Question

potatoes grown under different level of N can have the same sugar levels but differ fry colours? why?

Answer 1

Air, water, sunlight and soil are the important factors that contribute to plant growth and reproduction. These factors are very much affected by climate (Rainfall, drought ), season and geographical location. Of all these factors, Air provides essential nutrients like Carbon, oxygen etc. Water provides Hydrogen and oxygen.Many plants take up Nitrogen directly from the atmospheres. All though the chief elements needed for structural framework framework is provided by water and air, the remaining 12 essential elements required for plant growth and development is provided by the soil and applied fertilizers. Although plants can absorbe atmospheric Nitrogen, a large part of Nitrogen is also taken up from soil. Hence, the same species of plants growing in different soil types or different parts of the world will have different levels of nutrients available for their growth. The changes in nutrient availablity may be also due to variation in applied inorganic fertilizers. The impact of applied nitrogen (or variation in molecular composition of potato tubers due to difference in nitrogen content) is as follows:

(i) Nitrogen is essential component of Nucleic acids and proteins. Hence, changes in Nitrogen can impart changes in protein content of the crop and its economic product.

(ii) Nitrogen differences in soil will not affect the sugar content of potatoes. This is because, nitrogen has little effect on synthesis of reducing and non reducing sugars. (Infact, phosphorus can affect the reducing sugar content of potato tubers).

The reason for different fry colours of potatoes grown under different Nitrogen availability is as follows:

There is an important reaction called Millard reaction that gives flavour to the fried potatoes (flavouring reaction for all sugar and nitrogen containing baked/fried food). In this reaction, amino acids and reducing sugars in the food material undergoes a rearrangement reaction to form ringed structures that give a characteristic brown colour. This brown colour formation is directly affected by amino acid to sugar ratio. Hence, even though the potatoes grown in different Nitrogen availability areas show same sugar content, there will be changes in aminoacids content. This changes the aminoacids (monomer of protein) to sugar ratio to a great extend, thus showing variation in colour of fried potatoes.