| 1. |
- Johansson, Dorota, et al.
(författare)
-
Sintering of fat crystal networks in oils
- 1995
-
Ingår i: Food Macromolecules and Colloids. - : Royal Society of Chemistry. ; , s. 418-425
-
Bokkapitel (refereegranskat)abstract
- 1.1 Semisolid Fats Foods like margarine, butter and chocolate consist of semisolid fat, in a continuous phase, which determines the product properties such as consistency and stability. Semisolid fat consists of colloidal fat crystals, with high melting points, dispersed in a liquid oil with a low melting point. Most natural fats demonstrate a broad spectrum of melting points such that small to moderate variations in temperature may start melting or postcrystalization processes of some components. Extensive changes in product character and quality occur as a result. These changes may be especially critical for low fat foods where the amount of fat and/or saturated (solid) fat is close to the necessary limit for creating proper texture and stability. 1.2 Adhesion Sources Crystals in semisolid fat form a network due to mutual adhesion in which adhesion strength determines structure and consistency. Dispersion (van der Waals) forces are not strong enough to account for the network strength observed experimentally [1]. Therefore, other adhesive forces, for example water bridges, must occur [2]. Formation of water bridges results in as an increase in the yield value of semisolid fat upon the addition of small amounts of water (figure 1).
|
|
| 2. |
- Johansson, Dorota, et al.
(författare)
-
Water-in-triglyceride oil emulsions. Effect of fat crystals on stability
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 939-950
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of low concentrations (0.1-5%) of fat crystals on the stability of water-in-soybean oil emulsions was examined by light scattering and sedimentation experiments. Both initial flocculation/coalescence rate and long term stability against water separation were determined. The initial flocculation/coalescence rate increased upon addition of very small amounts of fat crystals. When the crystal concentration was increased over a critical concentration (specific to a system), a decrease in the flocculation/ coalescence rate occurred. The increased flocculation/ coalescence rate is likely the effect of bridgening of water droplets by fat crystals. Fat crystal wetting by water is an important criterion for this phenomenon to occur. Emulsion stabilization for crystal concentrations over critical is caused by a mechanical screening of water droplets. The presence of considerable amounts of crystals in oil also lowered the density difference between droplet and medium, and enhanced viscosity. The degree of increase in viscosity depended upon emulsifier. Both decrease in density difference and increase in viscosity play a role in hindering flocculation/ coalescence of droplets. In long term studies of water separation, all concentrations of fat crystals stabilized the w/o emulsions. The droplet size of these emulsions increased likewise until the critical droplet size was approached, when the screening effect of crystals on droplets stabilized the emulsions. The stabilizing effect for emulsions with monoolein was continuously improved by increasing the amount of crystals up to 5%. For lecithin stabilized emulsions, an optimal effect was achieved for fat crystal concentrations of 1-2%.
|
|
| 3. |
- Johansson, Dorota, et al.
(författare)
-
Wetting of fat crystals by triglyceride oil and water. 1. The effect of additives
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 921-931
-
Tidskriftsartikel (refereegranskat)abstract
- Wetting of fat crystals has been extensively examined in this work by contact angle (0) measurements of fat crystal, oil, and water in three-phase contact. Contact angle was measured in oil. The crystals were nonpolar and wetted by oil for a contact angle equal to 0°, and polar and wetted by water for an angle equal to 180°. Fat crystals are expected to contribute to the stability of margarine emulsions if they are preferentially wetted by the oil phase (0° c 0 < 90°), but result in instability if they are preferentially wetted by the water phase (90°
|
|
| 4. |
- Johansson, Dorota, et al.
(författare)
-
Wetting of fat crystals by triglyceride oil and water. 2. Adhesion to the oil/water interface
- 1995
-
Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 72, s. 933-938
-
Tidskriftsartikel (refereegranskat)abstract
- Fat crystals influence the stability of food emulsions such as margarine, butter or cream if adsorbed to oil/water interface. During the adsorption process, a new fat crystal/water interface is created while the oil/water interface is lost. The driving force for adsorption is therefore the difference between the interactions fat crystal/water and oil/water. In this work we have estimated this interaction difference and compared it to displacement energy for fat crystals from the oil/water interface to the oil. Our calculations have shown that fat crystal adsorption to the oil/water interface (expressed by contact angle Q) is determined by polar energy, excess fat crystal/water over oil/water (Isw-Iow). The interfacial tension constitutes the resistance force for crystal adsorption to the interface. Polar interaction energy fat crystal/water is stronger than polar interaction energy oil/water in all cases examined (Isw-Iow>0). The difference corresponds to about 104-106 hydrogen bonds for a hypothetical fat crystal with a diameter of 1 µm. Displacement energy for fat crystals to oil, is lower than polar energy excess in most cases examined. Thus, an additional interaction between fat crystals and oil make it easy to displace the crystals to the oil. There is also a relationship between adhesion tension (-gow·cosQ) for the crystals at oil/water interface, and the interfacial tension gow. A straight line of a slope -1 is achieved for systems with low interfacial tensions (gow) and low polar energy excess (Isw-Iow).
|
|
