Biochemical analysis of potato

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BACKGROUND

Potato or Solanum tuberosum L. is a vital tuber crop all over the world and is an important part of our diets. The second biggest producer of potato is India. In the recent years it has become a challenging food crop along with maize, wheat and rice. Potato can produce double the mount of dry matter as produced by wheat, rice and maize. The processors look after some important parameters like sugar level, dry matter, starch content and phenol content.

So, the objective of this test is biochemical analysis of potato.

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REQUIREMENTS

Sample:          Potato tubers

Chemicals:     Potassium oxalate

    Ethanol

    Potassium hydroxide

    Sodium carbonate

    Perchloric acid.

Reagents:       Copper tartarate reagent

    Arsenomolybedate reagent

    Anthrone reagent

    Folin-Ciocalteau reagent

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PROCEDURE

Sampling of potato tubers for biochemical analysis

Collect the tubers and wash it properly. Then air dry it and remove the peel with the help of hand peeler. Then after peeling properly cut longitudinally cut out a thick slice of the potato tuber from the centre from bud end to stem end. Then take this slice and cut it into three equal pieces lengthwise. Then from these three pieces cut breadth wise again into three pieces. Take the central portion as pith. Then take a fine blade and cut the bud end, stem end and the central portion into cortex and medulla in the presence of sunlight for separation of vascular ring. The cutted portions will be chopped finely and are analyzed for various biochemical properties.

Dry matter

For determining the dry matter content first, the finely chopped tuber pieces are dried in oven at a temperature of 70^oC for about six hours and then at a temperature of 65^oC till consistent weight is achieved.¹

Reducing sugar

Reducing sugar is estimated by Nelson Somoyogi procedure as described by Sadasivam and Manikam.² The principal behind this is that copper oxide is formed when reducing sugar is heated in the presence of alkaline copper tartarate. The cuprous oxide is then reacted with arsenomolybdic acid that reduces molybdic acid to molybdenum blue. So, at first the prying compounds like proteins are first removed by method of precipitation utilizing potassium oxalate solution, then filtration and then centrifugation. The resultant supernatant (0.2 ml) is mixed with alkaline copper tartarate reagent and then the mixture is boiled for about 10 min, allowed to cool down and then to it Arsenomolybedate reagent (1 ml) was added. The blue colour which will be formed will be then measured photometrically.

Sucrose

The analysis of sucrose was done by method as described by Anthrone.³ Mix 80% ethanol extract (0.1 ml) and 30% aqueous potassium hydroxide (0.1ml) and then keep this mixture for about 10 min in boiling water bath. Allow this mixture to cool down and add 3ml of Anthrone reagent and keep it for about 10 min at 40^oC. Then the absorbance was measured at 620 nm. A known concentration of sucrose was taken as standard.

Phenol

The estimation of phenol content was based on the principle that phenol in the presence of Folin-Ciocalteau reagent reacts with phosphomolybdic acid in an alkaline medium and forms a blue colour complex. So, from the sample phenols were extracted in the presence of 80% ethanol. Then centrifuge it and the supernatant was evaporated for drying and then final volume was made to 1 ml. To this Folin-Ciocalteau reagent (1 N) was supplemented along with 20% sodium carbonate (2 ml). The blue colour complex that was formed was measured for absorbance at 650nm against a blank reagent.⁴

Starch

To about 500 mg pf sample 80% alcohol was added for removing sugars and then extraction of starch was done with 52% perchloric acid. Then centrifuge it and treat the supernatant with perchloric acid and make the final volume to 100 ml. About 0.2 ml of the extract was taken and to it 4 ml Anthrone was added and was put to boil. Then a dark green colour complex was formed which was measured for absorbance at 630 nm.

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CONCLUSION

The distribution pattern of all the biochemical parameters depends on the intersecting set of factors that includes tuber anatomy, loading and unloading of phloem and xylem and the tuber transport mechanism. The estimation of this biochemical pattern helps in enhancement of required constituents levels through breeding or agronomy.

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REFERENCES

1. Borzenkova RA, Borovkova MP. Developmental pattern of phytohormone content in the cortex and pith of potato tubers as related to their growth and starch content. J Plant Physiol. 2003;50:119–24.
   
2. Burton WG. Yield and content of dry matter. The underlying physiological processes. In: WG B (ed) The Potato. Longman Scientific and Technical, New York; 1989: 84–155.
   
3. Sadasivam S, Manikam A. Estimation of reducing sugars by Nelson-Somoyogi method. In: Sadasivam S, Manikam A (eds) Biochemical methods for agricultural sciences. Wiley Eastern Ltd, New Delhi, India; 1996a: 5–6.
   
4. Sadasivam S, Manikam A. Phenols. In: Sadasivam S, Manikam A (eds) Biochemical methods for agricultural sciences. Wiley Eastern Ltd, New Delhi, India; 1996a: 193–194.