Potato

Chemical Composition

Chemical Composition Non Starchy Polysaccharides

Chemical Composition

    The chemical composition of Potatoes depends upon

    • Variety
    • Soil Type
    • Location
    • Cultural Practice
    • Maturity
    • Method of vine killing
    • Storage environment.

    Starch

    • With increase in future growth from 1 cm to 2.5 cm in diameter, the starch gradually increases from 11.4 to 16.0% and from 6.6 to 11.5% with white skin and red skin varieties, respectively (Qudrate - I - khuda et al. 1964)
    • Starch was higher in Potato tubers of 25-30 g than that of 50-80g (Usoltsev et al. 1974)
    • Potato tuber transferred from 320 to 690 F, starch is resynthesized with a simultaneous decrease in the concentration of mono-saccharides and sucrose. During storage of Potato tubes at 400F, a consideration breakdown of starch occurs resulting in a loss of dry matter (Samotus and Palasinski, 1964)
    • Maximum solids and starch occur in the area of the vascular bundle and minimum in the inner pith of the Potato (Zhorovin 1959)
    • Intensity of starch synthesis is higher in Potato plants grown from the basal parts of tubers, which contain about 2% more starch than the apical portions, than in plants grown from apical portion of tubers.
    • Chlorocholine chloride solution applied to Potato tubers before planting or sprayed on plants at bud formation or flowering increased tuber yield and the starch and protein content of the tuber (Fisher and Pyshtaleva, 1974).
    • The components of starch, amylose and amylopectin occur in Potatoes in a ratio of 1:13 (McCready and Hassid, 1974),
    • Starch content of 15 varieties of Potatoes was 13. 7 - 22.2% and amylose in starch was 78.5 - 32.0% (Janicki et al 1967).

    Sugar

    • Sucrose, glucose and fructose comprise the major sugars of the Potato.
    • Large amounts of sugars accumulate during low temperature storage.
    • During reconditioning, the amount of reducing sugars decreases considerably.
    • Small tubers are higher in sugar than big tubers.
    • Tubers from early plantings were lower in glucose and sucrose than those from later planting.
    • Reducing sugars and sucrose increased steadily during sprouting of tubers.
    • Freshly harvested Potatoes contain very little sugar.
    • Reducing sugars accumulate more rapidly than sucrose at low temperatures.
    • Potatoes accumulated negligible amounts of sugar at 60C, greater amounts at 20C, and maximum amounts at 10C.
    • For Potatoes stored at 60 - 20 or 10C., reconditioning was necessary for 2, 4 or 4 week respectively.
    • Rate of sugar loss was not greater for Potatoes reconditioned at 300C than at 200C.
    • Treating Potatoes with ethylene chlorohydrin increase the sucrose content of Potatoes during the first two weeks after treatment. Fructose content increases during the first week, after 28 days it is lower than the untreated. Glucose level rose and fell during four weeks after treatment but rose to the original after the fourth week. (Ginterova, 1959).

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Non Starchy Polysaccharides

Cellulose

  • Present in the cell wall and comprises 10-20% of the non starch polysaccharide of the Potato.
  • It is a mixture of polymers of high molecular weight consisting of glucose residues combined through B-1, 4 linkages.
  • Cellulose content of cell walls is so weakened at 1580 F.

Crude Fibre

  • Consists largely of all wall components including suberin and lignin.
  • Approximately 1% of the dry weight of tubers is crude fibre although extremes of 0.2-3.5% have been found.
  • It increases with maturity and with length of storage.

Pectic Substances

  • Are polymers of galacturonic acid with the carboxyl groups largely methylated.
  • It ranges from 0.7 to 1.5% of the dry wt. of the Potato, the skin being especially high in these substances.
  • Cooking causes on increase in the solubility of pectic materials resulting particularly in a higher pectin content of the water solution fraction following cooking.
  • In a water medium, pectin substances in the cell walls of tubers are altered at 1580F.
  • Treating potatoes with ethylene chlorohydrin increases the sucrose content of potatoes during the first two weeks after treatment.

Hemi-cellulose

  • Are mixed glycosidic chains containing combinations of glucuronic acid with xylose and of galacturonic acid with arabinose.
  • Approximately 1 % of the total crude polysaccharide of the Potato is hemi-cellulose.
  • It largely occurs in the cell wall.
  • Potato also contains ethanol, soluble oligo-saccharide which consists of glucose and fructose residues.

Proteins

  • The proteins of Potato tubers are comprised of about 60-70% globulin and 20-40% glutelin with no albumin.
  • Amino acid composition of glutelin and globulin differs.
  • Amino and composition of protein is independent of the supply of NPK applied to the soil.
  • The amount of protein in Potatoes in about 1-1.5%
  • Potato Protein is practically equivalent to casein in amino acids. In addition, it contains lysine.
  • The total protein consists of 30% tuberinin and 70% tuberin.
  • Tuberin contains adequate amounts of amino acids with the exception of methionine.
  • Addition of N,P,K to stable manure increases protein quality.
  • Greater accumulation of protein occurred when N,P,K as chloride were applied than when N,P.K as sulfate were applied.
  • Nitrogen fertilizations increased the content of total, ammoniumnitrate nonproteins and, in part, protein N of Potato tubers. P and K fertilization had only minor effects on N compounds of the tubers.

Amino Acids

  • 21 amino acids have been identified as normal constituents of the alcohol - soluble nitrogen of Potato tuber tissue which are Cystine, Aspartic and glutamic acids, serine, glycine, asparagine, theonine, alamine, glutamine, alpha amino n-butyric acid, histidine, arginine, lysine, proline, methionine sulfoxide, valine, methionine, isoleucine, Phenylalanine, trylophane and tyrosine (Dent et at , 1947)
  • Potato stored for five months did not change in total nitrogen but increased in amino acids and decreased in NH3 compared with freshly harvested tubers.
  • Potato increased slightly in free amino acids when stored for 2 months at 2.5 to 40C in an atmosphere of 93-96% N, N-6% O and 0.2-2% CO2 as compared to those stored in air.

Organic Acids

  • Citric, isocitric, ascorbic, lactic, malic, tartaric, succinic, oxalic, hydroxymalonic, aconitic, phytic, alpha ketoglutaric, guinic, caffeic, and chlorogenic organic acids are present in Potato (Kroner and Volksen 1950)
  • The principal acids in the juice are citric, oxalic and malic.
  • The total acid content and content of free acids increases in the order in which Potatoes mature being highest for the late maturing varieties.

Minerals

  • The inorganic constituents or mineral content of Potatoes vary with variety, cultural practices, area where grown, maturity, storage and other factors as well as the variability between Potatoes grown under identical conditions.

Inorganic constituents of Potato

Dry basis(Mg. Per 100 gm)
Dry Basis(PPM)
P
43.0-605
Br
4.8-8.5
Ca
10-120
B
4.5-8.6
Mg
46-216
I
0.5-3.87
Na
0-332
Li
Trace
K
1394-2825
As
0.35
Fe
3-18.5
Co
0.065
S
43-423
Ni.
0.26
Cl
45-805
Mo
0.26
Zn
1.7-2.2
-
-
Cu
0.6-2.8
-
-
Si
5.1-17.3
-
-
Mn
0.18-8.5
-
-
Al
0.2-35.4
-
-
    Source: Lampitt and Goldenberg (1940) Lampitt,L and Goldenberg, N. 1940. The Composition of the Potato tubers. Idaho Agr. Expt. Sta. Res Bull 16. Kroner, W. and Volksen W. 1950. The Potato 2nd Edition , Johann Ambrosius Barth, Leip Woodword, C.F. and Talley, E.A. 1953, Review of the nitrogenous constituents of the Potato. Nutritive value of the essential amino acids. Am Potato J. 30 : 205-212. Dent , C.E. Steppa, W and Steward, F.C. 1947. Detection of the free amino acids of plant cell by partition chromatography. Nature 1 60 : 682- 683.

Lipids

  • The average fat content of Potato is aproximately 1.1% an a fresh wt basis ranging from 0.02 to 0.2%.
  • It is greatest in the periderm and lowest in the vascular storage parenchyma and pith.
  • The major fatty acids in Potato tubers are 53% linoleic, 23% linolenic and 12% palmitic and other 12%

Vitamin C

  • Potato is considered to be a good source of vitamin C or ascorbic acid.
  • Tubers grown on peat soil contain less ascorbic acid than those grow on mineral soils.
  • Vitamin C content of Potatoes decreases considerably during the first two months of storage, remains fairly constant thereafter but after six months increases at time of sprouting.
  • The content of vitamin C is higher in Potatoes of varieties of more intense yellow color.
  • The outer part of the tuber has higher a Vitamin C content and central parts have lower concentration.
  • Total content of Vitamin C decreases rapidly after treatment with ethylene chlorohydrin and continues to diminish to a lower level than in untreated tubers.
  • Light apparently has some effect on ascorbic acid formation in tubers. More ascorbic acid is formed closer to the tuber top exposed to light than in the bottom.
  • During sprouting, ascorbic acid concentration increases.

Enzymes

  • Amylase, tyrosinase, phosphorylose, catalase, aldehydrase, polyphenal oxidase, phosphatase, peroxidase, glyoxalase, dehydrogenase, sistoamylase and Zymohexase enzymes have been reported in Potatoes. (Woodword and Talley).
  • The optimum temperature for enzymes which act upon the carbohydrate content of the Potato is not constant with age and period of day.
  • Synthesis of starch in leaves is maximum in day time with it is higher temperature while synthesis in the tubers in higher at night at the prevailing lower temperature.

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Potato

Potato Management