Potatoes, Tubers, Starches

Discussion in 'Potatoes, Sweet Potatoes, Ray Peat Potato Protein ' started by pete, Sep 24, 2012.

  1. pete

    pete Member

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    Plant Growth & Development - PlSc 401
    http://courses.cals.uidaho.edu/pses/plsc401/

    1) Tuber solids make up about 80 percent of fresh tuber weight. Starch makes up about 70 percent of total tuber solids. Starch is heavier than water, and, therefore, is the primary determinant of tuber density, which is commonly referred to as tuber specific gravity.

    2) Low specific gravity potatoes, typical of red varieties, for example, tend to be best for boiling and canning.

    3) Russet type varieties generally make good all-purpose varieties, but with some exceptions, are best for baking and frying.

    4) Long-white and round-white varieties are divided into those suitable for general home use where potatoes are often boiled, and those that have high specific gravity and are intended only for making potato chips or French fries.

    5) The predominant sugars found in potato tubers are sucrose, glucose, and fructose. Sucrose is formed during photosynthesis and is the sugar used to transport energy to the tubers. Speaking simplistically enzymes in the tubers divide the sucrose molecule into its component sugars—fructose and glucose. Fructose is subsequently converted to glucose, and the glucose molecules are then chained together to form starch.

    6) Potato tubers usually have high sugar content early in their development because the rate of transport from the leaves exceeds the rate of con-version to starch. As the tubers grow and mature, the sugar content decreases, reaching the lowest point when the vines are nearing complete senescence. For the tubers, this point is known as physiological maturity. Tubers left in the field after reaching physiological maturity generally begin to increase in sugars.

    7) The other temperature response that is important to understand is cold induced conversion of starch back to reducing sugars. This can occur in the field or in storage. At temperatures from 50°to 55°F the balance between starch and sugars remains relatively static. As temperatures drop below this range, starch conversion to sugar becomes evident in most varieties. The lower the temperature, the faster the conversion and the higher the final concentration of sugars.

    8) Potatoes that have accumulated excess sugars after exposure to cold temperatures in the field or storage experience a partial recovery toward lower sugar concentrations when exposed to temperatures above 55°F (60°to 65°F is considered optimal).

    9) Potato varieties exhibit large differences in sugar content, especially after storage. For that reason, it is critical to match varieties with intended use. In general, potatoes bred for the chipping industry are lowest in sugars. Potatoes bred for French fry processing typically have intermediate sugar contents, while those bred for the fresh market usually have the highest. Potato breeders are currently making a concerted effort to develop varieties that can be stored at temperatures as low as 40º F and still maintain sufficiently low sugar levels to be used for chip or French fry processing. Several such varieties are now available.

    10) In addition to cold induced stress, a few other conditions in storage can produce an increase in tuber sugars. The most important of these is insufficient air movement. The tuber requires oxygen for respiration and low-level physiological activity. If a pile of potatoes becomes oxygen starved because of infrequent operation of the storage air system or
    because of excess dirt or other air blockage, the normal physiology of the tuber can be disrupted and sugar levels increase.

    11) During tuber growth, the enzyme that converts sucrose to reducing sugars is inhibited. In storage, however, this enzyme becomes active and, if there is a sufficiently large pool of sucrose available, sucrose conversion results in a high level of reducing sugars. Any stress on tubers in storage, such as low temperatures or insufficient air supply, can cause an increase in the sucrose pool.
     
  2. OP
    pete

    pete Member

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  3. narouz

    narouz Member

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    Thanks, Pete!
    Cool info.
    I'm going to have to have another cup of coffee,
    to help me assimilate all that! :P

    But a few things that seem to be sticking...
    1. better to buy varieties that are heavy, as they will contain more sugars.
    2. better to buy young potatoes vs. old (ditto)
    3. store potatoes in frig to increase conversion of starch to sugar
    4. maybe store in a sealed plastic bag, to deprive of oxygen, and thereby increase conversion
    of starch to sugar.

    Ya think?

    Pete, do you have any thoughts about the healthiness or unhealthiness of eating starchy foods,
    from your vantage point--which I take to be Peatian...?
     
  4. OP
    pete

    pete Member

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    Potatoes with high specific gravity will have more starch and are better for frying and baking, those with lower specific gravity have less starch and are better for boiling and canning (red varieties).

    1) High starch content is favored by processors to ensure products have acceptable texture and to keep processing costs down by limiting the amount of raw product needed, the cooking time required, and the amount of oil absorbed. Baked potato products also need high levels of starch to produce the fluffy, relatively dry texture that is preferred by most consumers.

    2) When ex-posed to the high levels of heat, which is typical of the frying process, sugars combine with amino acids and other compounds to form the dark color and flavor we associate with “burned” food.

    3) The reducing sugars glucose and fructose create the most serious problems during frying because they are chemically reactive. Sucrose contributes little to dark color development but is still important because it is the substrate for creating more reducing sugars under the right environmental and physiological conditions.

    Don't forget to scream at your potatoes! Stress seems to help break down starch. :lol:
     
  5. charlie

    charlie The Law & Order Admin

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    OMG, I am on potato overload! :crazy:

    Gonna have to let this soak in another day. Thanks for posting this up!


    :cuss :rolling
     
  6. OP
    pete

    pete Member

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    Starches (polysaccharides), lactose and sucrose (disaccharides) can cause gut irritation if you have problems digesting them, promoting pathogenic germ growth.

    It can't hurt to read about the Specific Carbohydrate Diet and the ideas behind it.

    http://www.breakingtheviciouscycle.info/home/

    http://www.pecanbread.com/

    Don't forget the resistant starch, which is considered the third type of dietary fiber, insoluble fiber and soluble fiber being the other two.
     
  7. Jenn

    Jenn Member

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    You have to CHEW, so as to break down the starch into glucose in your mouth. If you chew sufficiently, there is no irritation. If you inhale, yeah, you are going to have issues. Undigested cellulose breeds bad bacteria. Potatoes, if you peel them, do not contain any cellulose.
     
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