Starch in potatoes

Method 7.12a. Determination of starch in potatoes by hydroiysis and autoanaiysis... 

Shomer, I. (1995). Swelling behaviour of cell-wall and starch in potato (Solanum-Tuberosum L) tuber cells. 1. Starch leakage and structure of single cells. Carbohydr. Polym., 26,47-54. 

Mishra, S., Monro, J. A., Hedderley, D. (2008). Effect of processing on slowly digestible starch and resistant starch in potato. Starch/Stdrke 60 (In press). 

Most of the energy that you get from food comes in the form of carbohydrates. For most of us, starch, found in such foods as potatoes, bread, and rice, is our major carbohydrate source. Sugars—in fruit, honey, candy, and many packaged foods—are also carbohydrates. Plants make carbohydrates, such as the starch in potato tubers, shown in Figure i. 

The starch in potatoes, the cellulose in lettuce leaves, and the glycogen in meat are all polymers of glucose. Cellulose has a linear, unbranched structure that resembles a chain-link fence. Starch molecules can be either branched or unbranched, and glycogen is highly branched. 

Potato BEII was first characterized and found to be a granule-bound protein in tuber starch. In potato, BEII appears to be less abundant than BEI. Both potato tuber BEI and BEII were cloned and expressed in... 

Carbohydrates are found in a wide variety of naturally occurring substances and serve as principal energy sources for the body. Dietary carbohydrates include complex carbohydrates, such as starch in potatoes, and simple carbohydrates, such as sucrose. 

Figure 7.16 A dark bluish-black color is the characteristic result when a solution of iodine encounters the starch in potatoes. What other foods would you expect to give a positive starch test ... 

Starch is a polysaccharide found in many plant species. Com and potatoes are two common sources of industrial starch. The composition of starch varies somewhat in terms of the amount of branching of the polymer chains (11). Its principal use as a flocculant is in the Bayer process for extracting aluminum from bauxite ore. The digestion of bauxite in sodium hydroxide solution produces a suspension of finely divided iron minerals and siUcates, called red mud, in a highly alkaline Hquor. Starch is used to settle the red mud so that relatively pure alumina can be produced from the clarified Hquor. It has been largely replaced by acryHc acid and acrylamide-based (11,12) polymers, although a number of plants stiH add some starch in addition to synthetic polymers to reduce the level of residual suspended soHds in the Hquor. Starch [9005-25-8] can be modified with various reagents to produce semisynthetic polymers. The principal one of these is cationic starch, which is used as a retention aid in paper production as a component of a dual system (13,14) or a microparticle system (15). 

Starches can be separated into two major components, amylose and amylopectin, which exist in different proportions in various plants. Amylose, which is a straight-chain compound and is abundant in potato starch, gives a blue colour with iodine and the chain assumes a spiral form. Amylopectin, which has a branched-chain structure, forms a red-purple product, probably by adsorption. 

Starch is a widely distributed material which occurs in roots, seeds, and fruits of plants. For commercial use, com is the principal source, though wheat and potatoes are also used. Starch is extracted by grinding with water, filtering, centrifuging, and drying, a process which yields starch in a granular form. 

Starches remain a popular glidant, in particular those with the larger grain sizes such as potato starch, possibly because of their additional value as a disin-tegrant in the formulation. Concentrations up to 10% are common, but it should be appreciated that excess may result in exactly the opposite effect of that desired (i.e., flow properties may worsen). Talc is also widely used and has the advantage that it is superior to starches in minimizing any tendency for material to stick... 

Fruits and vegetables Potato, carrot Edible, proteins stable in storage tissues Must be cooked before consumption (potato), high starch content (potato)... 

Starch is a major component of almost all baked products. It most commonly is incorporated into products in the form of wheat flour but various forms of nearly pure starch such as corn flour (maize starch), wheat starch and potato starch are occasionally used. 

In the case of complex carbohydrates the glycemic index is a measure of how quickly the carbohydrate is broken down. An example is to compare potato starch and polydextrose. Both are polymers of dextrose but potato starch in the form of mashed potato is rapidly broken down and causes a surge in blood sugar, i.e. it has a high glycemic index. In contrast, polydextrose, which has the dextrose units linked 1 - 6, a link that is rare in nature, is only 25% metabolised and has a very low glycemic index. 

The variation between the starch from different plants is considerable. The percentage of amylose varies from 27% in maize starch through 22% in potato starch to 17% in tapioca starch. The waxy maizes are unusual in that they are almost pure amylopectin. This is extremely convenient because it avoids the need to separate amylopectin from amylose chemically. 

The xanthan gum, rice starch and potato starch system is available as a mix to be made in domestic bread makers. 

Metabolic Engineering of Starch Biosynthesis in Potato Tubers... 65... 

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