Yayoi Miyagawa

Destabilization of mayonnaise induced by lipid crystallization upon freezing

The thermal and rheological history of mayonnaise during freezing and its dispersion stability after the freeze-thaw process were investigated. Mayonnaise was cooled to freeze and stored at −20 to −40 °C while monitoring the temperature; penetration tests were conducted on the mayonnaise, which was sampled at selected times during isothermal storage at −20 °C. Significant increases in the temperature and stress values due to water-phase crystallization and subsequent oil-phase crystallization were observed. The water phase crystallized during the cooling step in all the tested mayonnaise samples. The oil phases of the prepared mayonnaise (with rapeseed oil) and commercial mayonnaise crystallized during isothermal storage after 6 and 4 h, respectively, at −20 °C. The dispersion stability was evaluated from the separation ratio, which was defined as the weight ratio of separated oil after centrifuging to the total amount of oil in the commercial mayonnaise. The separation ratio rapidly increased after 4 h of freezing. This result suggests that crystallization of the oil phase is strongly related to the dispersion stability of mayonnaise. Graphical abstract Temperature changes during storage at −20 °C and separation ratio, X, after the freeze-thaw process of commercially available mayonnaise.

Effect of oil droplet size on activation energy for coalescence of oil droplets in an O/W emulsion.

The activation energy of a reasonable order of magnitude was estimated for the coalescence of oil droplets in an O/W emulsion by formulating the balance of forces acting on a droplet that crosses over the potential barrier to coalesce with another droplet by the DLVO theory and Stokes’ law. An emulsion with smaller oil droplets was shown to be more stable.

Effects of Vegetable Oil Type and Lipophilic Emulsifiers on the Induction Period of Fat Crystallization

The induction period of crystallization, which is defined as the time required for oil to start to crystallize, is useful indicator of the freeze-thaw stability of food emulsions such as mayonnaise. We investigated the induction period of vegetable oils with low melting points, such as rapeseed and soybean oils, which are commonly employed for mayonnaise production. The induction period was measured by monitoring the temperature of a specimen during storage at low temperature. The induction period depended on the type of oil and lipophilic emulsifier, emulsifier concentration, and storage temperature. The effect of the oil type on the induction period depended on the composition of the oil. Differential scanning calorimetry (DSC) analyses of the lipophilic emulsifiers suggested that the melting trend of the emulsifier is strongly related to the induction period.

Dispersion Stability of O/W Emulsions with Different Oil Contents Under Various Freezing and Thawing Conditions

Freezing and thawing of oil-in-water (O/W) emulsion-type foods bring about oil-water separation and deterioration; hence, the effects of freezing and thawing conditions on the destabilization of O/W emulsions were examined. The freezing rate and thawing temperature hardly affected the stability of the O/W emulsion. O/W emulsions having different oil fractions were stored at temperatures ranging from -30 to -20 °C and then thawed. The stability after thawing depended on the storage temperature, irrespective of the oil fraction of the emulsion. A good correlation was found between the time at which the stability began to decrease and the time taken for the oil to crystalize. These results indicated that the dominant cause for the destabilization of the O/W emulsion during freezing and thawing is the crystallization of the oil phase and that the effects of the freezing and thawing rates on the stability are insignificant.

Dispersion and oxidative stability of O/W emulsions and oxidation of microencapsulated oil

Oil-in-water (O/W) emulsions are among the dispersion systems commonly used in food, and these emulsions are in thermodynamically unstable or metastable states. In this paper, various methods for preparing O/W emulsions are outlined. Since the commodity value of food is impaired by the destabilization of O/W emulsions, experimental and theoretical approaches to assess the stability of O/W emulsions are overviewed, and factors affecting the dispersion stability of emulsions are discussed based on the DLVO theory and the concept of the stability factor. The oxidation of lipids in O/W emulsions is unhealthy and gives rise to unpleasant odors. Factors affecting the autoxidation of lipids are discussed, and theoretical models are used to demonstrate that a reduction of the oil droplet size suppresses or retards autoxidation. Microencapsulated lipids or oils exhibit distinct features in the oxidation process. Models that explain these features are described. It is demonstrated that a reduction in the oil droplet size is also effective for suppressing or retarding the oxidation of microencapsulated oils. Graphical abstract Methods for preparing O/W emulsions, experimental and theoretical approaches to assess the stability of O/W emulsions, and factors affecting the oxidative stability of lipid in O/W emulsion and microencapsulated systems are described.

Liquid–solid phase equilibria and the frozen ratio of ternary aqueous solution of acetic acid and sodium chloride

ABSTRACT In this study, we obtained the liquid–solid phase diagrams of a ternary solution of sodium chloride, acetic acid, and water, and a diagram of the frozen ratio of this ternary mixture. Based on the data from differential scanning calorimetry (DSC) measurement, the phase equilibria of this ternary system were successfully visualized. The formation of the ternary eutectic phase occurred between −34°C and −35°C, and the formation of the binary eutectic phase was suggested around −22°C to −34°C. Higher concentrations of a component had a significant effect on the phase equilibrium. A diagram of the frozen ratio of the ternary solution of sodium chloride at −20°C was also obtained by a simple temperature measurement method. This diagram is useful for estimating the ice fraction at the phase equilibrium of a frozen food system containing sodium chloride and acetic acid.