Influence of droplet size on the antioxidant efficacy of oil-in-water emulsions loaded with rosemary in raw fermented sausages

The oxidative stability of raw fermented sausages containing differently sized oil-in-water emulsions loaded with rosemary extract was studied. For this purpose, rosemary oleoresin was dissolved in Miglyol 812 N (an oxidatively stable triglyceride mixture of caprylic, capric and lauric acid) to a concentration of 100 g/kg, and homogenized using a high shear blender and a high shear blender + high-pressure homogenizer to generate oil-in-water emulsions (10% (w/w) Miglyol 812 N, 2% (w/w) Tween 80, pH 5) loaded with mean droplet size d43 of 0.2 and 4.6 µm, respectively. Unloaded (without added rosemary extract) Miglyol oil-in-water emulsions served as control. The manufactured emulsions were physically stable for 70 days, apart from minor aggregation of the emulsion without incorporated rosemary extract. The addition of 0.48% (w/w) oil-in-water emulsion loaded with rosemary extract into raw fermented sausages retarded lipid oxidation significantly in comparison to sausages loaded with emulsion without added rosemary extract. Moreover, oxidative stability was better at 7 than at 20 °C. Surprisingly, at both temperatures, emulsions with larger droplet sizes were more potent in preventing oxidation than smaller ones. These findings might be caused by the physical location of the phenolic compounds in the oil–water interface of the base emulsions, which makes the antioxidants in rosemary less accessible for preventing lipid oxidation of pork back fat in raw fermented sausages. In addition, the antioxidant effectiveness of the oil-in-water emulsions loaded with rosemary extracts appears to be affected by sausage constituents (e.g., proteins).