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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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