Sugar accumulation in potato tubers is one of the most serious problems for the potato processing industry. Normally, potato tubers are stored at low temperatures (2-4°C) to control sprouting. Storage of potato at low temperatures results in accumulation of reducing sugars (primarily glucose) which leads to “cold-induced sweetening”. Reducing sugars participate in ‘Malliard reaction’ during frying, thus producing dark colored finished product. The suitability of potato tubers for development of processed products such as chips, French fries etc. is mainly determined by the amount of glucose present in potato tubers.
In general, glucose levels below 0.1 % (i.e. 1000 ppm) on a fresh weight basis are acceptable for Chips and French fries production. The surrounding conditions mainly temperature has a great impact on the glucose levels accumulation in the potatoes. As per the normal practice in India, farmers transport their potatoes to the processing industry and upon reaching the industry sites, their potato consignments are rejected by the industry due to their higher glucose content. This put the farmers in a difficult situation and leads to wastage of time and monetary losses in terms of transportation cost and rejection of the tubers. Normally in potato glucose is estimated by various biochemical methods which time taking, tedious, lab based and sophisticated equipment requiring. The method normally followed by industries is the chips colour test. This test usually suggests the suitability of the potato lot for chips/ French-fries making but does not provide any clue that how long the lot can remain fit for making these product.
Keeping this in view, ICAR- Central Potato Research Institute, Shimla has developed “DIPSTICKS” for quick estimation of glucose in potato. The developed “Dipsticks” based method of glucose estimation is highly sensitive (can detect glucose upto 50 ppm concentration), quick (2 - 5 min.), and simple (anyone can perform) and location insensitive (can be performed in potato fields, storage site, home or industrial site). Further, the developed dipsticks are stable for (atleast) two years. These Dipsticks have been found to be working across the cultivars of potato, potatoes under different storage conditions as well as during all the potato tuber developmental stages.
The developed “Dipsticks” for glucose estimation can be used by the farmers (irrespective of their literacy status) at farms or at storage facility or even at the industrial sites. This will help the farmers in taking appropriate decisions for its post-harvest marketing /selling targets/ destinations. This will also be highly useful for vendors having small scale setup for developing processed potato products and to those willing to start the potato processing unit.
Procedure for glucose estimation by the Dipsticks:
The developed method is very simple and fast. Procedure of estimating the glucose in potato tubers using these Dipsticks is as follows.
- Take 2-5 potato tubers randomly from the lot/ field to be tested for glucose levels.
- Make a deep cut on the tuber (approximately till middle of the tuber) with the simple knife.
- Insert the Dipstick through the given cut and wait for 5-10 seconds for potato juice absorption by the dipstick.
- Take out the Dipstick and keep it for 2-5 minutes for reaction to take place (glucose concentration dependent colour development).
- After the 2-5 minutes, compare the developed colour with that of given colour chart,
The colour chart comparison will show the level of glucose in the tested potato. If the level is less than 1000 ppm (parts per million), the potatoes are fit for processing purpose.
(Source: ICAR- Central Potato Research Institute, Shimla)