Abstract
The aims of this study are to revisit the effect of high pressure on homogenization and the influence of pH on the emulsion droplet sizes. The high-pressure homogenization (HPH) involves two stages of processing, where the first stage involves in blending the coarse emulsion by a blender, and the second stage requires disruption of the coarse emulsion into smaller droplets by a high-pressure homogenizer. The pressure range in this review is in between 10-500 MPa. The homogenised droplet sizes can be reduced by increasing the homogenization recirculation, and there is a threshold point beyond that by applying pressure only, the size cannot be further reduced. Normally, homogenised emulsions are classified by their degree of kinetic stability. Dispersed phase present in the form of droplets while continuous phase also known as suspended droplets. With a proper homogenization recirculation and pressure, a more kinetically stable emulsion can be produced. The side effects of increasing homogenization pressure are that it can cause overprocessing of the emulsion droplets where the droplet sizes become larger rather than the expected smaller size. This can cause kinetic instability in the emulsion. The droplet size is usually measured by dynamic light scattering or by laser light scattering technique. The type of samples used in this reviews are such as chocolate and vanilla based powders; mean droplet sizes samples; basil oil; tomato; lupin protein; oil; skim milk, soymilk; coconut milk; tomato homogenate; corn; egg-yolk, rapeseed and sunflower; Poly(4-vinylpyridine)/silica; and Complex 1 until complex 4 approaches from author case study. A relationship is developed between emulsion size and pH. Results clearly show that lower pH offers smaller droplet of emulsion and the opposite occurs when the pH is increased.
Highlights
Homogenizer has been used in the industry such as for pharmaceuticals, food and dairy industry, petroleum and chemical [1, 2]
high-pressure homogenization (HPH) can reduce the size of globules to less than 1 μm and recently, HPH can achieve pressures that exceeding more than 200 MPa [2]
Majzoobi et al (2013) stated that HPH creates a high turbulence and shear, united with compression, acceleration, pressure drop and impact, broke down the particles and dispersed them all over the product [5]. It is efficient for the droplet sizes to be reduced at an elevated pressure of HPH [5, 29,30,31]
Summary
Homogenizer has been used in the industry such as for pharmaceuticals, food and dairy industry, petroleum and chemical [1, 2]. The average droplet sizes for the chocolate and vanilla-powder emulsions at a high homogenising pressure of 100 MPa are 5.11 and 2.48 μm , respectively [5]. For the tomato juice emulsion at medium (50 MPa) and high (100 MPa), homogenising pressure show that the average droplet sizes are the same which is probably due to overpressure (overprocessing) applied on the tomato juice This effects still need to be considered in the study. The samples used in this reviews are such as chocolate and vanilla based powders; mean droplet sizes samples; basil oil; tomato; lupin protein; oil; skim milk, soymilk; coconut milk; tomato homogenate; corn; egg-yolk, rapeseed and sunflower; Poly(4-vinylpyridine)/silica; and Complex 1 until complex 4 approaches from author case study.
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