In this article we will discuss about:- 1. Introduction to Post-Harvest Management 2. On-Farm Storage of Vegetables 3. Packing and Pre-Cooling 4. Control Atmosphere/Modified Atmosphere 5. Establishment of Cold/Cool Chain 6. Marketing 7. Conclusion.
Introduction to Post-Harvest Management:
Unlike other horticultural rich countries, Indians are not getting their basic daily requirement of vegetables. In India there are many lacunas in the existing post-harvest handling, storage and transportation of vegetables. In addition to the high rate of population growth there is a heavy post-harvest loss.
Furthermore, only a small fraction of vegetables is utilized for processing and export. Therefore, the loss rate has to be gradually cut down in order to achieve the target of surplus vegetables for industry and export after meeting the nutritional requirement of the country.
In the developed countries most of the vegetables are selected, placed in bulk containers and transported to packing station. They are placed temporarily in cool storage for subsequent loading or loaded directly into transport vehicles, preferably refrigerated, and transported to market.
Various important operations are also carried out at packing stations. Perishable horticultural produce in our country is marketed immediately after harvesting without primary processing as a result of which large amount of inedible parts are also transported for marketing which ends up as garbage.
There are various advantages, for primary processing, such as:
(a) Reduction of bulk,
(b) Longer shelf-life,
(c) Less transportation cost,
(d) Convenient food, and
(e) Employment generation.
On-Farm Storage of Vegetables:
In a tropical country like India tremendous amount of quality deterioration takes place immediately after harvest due to lack of on-farm storage facilities. The low cost environment friendly zero energy cool chambers which work on the principle of evaporative cooling using locally available materials like bricks, sand, bamboo etc., can be used to overcome this problem.
The small cool chambers can be utilized in the farm home to store fresh fruits and vegetables so that better nutrition may be obtained. Small and marginal farmers may use it to store a few days harvest. The big chambers of commercial size are useful for the storage of vegetables and during the rainy season onion can be stored if water supply is stopped in the big cool chamber. The temperature in these chambers is not expected to rise beyond 15°C even when the day field temperature may rise to 30°C resulting in softening of the vegetable.
Thus the cool chamber is expected to maintain the texture of the vegetable which is of prime importance in marketing of these commodities. Evaporative cooling is accomplished by misting or wetting the produce in the presence of a stream of dry air. It works best when the relative humidity of the air is below 65 %. At best, however, it reduces the temperature of the product only 5° to 7° C and does not provide consistent and thorough cooling. It is an inexpensive way of cooling.
Packing and Pre-Cooling of Vegetables:
Traditionally, vegetables are packed in gunny bags, wooden boxes and bamboo baskets. Ventilated Corrugated Fibre Board (CFB) boxes are also used in export of vegetables. Wrapping vegetables in HM film delays senescence and increases the shelf-life during transportation. Similarly, film wrapping coupled with ethylene absorbent extends the shelf-life, by reducing the physiological and biochemical changes.
The precooling technology is extensively used in developed countries in the post-harvest handling of vegetables. The environment friendly low cost evaporative cool chamber developed can be gainfully used for pre-cooling of vegetables.
There are several types of cooling procedures that can be used after harvesting of vegetables. These differ in their rate and effectiveness of cooling, compatibility with specific commodities and cost.
Vegetables packed in bins are transported to a refrigerated room. Rapidity of cooling is dependent on the flow of cooled air around the bins. Proper stacking of the bins is important for effective cooling. Room cooling may be used with most commodities but may not be highly effective for those that require quick cooling.
It is effective for storing precooled produce but in some cases it cannot remove field heat rapidly enough. For bins of produce, room cooling is often inefficient because the density of the packed vegetables allows for little surface contact with the cooled air. Dehydration can also be a problem because of the constant airflow over the surface of the vegetables. Properly designed, room cooling system can be relatively energy efficient.
Forced air cooling is similar to room cooling except that the bins are vented and stacked. Cooled air is forced by a pressure gradient through the bins, allowing better contact of cool air with warm product. Pressure gradients are created by fans that draw air around and through the bins. Forced air cooling is faster than room cooling.
Although the cooling rate depends on air temperature and the rate of air flow through the packages, forced air cooling is usually 75 to 90 % faster than room cooling. Once the product is cooled, the forced air can be stopped and the product can be kept under refrigeration with little air movement and water loss. Forced air cooling can be very energy efficient and is an effective way to increase the heat removal rate of a cooling room.
Hydro cooling is achieved by flowing chilled water over the product, rapidly removing the heat. At typical flow rates and temperature differences, water removes heat about 15 times faster than air. Hydro cooling can be used on most commodities that are not sensitive to wetting. It is generally not recommended for leafy vegetables because excessive free moisture can encourage diseases.
Vacuum cooling is the best method for cooling vegetables that have a high ratio of surface area to volume, such as the leafy vegetables. Air is pumped out of the chamber containing the product. The vacuum causes water to evaporate from the surface of the produce. As water leaves the product due to reduced air pressure, it carries heat with it.
Cooling is very rapid. Vacuum coolers can be energy efficient but are expensive to purchase and operate. Some vacuum coolers are portable and can be used in more than one location. This is especially cost effective when the harvest moves from one location to another with the change of season.
For each 6° C of cooling, about 1% water is lost form the product. Some vacuum coolers add a fine spray of water to reduce water loss. Water loss from vacuum cooling of lettuce is only 0.5 to 1.5 % and is usually not considered a problem for the product. After cooling, the vegetable is moved to a cold room or refrigerated truck.
In top icing, crushed ice is added over the top of selected produce by hand or machine. For liquid icing, a slurry of water and ice is injected into the produce packages through vents or handholds without removing the package tops. Icing is very effective on dense packages that cannot be cooled with forced air and can be used on a variety of vegetables. Because ice has a residual effect, this method works best with vegetables that have a high respiration rate, such as broccoli and sweet corn. One kilogram of ice will cool about 6 kilogram of produce from 30° C down to 10° C.
Loading and unloading are very important steps in the post-harvest handling of fruits and vegetables but are often neglected One of the problems in our country is the non-introduction of pallets in the trading of fruits and vegetables. With the introduction of CFB boxes, the post-harvest loss can be considerably reduced by using pallets.
All the subsequent handling operations become very easy once the boxes are placed on the pallets. It is also essential to introduce mechanical loading and unloading particularly with the use of fork-lift trucks while handling pallets.
Though containers have been introduced recently in our country in a big way, these are not at present used for carrying fresh horticultural produce for internal distribution. In the advanced countries, refrigerated containers are available for shipment of fruits, vegetables and flowers. Low cost refrigerated containers can be designed and fabricated to suit our requirements by introducing ventilation and evaporative cooling.
One of the greatest advantages of the container is that it can be placed on truck or rail. Palletisation and containerization will go a long way in establishing both internal and international trade on a firm footing.
viii. Cool Store:
The ideal condition for fresh vegetables is the lowest temperature which does not cause chilling injury to the product. In India, the first cool store was established in Calcutta in 1892. At present there are 2,970 cold storages with an installed capacity of 77, 87,599 tonnes. Electricity is the most important input for cool stores but unfortunately it is not available freely and abundantly in India.
Control Atmosphere/Modified Atmosphere of Vegetables:
The main purpose of controlled atmosphere (CA) or modified atmosphere (MA) is to adjust the atmospheric composition surrounding the commodity by removal (mainly O2) or addition (mainly CO2) of gases at a concentration that is different from the atmosphere. The first requirement for controlled atmosphere is a sufficiently gas tight chamber and the second is some means for maintaining the concentration of CO2 and O2 at the desired level. This method in combination with refrigeration markedly enhances the storage life of vegetables.
Establishment of Cold/Cool Chain for Vegetables:
One of the important reasons for advancement in the trade of vegetables in the developed countries is the adoption of cold chain in handling of vegetables. The maintenance of low temperature during transit and at different stages of the handling process can reduce the losses and can retain the quality of vegetables and their products.
It may not be possible to introduce the cold chain facility in our country in the pattern of developed countries immediately, owing to several difficulties such as high cost, lack of abundant uninterrupted power supply etc. In this respect the advantages of the evaporative cooling can be utilized and a cool chain based on the principle of evaporative cooling can be established in our country.
Marketing of Vegetables:
In India it is often found that there is glut of a particular vegetable in one part of the country when it is scarce in the other part. Due to improper post-harvest management and lack of adequate processing facilities a huge quantity of fruits and vegetables are lost in our country.
This can be checked if they are processed into value added products or adequately distributed in different parts of the country. There is a great scope of domestic trade in our country by improving the post-harvest distribution facility of these highly perishable commodities.
If the vegetables are evenly marketed from the place of abundance to the place of scarcity not only the consumers get the produce at a reasonable price but the producer will also get attractive prices. It is unfortunate that the unscrupulous traders and middlemen involved in this business do not cooperate in this matter. On the contrary they create artificial scarcity. Much organizational improvements are to be made for trading vegetables in the domestic front.
In spite of an abundant and varied production base, India’s performance in export of horticultural produce has not been encouraging. Lack of infrastructural facilities which result in heavy post-harvest losses, coupled with low productivity and high price of raw materials makes our exports uncompetitive in the international market. The Government is committed to provide a massive thrust to agro-based industries in an endeavor to enhance the earnings of farmers, create employment opportunities and diversify the rural economy.
A determined effort is to be made to improve the entire post-harvest system of handling, storage and transportation and to fulfill the developmental needs in these aspects.
In order to achieve these objectives the following points are to be considered seriously:
(a) Increase of packing station facilities including pre cooling systems,
(b) Introduction of palletisation and containerization,
(c) Proper temperature management during storage with emphasis on low cost cooling system based on evaporative cooling, and
(d) Fast transportation and establishment of cold/cool chain. It is necessary to mention that post-harvest management is an integrated process and has to be undertaken in totality.