Investigating the effects of freezing temperature and oil content on the physiochemical characteristics and stability of oil-in-water emulsions under isochoric freezing conditions

Abstract

Oil-in-water emulsions are inherently unstable systems and sensitive to environmental factors such as temperature changes. This study evaluated the effects of isochoric freezing (IF) on the stability and physicochemical properties of emulsions containing 10% and 20% oil, comparing IF at −5 °C/59 MPa and −20 °C/170 MPa to conventional freezing (CF) at the same temperatures under atmospheric pressure (0.1 MPa). Emulsions were kept in IF chamber and conventional freezer at −5 °C and −20 °C for 3 days. This study analyzed microbial count, microstructure, globule size, zeta potential, viscosity, color, and stability of emulsion samples after 3 days of CF/IF. Our findings indicate that after subjecting the emulsions to IF (−20 °C/170 MPa), the counts of total aerobic microorganisms, yeast, and mold were below the detection limit. However, CF did not lead to a significant reduction in the microbial count in the emulsions. The globule size of CF 10% and 20% emulsions increased, with slower freezing rates leading to more significant increases in globule size. In contrast, we observed no significant change and a slight increase in the globule size of IF 10% and 20% emulsions, respectively. The viscosity of CF emulsions was significantly higher than that of control and IF emulsions. CF samples at −5 °C exhibited the yellowest color among samples. Our results indicate that CF emulsions were not stable to the freeze–thaw process, evidenced by a significant increase in mean globule diameter, degree of flocculation, coalescence, apparent viscosity, and yellowness. Overall, these findings suggest that IF (−20 °C/170 MPa) could effectively improve the physical stability and microbiological aspects of oil-in-water emulsions.