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Dr  Sarath Ilangantileke *

1. Introduction

1.1 The current status of post-harvest handling and processing

Potato production in the Asia and the Pacific region is increasing and is significant in China and India, which rank first and third in terms of amount produced and area cultivated in the region, respectively. However, although production and area in the Asian and South Asian countries are increasing compared to the Western potato growing countries, post-harvest handling and processing practices need to be improved to achieve the ultimate goal of adding value to excess production. Despite the large production areas, high productivity and large total amount produced in the bigger producing countries in the region such as China and India, the processing of potatoes accounts for only a small percentage of the total crop produced. Although processing activities in India, China and some other countries in the region are increasing, the percentage of potatoes processed at present is very low compared to Western countries. In Asia, except for a few large multinational and locally-owned companies in India and China, potato processing is limited to the small-scale and medium-scale potato chip or flake producing plants of local entrepreneurs in the potato-producing countries such as Bangladesh, Pakistan, Republic of Korea, etc. In the West, and other potato-growing countries such as Russia, processing is a vital and highly profitable part of the potato chain.

The potato is gaining popularity in all Asian producing countries. Research and development activities are mainly taken care of by the national potato organizations, and in a limited number of countries multinationals and national private organizations are involved in processing related research and development of the crop system. Although all countries emphasise increased production, in general issues related to the post-harvest handling and processing of potatoes receive little emphasis. These issues are complicated in that factors that control the quality of processed potato products vary. Many products could be processed using existing potato varieties and production techniques, but yields and outputs of processed products are very low mainly because of a lack of good processing potato varieties that could be grown in the countries themselves. In addition to the non-availability of processing varieties, the lack of facilities for the entire processing chain in countries other than India and China, hinder the development of the processing industry.

1.2 Poverty in the region and its alleviation

Many potato-producing countries in Asia and the Pacific region are listed as countries having populations below the poverty line of US$1 per day. South Asian and West Asian countries have over 500 million people living on less than US$1 per day and countries in Southeast Asia and the Pacific have populations of over 200 million living on less than US$1 per day, although the trend now seems to be reducing. Although large-scale potato cultivation is seen in the larger producing regional countries, many poor small farmers also cultivate small areas of potatoes. Many of these farmers lie below the poverty line and are at the mercy of traders and other market forces and have to dispose of their freshly harvested crops at low prices immediately after harvest when large quantities of potato are available in the market. Farmers who can store the freshly harvested produce at the best possible condition for sale at a later period will obtain better prices for their crop. They will also have an opportunity to add value to the harvested potatoes, thereby obtaining higher incomes. This will help them evade a situation of compulsion to sell at low prices immediately after harvest, resulting in reduced incomes. In addition, interventions to keep the produce in good condition for longer periods will help farmers reduce quality and quantity losses after harvest and make available more food for their communities.

1.3 Solution to improving farm incomes of potato farmers

Increased incomes for poor potato farmers will help them move above the existing poverty line. Adding value and preservation of the crop is important to obtain more food and higher incomes in the market. For this, post-harvest practices and operations have to be understood and existing practices improved to suit the conditions of crop preservation and food availability.

2. Post-harvest practices for potatoes

2.1 Existing post-harvest operations

There are many post-harvest practices in potato production and they depend on the end requirement. Potatoes can be used in various ways and therefore careful planning is necessary to provide for all of these.

2.2 Use of potatoes as seed and ware (for fresh consumption)

Potatoes can be kept and used as seed for the next cultivation season, or sold as seed to other farmers in the farming community. They can also be used for large commercial seed sale if there is a planned commercial operation. In many countries in the region where potatoes are cultivated under subtropical humid conditions, seed is kept from one season to another. Seed is kept for about nine months since these countries will have only one planting season.

2.2.1 Potato storage

Storage is an important post-harvest activity in seed production. Storage under specific conditions is important to prevent excessive loss of weight as a result of driage and to preserve germination quality. Prevention of diseases in storage is also important whether it be small farmer storage or commercial potato seed storage.

2.2.2 Storage systems

A majority of stores in the countries of Asia and the Pacific region are at farm level and are for short-term storage only. These have no temperature control and have to be modified to prevent spoilage. They are used mostly to offset the low prices in the market immediately after harvest and to keep the potatoes for a few months after harvest until prices increase. Most may not be organized but in some cases seed stores are planned. Cold storage is the answer to many of the storage problems and for long-term storage. However, many small farmers are unable to obtain space in cold stores and cannot afford storage space.

A famous saying is that Asia is blessed with good conditions for bad storage. This is because the harvest in most cases and for most crops coincides with inappropriate climatic conditions to keep the crop after harvest. This is a non-controllable factor. Wet weather, increasing temperatures and high humidity after harvest give ideal conditions for pests and diseases. In some cases high temperature and low humidity give rise to weight loss or driage in the stores, resulting in revenue losses. These are the most common problems of storage. In addition to this, inappropriate storage structures do not help in preventing these storage problems. Improved storage structures therefore would prevent losses. The provision of structures with better ventilation and aeration to remove respiratory heat, provide diffused lighting for seed stores, and prevent the seepage of water is necessary. So is insect and disease control (especially tuber moth in potatoes), developing a market infrastructure for moving the harvested and stored product rapidly and improved pre-storage practices such as grading, preconditioning etc.

Small farmers who depend on their own production for seed in the next season have primitive or minimally improved farm storage. Most seed storage in this case is either in farm houses or in small sheds. Some farmers improve storage conditions by providing ventilation and also using structures with diffuse light to help keep the seed potatoes. In most cases, however, the conditions are poor and result in wastage, thus reducing the total amount of potatoes left for seed to be planted in the next season.

Commercial seed storage is available in many countries, with the best cold store facilities seen in Bangladesh and India in South Asia. Cold stores are available in many of the potato growing districts. The numbers vary but in India about 60 percent of the total produce is stored in cold stores. The percentages going into seed and for normal consumption, however, vary. Bangladesh and India have associations for cold store owners.

Since the seed is kept for long periods, it is essential that the seed be conditioned beforehand by reducing field heat (especially in cold stores). Thereafter the cold store temperatures have to be maintained well at 2 to 4 °C in order that the quality of potatoes as seed is maintained. Frequent monitoring for humidity and air composition is important.

Under farm conditions, there is not much control of temperature. In most growing countries in the subtropics, ambient temperatures increase while the produce is in storage. Proper ventilation and light management is essential to keep the seed under good conditions.

2.2.3 Structural requirements for storage

Structural requirements for farm storage depend on environmental conditions. These vary in relation to the growing conditions in different countries. In countries where harsh winters are present and potatoes are grown in the summer months (for example in Ghazni, Afghanistan and in Inner Mongolia, China), farm level storage in the winter months after the summer harvest is underground. Similar underground storage is seen in the mountain areas of Pakistan. However, these structures do not store potatoes well because of water seepage arising from the winter thaw. However, for such conditions, improved design and storage construction with very little additional cost will provide better storage over the winter period before the next summer planting. Well constructed leak-proof underground stores could tolerate temperatures as low as minus 10 °C (ambient). Examples of these stores can be seen in Afghanistan. Here, potato-growing districts with very low temperatures were provided with such stores. Potatoes removed from these stores were perfect both for ware and seed.

In areas where the temperatures are higher and farm storage is the only option, ventilation is a very important factor in addition to light control for seed. Light control is not required for ware where the potato is stored in the dark, but preferably should be at low temperatures.

Evaporative cool stores have been tried in the Indo-Gangetic Plains where potato is harvested in February and March and then kept in evaporative cool stores. However, it is essential in this case that the environment is composed of high day temperatures with very low humidity. This leaves for evaporation of a water surface in the store bottom thus cooling the store at times below 10 oC from the ambient.

2.2.4 Storage of processing potatoes

In the case of potatoes that may go into processing or that may be consumed late in the storage period, conditioning needs to be done. In low temperature long-term storage, potatoes convert the starches within its tubers into sugar, a physiological factor in potatoes. These have been well documented in different potato producing countries. Conditioning of these potatoes is therefore necessary to reconvert the sugars into starch. When potatoes with high sugar contents are processed say to chips or French fries, the resulting products are dark brown or brown coloured chips or French fries. This is because of caramelization of sugars present in the raw material.

Reconditioning of the potatoes from sugar to starch is done by increasing the temperatures in storage prior to the produce going into processing. High starch and low sugars give a better coloured potato product.

Recently, sprout suppressants have been used to prevent sprout formation in stored potatoes. Potatoes then can be stored at higher temperatures thus preventing the buildup of sugars. Potatoes stored with the use of sprout suppressants could be used for processing since the sugar content is low and not converted to sugars from starch. Commercially available formulations are available. Energy is also saved by storing the potatoes at higher temperatures, thus reducing energy that is required to cool the store.

2.2.5 Better storage practices for potatoes used for seed, ware and processing

Better storage of the harvested potatoes can be achieved by:

  1. good crop management prior to harvest;
  2. seed and ware potato drying, cleaning and preparation for storage;
  3. seed and ware grading for maturity, quality and seed size;
  4. preconditioning in the atmosphere (shade) to reduce field heat after harvest;
  5. maintenance of set temperatures in cold stores (when under cold storage);
  6. better storage structure for farm level short-term storage;
  7. maintenance of humidity to prevent driage under high temperatures and low humidity as seen in storage in the Indo-Gangetic Plains after the winter /spring harvest;
  8. better hygienic practices during storage;
  9. use of sprout suppressants for higher temperature storage (8 to 15 °C); and
  10. proper insect control, especially potato tuber moth.

2.3  Marketing as a  post-harvest activity to move the harvested and stored product

Although not considered in most discussions in the post-harvest chain, good and efficient marketing channels are important means of moving the harvested potato as fast as possible after harvest and also during storage. This reduces the time the product spends in storage before it is consumed or processed. In the vast majority of Asia and the Pacific region countries, potato markets are not well established. The advantage of a good marketing system, whether it be for seed, fresh consumption or potatoes to be processed, is that a good market chain allows the product to flow from excess areas to deficit areas in a short time. This reduces the burden on infrastructure such as storage and also lowers handling requirements. Marketing, therefore, should be considered an important and an integral part of the post-harvest chain.

Marketing provides for quality grading, branding and preparation of the produce for sale. It also provides an avenue to fetch higher prices for the potatoes that have been graded, packed and prepared for sale. With the current trend leading to the supermarket culture, preparation and sale in sophisticated markets will play an important role in distributing potatoes throughout the deficit and demand areas. Developing an organized marketing chain is a priority in post-harvest handling.

2.4  Potato processing

Adding value to the potatoes is an important activity in the potato post-harvest chain and therefore needs to be considered as a very important step in providing added income for poor farmers who could either prepare the harvested produce to be marketed to processors or could undertake small-scale farm processing to add value to the potato crop. Processing helps preserve the product during times when there is a glut, reduces storage requirements, adds value to the produce in many forms such as chips, French fries, flakes, dehydrated products, potato powder and secondary products from powders and flour etc. and thereby extends the shelf life of the semi-perishable produce.

Small scale processing activities are found in many Asia and the Pacific region countries, for example home processing for chips and dehydrated potato products. In larger potato- producing countries in the region, however, multinationals and large national firms process potatoes mainly as chips and their presence is increasing. The volume, as mentioned earlier, is still small and needs to be and is expected to be increased in the years to come. Fast food is rapidly being adopted in the booming markets of Asia and the Pacific region. Potato processing is therefore bound to increase rapidly in the near future.

The quality of the processed product is variety dependent, as processing requires high dry matter, low sugar potato varieties that have to be produced in the country. In addition, the cultivation techniques should result in a produce that is of good quality to reduce processing losses and thereby production costs. In the processing plants, attention should be given to assuring the quality of raw material at all times and throughout the processing cycle. This will keep the processing machinery of the plants active throughout the year and lower production costs.

Processing should be matched with adequate storage requirements to provide the processing plant with quality potatoes in its yearly manufacturing plan. Reversal of sugar accumulation could be done for potatoes stored for long periods. This could be done by increasing temperatures in selected time periods before processing. Reversal could also be done by using sprout suppressants as mentioned earlier.

In processing, the quality of the end product is dependent on the machinery, the oil utilized (if fried) and the time for processing etc. It is important that the countries in Asia and the Pacific region strive for their own varieties. Now, many countries depend on existing non-processing varieties for small-scale and large-scale processing. This will not yield the best quality of potatoes. India, now, has three processing varieties that are being used.

3.  Conclusions and suggestions

Post-harvest issues are many and important considering the increasing importance of potatoes in Asia and the Pacific region.

3.1  Storage

i.    Storage is important both for seed and ware potatoes as it helps reduce waste and prevents driage and processing losses if handled correctly. Good storage is required for seed, ware and processing varieties to maximize food availability and markets.

ii.   The construction of stores should be made to suit the agroclimates of the growing areas and farming conditions whether on small or large farms.

iii.  Good quality raw material should be used for storage, thereby indicating the importance of cleaning and grading of the produce prior to storage.

iv. Good store management is essential whether it is for small country stores or for large cold stores, keeping in mind the storage requirements and factors involved in management.

3.2  Processing

i)    Processing is important because it adds value to the existing potato crop and helps in increasing farm income whether the crop is sold for processing or for small-scale farm or large-scale processing.

ii)   Processing systems help in handling the excess potato crop after the harvest. Planning of processing systems to handle the excess from fresh consumption is important.

iii)  Processing varieties should be developed if the full benefits of processing are to be obtained.

iv)   Domestic processing should be encouraged to handle excess production and keep prices uniform.

v)    Special products should be developed for the emerging markets.

3.3  Marketing

i)    Marketing should be an integral part of post-harvest activities in potato production.

ii)   Marketing and market surveys should help determine the seasonal storage requirements for potatoes in a growing area.

iii)  Branding of products for the market whether for seed, ware or processed products will help develop identities in the market and develop products, thereby helping to increase farm incomes.

iv)   Developing a marketing chain when planning post-harvest activities is essential.

* Consultant, International Potato Center (CIP), South, West and Central Asia (SWCA) Regional Office and former Regional Leader, CIP-SWCA Regional Office, New Delhi 110012, India.

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