Fat crystals

D. Now the ether will be a deep reddish yellow. Distill off the ether...quack...and take the temp up to 170 C to drive off any other volatiles. Should recover 90%+ of the original weight of oil. Now add 500 ml of saturated bisulfite and stir for 1.5 hours...Quack Vacuum Filter, the duck fat crystals Wash with water and ether, yield dull fine ppt in the filter cake...stable bisulfite addition product...can be stored forever...QuackU Yield -50 to 80% depending on a ducks technique ... 

Nucleation tempering of the stiU molten fat is necessary because the cocoa butter, if left to itself, can soHdify in a number of different physical forms, ie, into an unstable form if cooled rapidly, or into an equally unacceptable super stable form if cooled too slowly, as commonly happens when a chocolate turns gray or white after being left in the sun. The coarse white fat crystals that can form in the slowly cooled center of a very thick piece of chocolate are similarly in a super stable form known in the industry as fat bloom. 

D Rousseau. Fat crystals and emulsion stability—a review. Food Res Inter 33(1) 3—14, 2000. 

The structure of butter and other dairy spreads are further complicated by the presence of aqueous phase droplets and intact fat globules. Water droplets tend to weaken the structure and fat crystals inside intact fat globules cannot participate in the formation of a network thoughout the product (Chapter 3). 

Excellent review of the physics of fat crystallization useful in interpreting the results of these measurements. 

The structure (e.g., number, size, distribution) of fat crystals is difficult to analyze by common microscopy techniques (i.e., electron, polarized light), due to their dense and interconnected microstructure. Images of the internal structures of lipid-based foods can only be obtained by special manipulation of the sample. However, formation of thin sections (polarized light microscopy) or fractured planes (electron microscopy) still typically does not provide adequate resolution of the crystalline phase. Confocal laserscanning microscopy (CLSM), which is based on the detection of fluorescence produced by a dye system when a sample is illuminated with a krypton/argon mixed-gas laser, overcomes these problems. Bulk specimens can be used with CLSM to obtain high-resolution images of lipid crystalline structure in intricate detail. 

The principal cause of poor image quality using CLSM is poor dissolution of the dyes, especially Nile Blue. In the method as described, Nile Red co-crystallizes with the fat crystals and, thus, a higher resolution of crystal surface is obtained. However, it is difficult to distinguish solid from liquid fat with only Nile Red. Nile Blue is necessary because it is dissolved in the liquid phase and provides fluorescence for contrast. As a result, the quality of images is very much improved. The disadvantage of Nile Blue is its low solubility. Special attention should be paid to sufficiently dissolving the dye at 60°C. 

Marangoni, A.G. and Hartel, R.W. 1998. Visualization and structural analysis of fat crystal networks. FoodTechnol. 52 46-51. 

Figure 2 Fat crystallization of bulk fat and emulsified fat of ice cream mix with (+E) and without (-E) emulsifiers after cooling to 5°C measured by pNMR.

Crystallization of supercooled fat in topping powders may be studied by NMR afterreconstitution in heavy water. Below room temperature spontaneous fat crystallization takes place under isothermal conditions in the presence of effective emulsifier (PGMS) but not with ineffective emulsifiers or without emulsifiers (Figure 4). 

The time scale of fat crystallization is much shorter for topping powders than for ice cream mix as presented in Figure 2. This is due to the much higher emulsifier content in topping powder. The induction of fat crystallization in whippable emulsion systems is due to interfacial protein desorption from the fat globules of the emulsion mediated by the emulsifiers. This phenomenon is described in section 3.1. 

Other methods to study fat crystallization in whippable emulsions may be used, e.g., a recently developed technique using ultrasonic velocity14. 

The structure of whipped topping is thus completely different from that of whipped dairy or liquid imitation creams. In the latter systems the air bubbles appear to be covered in a monolayer of fat globules, which are rarely deformed and which protrude with a substantial part of their volume into the air phase of the bubbles. If large fat crystals are present, they are considered detrimental to foam stability, in contrast to whipped toppings6 (Figure 7). 

Figure 7 Left Surface of air bubbles (a) in whipped topping emulsion is completely covered with a thick layer of plate-siiaped fat crystals (c). w = water phase. Right Surface of air bubbles (a) of whipped imitation cream is covered with a monolayer of only slightly destabilized globules (f). Reprinted from reference 22, courtesy of Scanning Microscopy International.

The viscosity range varies, depending on the whippable emulsion system in question. In whipped toppings viscosity increases as soon as the topping powder is reconstituted in cold water. This is due to the formation and aggregation of hydrated fat crystals which will... 

Localized NMR spectroscopy, which is often called as MRS in comparison with MRI, is not so familiar technique in food science, because a specific pulse sequence such as ISIS and a facility which can precisely follow the pulse sequence without any contamination from other position is needed for localization of position. The localized NMR is usually used together with NMR imaging. The study of solid/liquid ratios, fat structure and polymorphism and the kinetics of fat crystallization was reviewed [24], The potential of applications in food process development and control was offered. The localized spectra of sausages in areas of 0.3 mm X 0.05 mm (thickness of sample =1.5 mm) were obtained by the spin echo 2DFT method [113], in which the difference in the tissue structure was discussed with relation to the process and original materials. McCarthy et al. determined mobility of water in foams by using a localized spectroscopy [114]. T2 relaxation time varies in the foam as function of diameter and its variation was analyzed by the classic 2-state fast exchange model. 

Powders often have a stabilizing effect on emulsions [548], To understand the responsible effect we have to remember that a particle assumes a stable position in the liquid-liquid interface if the contact angle is not zero (see section 7.2.2). Upon coalescence of two drops the solid particles would have to desorb from the interface. This is energetically unfavorable. A common example of the stabilizing contribution of solid particles are margarine and butter. Both are water-in-oil emulsions. The water droplets are stabilized by small fat crystals. 

In food science, ice crystals play a role in stabilizing ice cream, while fat crystals play a role in stabilizing whipping cream. It should be emphasized that in practice the contact angles should neither be too high nor too low, or else the partides will remain in the water or oil phases, respectively, and not stabilize an emulsion [297]. Although there are many exceptions to such rules they remain useful for making initial predictions. The particles used for emulsion stabilization have to be much smaller than the size of the emulsion droplets they are intended to stabilize so the particles are usually quite small, typically less than 1 pm in diameter. 

Some products, like butter and margarine are stabilized by fat crystals. Salad dressings and beverage emulsions are stabilized by other emulsifiers. The stability of non-protein stabilized food emulsions, involving lower molar mass type molecules, tend to be better described by the DLVO theory than are protein-stabilized emulsions. An example of an O/W emulsifier whose emulsions are fairly well described by DLVO theory is sodium stearoyl lactylate [812],... 

Many other baked products, such as cakes, originate as both W/O emulsions and foams. Cake batter comprises a mostly W/O emulsion, with some O/W domains, that is also a foam containing small-sized air bubbles. Initially, the air bubbles are stabilized mostly by fat crystals. As the baking process gets underway the fat melts,... 

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