SE dosage determined to be 6:4 and 4% (w/w, based on oil mass), respectively. HPM treatment further reduced droplet size and elevated the ESI, and 150 MPa was identified as the optimal homogenization pressure. Subsequently, the optimized emulsion was applied during rice cooking, with water, pure walnut oil, pure fructooligosaccharide (FOS), simple physical mixture of the two raw materials and crude emulsion set as parallel control groups. Compared with all control treatments, rice cooked with 150 MPa homogenized emulsion possessed the minimum hardness value of 3297.22 and the maximum springiness of 0.74, accompanied by the optimal water retention capacity, luminosity, and the most abundant volatile organic compounds (VOCs). In conclusion, walnut oil–fructooligosaccharide emulsion fabricated via HPM exerted synergistic improvements on the texture and flavor of cooked rice, which could provide a technical reference for the functional modification of staple foods.