Submitted to: Food Research International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/31/2025
Publication Date: 2/4/2025
Citation: Atci, S., Bilbao-Sainz, C., Mcgraw, V.S., Wood, D.F., Mchugh, T.H., Rubinsky, B. 2025. Investigating the effects of freezing temperature and oil content on the physiochemical characteristics and stability of oil-in-water emulsions under isochoric freezing conditions. Food Research International. https://doi.org/10.1016/j.foodres.2025.115906.
DOI: https://doi.org/10.1016/j.foodres.2025.115906

Interpretive Summary: Oil-in-water emulsions are known to undergo instability upon freezing and thawing, often resulting in partial degradation such as oil separation. This study aimed to investigate the effects of isochoric freezing (IF) and conventional freezing (CF) on the stability and physicochemical properties of emulsion samples containing 10% and 20% oil. IF was conducted at -5 °C/59 MPa and -20 °C/170 MPa, while CF was performed at -5 °C and -20 °C under atmospheric pressure (0.1 MPa). Our findings revealed that subjecting the emulsions to IF (-20 °C/170 MPa) effectively reduced microbial counts to below the detection limit, whereas CF did not result in a significant reduction in microbial counts. Additionally, the particle size of CF 10% and 20% emulsions increased, while there was no significant change or a slight increase in the particle size of IF 10% and 20% emulsions, respectively. Furthermore, the viscosity of CF emulsions was significantly higher compared to control and IF emulsions. CF samples stored at -5 °C for 1 day exhibited the highest yellowness among all samples. These results suggest that CF emulsions were not stable to the freeze-thaw process, as evidenced by significant increases in mean particle diameter, degree of flocculation, coalescence, apparent viscosity, and yellowness. In contrast, IF (-20 °C/170 MPa) demonstrated potential to improve the physical stability and microbiological aspects of oil-in-water emulsions. Overall, these findings underscore the potential of IF as a promising technique for enhancing the stability of oil-in-water emulsions during freezing and thawing processes.

Technical Abstract: Oil-in-water emulsions are inherently unstable systems and can be affected by environmental factors such as temperature changes, including cooling and freezing. The objective of this study was to examine the impact of isochoric freezing (IF) on the stability and physicochemical properties of emulsion samples containing 10 % and 20 % oil. The IF process involved placing emulsion samples in IF chambers at thermodynamic equilibrium conditions, specifically at temperatures of -5 °C/59 MPa and -20 °C/170 MPa. In contrast, conventional freezing (CF) was conducted at the same temperatures of -5 °C and -20 °C but at atmospheric pressure (0.1 MPa). 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.