# Critical Review of Techniques for Food Emulsion Characterization
## 3 Techniques for Emulsion Characterization
### Accelerated Stability Testing  
Accelerated stability testing is often employed for rapid analysis of emulsion stability to predict the shelf-life of emulsion-based products and ensure that they maintain their desired properties over time [164]. Acceleration tests can reveal any potential changes in the emulsion properties and stability including the occurrence of separation processes such as creaming, sedimentation, and coalescence within a shorter time frame. This enables researchers and manufacturers to quickly evaluate the effectiveness of the applied formulation and processing parameters and allows more efficient product development [165].  
To accelerate an emulsion instability, it is subjected to mechanical or thermal stress such as heating, centrifugation, shaking, or stirring. These processes provide stimuli, which aim to simulate environmental stresses that may affect emulsion properties during manufacturing, processing, packing, transport, or long-term storage. The most widely used mechanical stress test involves subjecting emulsion samples to centrifugation [166]. The centrifugation test is applicable to fluid emulsions and can be used to separate emulsions under a wide range of forces. It is advisable to run samples at various rates of centrifugation in order to determine rate constants for the process and extrapolate these forces to gravity [167]. In a study by [PERSON] et al. [168], the emulsions were subjected to three 30-min cycles of centrifugation at 3000 rpm. The samples were then examined for signs of coalescence or phase separation. In a recent study, [PERSON] et al. [120] conducted the centrifugal test on oil-in-water emulsions stabilized by whey protein at a speed of 10,000 rpm for 30 min. This study showed that the barrier formed at the droplet interface was able to effectively resist coalescence, even under intense centrifugal forces. Nevertheless, this observation did not provide information regarding the duration over which stability can be maintained. Therefore, this method should be accompanied by other analytical methods for the assessment of emulsion stability over time.  
Thermal stress has a far greater influence on the stability of emulsions than mechanical stress. This is due to a simple relationship between the temperature and a rate constant for the chemical reaction described by the Arrhenius equation [169]. The temperature might induce the changes in viscosity of the dispersed and continuous phases, droplet solubility, partitioning of molecules at the interface, hydration of polymers or colloids, etc. A common thermal stress accelerated stability test relies on subjecting emulsion samples to cooling-heating cycles, where temperature changes between 4 \({}^{\circ}\)C and 40 \({}^{\circ}\)C every 24 h for 7 days [168]. A different approach, known as the freeze-thaw cycle test, involves four cycles of temperature changes between \(-\)5 \({}^{\circ}\)C and 40 \({}^{\circ}\)C every 24 h [170]. In addition to thermal fluctuation, in the freezing stage water is transformed into ice crystals. Therefore,when performing the test, we should consider several factors such as (i) concentration and solidification of free liquid water, (ii) content and precipitation of dissolved substances, and (iii) disruption of the emulsifier layer by ice crystals [167].