Gelatinisation of starch

Jenkins, P. J., Donald, A. M. (1998). Gelatinisation of starch a combined SAXS/WAXS/DSC and SANS study. Carbohydrate Research, 308, 133-147. 

Chiang, B Y., and Johnson, J.A. (1977). Gelatinisation of starch in extruded products. Cereal... 

The loss of order during the gelatinisation of starch which was followed using the IR ratio 1047/1020cm 1 is shown in Figure 6 for the mixture of... 

Russell PL (1987) Gelatinisation of starches of different amylose/amylopectin content A study by differential scanning calorimetry. J Cereal Sci 6 133-145 Sadegh-Hassani F, Nafchi AM (2014) Preparation and characterization of bionanocomposite films based on potato starch/halloysite nanoclay. Int J Biol Macromol 67 446 58 Salman H, Blazek J, Lopez-Rubio A, Gilbert EP, Hanley T, Copeland L (2009) Stmcture-function relationships in A and B granules from wheat starches of similar amylose content Carbohydr Polym 75 420-427... 

Figure 9.6 Baking la DSC. DSC trace of a cake batter. Heating rates are 10°C/min for the first (top) and second heating runs. The low-temperature endotherm shows the melting of fat. The mid-temperature endotherm is a combination of the gelatinisation of starch and the coagulation of egg protein, whilst the upper temperature endotherm is due to the melting of the amylose-lipid complex and is reversible. (Taken from [1 7].)...

One of the important properties of starch is that it undergoes gelatinisation. Starch is insoluble in cold water and intact starch granules do not absorb cold water. However, it is possible to prepare a dispersion of... 

The gelatinisation temperature of starch is affected by the presence of sugars, fats and salts. In any practical baked product some or all of these are likely to be present, so the gelatinisation temperature will not be that observed for the equivalent pure starch in distilled water. What is important is that the starch must be gelatinised or the product will collapse. 

On cooking maize starch the viscosity increases when the starch begins to gelatinise. As the temperature rises towards 95°C the viscosity falls. When the paste is cooled the viscosity rapidly increases. The variation of viscosity with temperature is characteristic for each different origin of starch. Potato starch, for example, has a lower gelatinisation temperature than maize starch but has a higher maximum viscosity. When cooled the viscosity of potato starch rises less. Once again amylopectin starches do not show this behaviour as they do not gel. 

Puff pastry is one of the more difficult types of pastry to make. Good puff pastry should rise well and be crisp. Puff pastry is an example of a laminated product. The uncooked dough consists of layers of dough separated by fat. When the pastry is baked the water in the pastry turns to steam that pushes the layers of pastry apart (Figure 1). The heat gelatinises the starch, causing it to set on cooling. 

The solution is to use hot or boiling water in mixing the pastry. This partially gelatinises the starch in the flour as well as melting the fat. A hard fat is used in this sort of product, either lard, the traditional material, or a hard vegetable fat. The hot water could also reduce the activity of some of the enzymes present such as amylase. 

Eclairs are an example of what is called, in English, choux pastry. The pastry is specially made so that it can be piped into shape. The process gelatinises the starch so that the paste has the necessary flow properties to be piped into shape. 

Stevens, D. J. and Elton, G. H. (1971). Thermal properties of starch/water system. Part I. Measurement of heat of gelatinisation by differential scanning calorimetry. Die stiirke. 23, 8-11. 

Jarvis, M. C., MacKenzie, E., Duncan, H. J. (1992). The textural analysis of cooked potato. 2. Swelling pressure of starch during gelatinisation. Potato Research, 35, 93-102. 

Amylases. In the case of pome fruits other enzyme activities are sometimes required. When fruit has been picked before maturity and then ripened under controlled atmospheric conditions in a cool store, there is a likelihood of starch retention originating from the unripe fruit. This starch can become gelatinised during juice processing and can give rise to precipitation and haze effects in the final product. Amylases are used here to break down any residual starch and overcome such problems. 

The blends of starch and a synthetic polymer (usually polyethylene) are products of commercial importance. Two families of blends are obtained those using dehydrated starch pellets and those using gelatinised or thermoplastic starch. In both cases, the mixture with the synthetic polymer is done by extrusion. Further processing by moulding or blowing is still possible, depending on the kind of starch used. 

These are the commonest type of starch used in confectionery and are used to make jellies, pastilles and wine gums. They are made by heating a dispersion of the starch with a small quantity of acid at a temperature below the gelatinisation point, where the effect is to reduce the molecular weight by hydrolysing a few of the bonds. This decreases the viscosityof the starch pastes as might be expected from theory. Starch suppliers have devised a system where these starches are classified by fluidity, where the fluidity is the reciprocal of the viscosity. Thus, in a series of fluidity numbers 20, 40, 60, 75 and 80, the 80 fluidity gives the lowest viscosity paste. 

As usual in most sugar confectionery some control of the texture is achieved by varying the water content of the finished product. In liquorice it is also possible to alter the texture of the finished product by altering the degree of gelatinisation of the starch present in the flour. Traditionally, liquorice was made by cooking in flat-bottomed, well-stirred, steam-jacketed pans. These pans would have the capacity of 500 kg and it would take 2-4 hours to cook the product, the degree of... 

Guy and Home (1998) report a detailed study of expansion as a function of barrel exit conditions. Firstly they note that even under conditions where melting of crystallites of starch should be complete, if shearing conditions are low, expansion is limited to 1-1.5 ml.g specific volume. This implies that for high expansions, the starch must not only be gelatinised but that its component polymers must be exuded into the continuous mass. 

Figure 8.6(a) Schematic drawing of successive shape changes of partly gelatinised wheat starch as seen in the electron microscope. 

Donald model of starch gelatinisation on cooking, (a) in limiting water (b) in excess water. 

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