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Postharvest Handling and Storage of Potato

Potato has emerged as fourth most important food crop in India after rice, wheat and maize. Indian vegetable basket is incomplete without Potato. It is an important part of breakfast, lunch and dinner worldwide. India is one of the highly populated nations in the world and to feed all of its population, no crop other than potato can make an impact. Currently India is the third largest producer of potatoes in the world. The production level of the country hovers around 47 million tonnes. The major potato growing states are Uttar Pradesh, West Bengal, Punjab, Bihar, Haryana, Madhya Pradesh, Gujarat and Maharashtra. More than 90 per cent potato crop is grown in winter season (Rabi) under assured irrigation facility from October to March. The rest is being taken up during rainy season (Kharif). This article elaborates the significance of postharvest operations on quality of potatoes.

During harvesting of potatoes, following practices are to be considered-
1. Follow the practice of dehaulming cutting of haulms / aerial parts by sickle or destroying by machines, when the crop attains 80-90 days and when the aerial part of the plant turns yellow.
2. Always harvest in dry weather.
3. Stop irrigation about two weeks before dehaulming.
4. Avoid bruising and skinning of tubers otherwise tubers become susceptible to rot diseases.
5. Harvest the crop after 10-15 days of haulm cutting.
6. Harvesting can be done by tractor drawn potato digger or manually with help of spade or khurpi.

Drying and Curing
The harvested potato should be cured in the field. For optimum suberisation, curing is essential for healing the wounds of tubers resulted from cutting and bruising during harvesting. Expose to sun causes the greening of potatoes. Always dry the harvested tuber in storage shed. All the damaged and diseased tubers should be removed during sorting.

Handling and packaging of potatoes are done generally on farm. After harvesting, the tubers are kept in a heaped condition temporarily and covered with straw. After a few days, sorting is done for separating the diseased and cut tubers. The sound tubers are packed in hessian cloth bags or nettlon bags. The Ordinary hessian bags are used for packing potatoes with a capacity of 80 kgs, 50 kgs and 20kgs. The nettlon bags made of plastic net are used to pack 25 kgs potato and preferred for export purpose.

Storing potatoes for longer period in normal temperature is not possible as it is a living material and through respiration, the changes occurs due to heat, resulting in loss of dry matter and ultimate deterioration of quality of tubers. At optimum condition, the quality of potatoes remains good in storage for 3-5 weeks. The best temperature and humidity condition for storage of potatoes are as follows:

The different grades of potato as suggested by Directorate of Marketing and Inspection, Faridabad are as under:
Grading plays an important role in marketing of potato. The potato should be packed in different bags as per recommended grades before marketing. Potato marketing in India suffers from severe constraints like wide price fluctuations, existence of large number of middlemen, storage and transportation bottlenecks and lack of other marketing infrastructures. Indian potato marketing system is not efficient, integrated and is not in a position to face the emerging challenges of potato production and utilization. Studies on marketing margins or price spread reveals that as the number of market functionaries increases, they add cost to the commodity in the marketing channel which results in the fall of producers show in consumer’s rupee. Farmers are advised to make their own cooperative groups or Farmers Producers Organisations and follow standard postharvest handling practices for self-marketing of produce. Various Government agencies like National Horticulture Board, National Horticulture Mission and Ministry of Food Processing and Industries provide financial assistance for creation of postharvest and cold chain infrastructure for horticultural crops.

Storage of potato with CIPC applications: A potential technology for potato processing
Potatoes are mostly produced during the winter season from November to March, but are consumed year-round. Therefore, storage of potato under optimum conditions is very important part of supply chain in order to avoid glut like situation in the market. Problems of potato during storage are: Sweetness, sprouting, and decay.

In general practice, the seed and ware potatoes are stored by the farmers at low temperature (0-3-degree C), which is ideal for suppressing sprouting, but physiological changes at this temperature results in accumulation of sugars in the tubers, giving sweetish taste resulting in lowering the culinary qualities of stored potatoes as well as making them unfit for preparation of French fries. Thus, the stored potatoes fetch lower price in the market compared to ‘Pahari’ potatoes from hilly areas. Storage of potatoes at high temperature (10 ± 2-degree C and 90-95 per cent RH coupled with application of sprout- suppressant chemicals like CIPC is a viable technology, which can enhance the storage life, maintain the low sugar levels and improve culinary/ processing qualities in the potatoes during storage.

What is CIPC?
Chlorpropham (Isopropyl – N (3- Chlorophenyl carbamates), popularly known as CIPC, is an effective sprout inhibitor. It acts by blocking the process of cell division (mitosis). In store, CIPC is currently applied as a hot fog of fine solid particles (of the order of 5μm in diameter) on the potatoes. The mechanism of action of the applied chemical is believed to involve volatilisation of the deposited solid and subsequent transport of the vapour to the eyes of the tubers inducing the required sprout suppression. This chemical currently is being marketed in India by United Phosphorus Ltd., Mumbai under the brand name ‘Oorja’. This commercial formulation is said to contain 50 per cent active ingredient (a.i.) and 40 ml of this formulation is required for fogging of one tonne of potatoes.

Procedure for CIPC application
The disease free fully cured, mature tubers are loaded in the cold storage and temperature is maintained at 18.3-degree C during loading.
1. Temperature of the storage is brought down from 18.3-degree C to 10-degree C gradually in one week.
2. Chlorpropham fog is injected @ 40 ml/tonne using DYNA fogging machine into the storage chamber loaded with potatoes. The first fogging is done at the first sign of sprout growth and second fogging is done 60 days later.
3. Refrigeration is not used when CIPC fog is flushed into store. For this, the refrigeration unit is switched off prior to, during and upto 40 hours after the treatment. Then doors are opened for half an hour after 40 hours to flush out the accumulated gases. Thereafter the temperature of cold storage is maintained at 10 ± 1-degree C and 90-95 per cent RH.
4. The chamber should be completely leak proof to ensure that there is no loss of refrigeration during storage period; otherwise there will be more consumption of electricity to maintain uniform temperature.
5. Humidity should be maintained at 90-95 per cent level inside the chamber to avoid shrinkage in the treated potatoes. Humidifier should be installed to get optimum humidity level.

Important points to keep in mind for storage of potato
Air circulation: The air circulation inside the storage chamber during the loading of potato and pull-down period should be minimum 50 CFM/MT of Potato (85 CMH/ MT of Potato).
Relative humidity: Maintaining high relative humidity (95 per cent RH) in storage is very important to prevent tuber dehydration. It helps to control the total shrinkage loss.
Ventilation of cold stores: Always ventilate the storage chambers periodically. Atleast, 2 to 6 air changes per day is good enough to maintain desirable level of CO2 level less than 4,000 ppm inside the storage room.
Storage cleanliness: Disinfection or cleaning of the storage facility is a good practice in all storages and is essential for seed producers. Cleaning of the store must be completed in time for the new harvest to begin.

Dr B V C Mahajan,
Senior Horticulturist
Punjab Horticultural Postharvest Technology Centre
Punjab Agricultural University Ludhiana, Punjab

Dr. Swati Kapoor,
Assistant Food Technologist
Punjab Horticultural Postharvest Technology Centre
Punjab Agricultural University Ludhiana, Punjab

Dr. Ritu Tandon,
Assistant Chemist
Punjab Horticultural Postharvest Technology Centre
Punjab Agricultural University Ludhiana, Punjab