India is the largest producer of fruits and second largest producer of vegetables in the world. In spite of that per capita availability of fruits and vegetables is quite low because of postharvest losses which are perceived to be about 25 per cent to 30 per cent of production even though CIPHET study has reported much lower values. Besides, quality of a sizable quantity of produce also deteriorates by the time it reaches the consumer. This is mainly because of perishable nature of the produce which requires a cold chain arrangement to maintain the quality and extend the shelf life if consumption is not meant immediately after harvest. In the absence of a cold storage and related cold chain
facilities, the farmers are being forced to sell their produce immediately after harvest which results in glut situations and lowprice realisation. Sometime farmers do not even get their harvesting and transportation costs what to talk of the cost of production or profit. As a result, our production is not getting stabilised and the farmers after burning their fingers in one crop switch over to another crop in the subsequent year and the vicious cycle continues. A cold chain facility accessible to them will go a long way in removing the risk of distress sale to ensure better returns.
Status of Cold storage and its Potential in India
The estimated annual production of fruits and vegetables in the country has been estimated to be about 295.2 million tonnes (fruits 120.2 million tonnes & vegetables 175 million tonnes) during 2016-17 in comparison to total food grain production of 273.38 million tonnes. Because of imperfect coordination between supply and demand, seasonality and perishable nature of horticulture crops, storage plays an important role in the marketing. A chain of cold storages is set up in different states of our country. The State of Uttar Pradesh (2285) is having highest number of cold storage followed by Gujarat (753) and Punjab (655). Although, there is a vast scope for increasing the production, the lack of cold storage and cold chain facilities is one of the major bottlenecks in tapping the potential. The cold storage facilities now available are mostly for a single commodity like potato, apple, grapes, pomegranates, flowers, etc. which results in poor capacity utilisation. Almost 75 per cent of the total capacity is used for storing only potatoes, on a rental business model – where the farmers own the produce. A high dynamic business model coupled with use of refined knowledge based cold chain backed by expert business administrative skills is needed for highly perishable horticultural produce handling.
If the consumption level shoots up from the current 100 gm of fruit and 200 gm of vegetables per capita per day to at least the recommended dietary level of 140 gm and 270 gm respectively, the domestic market for fresh fruits and vegetables could be quite large and lucrative. Availability of timely robust postharvest infrastructure along with marketing system in this sector will certainly improve the socio-economic conditions of Indian citizens by providing self-reliance besides environmental protection. The vast opportunities for investment in fruits and vegetable processing units exist. It is established that fresh agri-produce loss reduction is cheaper than equivalent increase in production so far as economy, energy and impact on environment is concerned. Theoretically, one per cent post-harvest loss reduction of horticulture produce is expected to save Rs 230 crore annually.
Causes of Post-Harvest Losses: Physiological and Biochemical Aspects
The quality of the harvested fruits and vegetables depend on the condition of growth as well as physiological and biochemical changes they undergo after harvest. Fruits and vegetable cells are still alive after harvest and continue their physiological activity. The post-harvest quality and storage life of fruits appear to be controlled by the maturity. If the fruits are harvested at a proper stage of maturity the quality of the fruits is excellent. Poor quality and uneven ripening are due to early harvesting and late harvesting which results in extremely poor shelf life.
Respiration plays a very significant role in the post-harvest life of the fruits. In most of the fruits, the rate of respiration increases rapidly with ripening. The sudden upsurge in respiration is called the ‘climacteric rise’, which is considered to be the turning point in the life of the fruit. After this deterioration of the fruit begin. The fruits such as banana, papaya, mango, guava, jackfruit etc. belong to the category of climacteric fruits. While litchi, pineapple, grapes, pomegranate, lemon, orange, lime, etc. belong to the non-climacteric group. To extend the post-harvest life of the fruits its respiration rate should be reduced as far as possible. Thus, an understanding of the factors, which influence the rate of respiration, is indispensable to post-harvest technologies for manipulating the storage behaviour of fruits.
Poor handling, unsuitable containers, improper packaging and transportation can easily cause bruising, cutting, breaking, impact wounding and other forms of injury.
High post-harvest losses are caused by the invasion of fungi, bacteria, insects and other organisms. Microorganisms attack fresh produce easily and spread quickly, because the produce does not have much of a natural defence mechanism and has plenty of nutrients and moisture to support microbial growth. Post-harvest decay control is becoming a more difficult task, because the number of pesticides available is falling rapidly as consumer concern for food safety increases.
Sites of Losses
Losses may occur anywhere from the point where the food has been harvested or gathered up to the point of consumption. For the sake of convenience, the losses can be broken down into the following sub-headings:
Harvest: The separation of the commodity from the plant. In the case of roots, tubers and bulbs the commodity is lifted out of the soil.
Preparation: The preliminary separation or extraction of the edible from the non-edible portion, e.g., the peeling of fruits and vegetables.
Preservation is the prevention of lose and spoilage of foods. For example, the sun drying of fruit, the use of refrigeration and the use of fungicides to inhibit mold growth in fruits.
Processing is the conversion of edible food into another form more acceptable or more convenient to the consumer, for example, the manufacture of fruit juice and the canning of fruits and vegetables.
Storage is the holding of foods until consumption. Most storage is common storage (ambient temperature) but there are extensive storage capacities that can hold food under refrigerated or controlled atmosphere conditions.
All forms of transportation are used to transport food from the point of production to the ultimate point of consumption.
To summarise, transport losses are due to the following reasons:
Unsuitable transport containers;
Overloading of mixed fruits and vegetables (in some developing countries people and even animals ride on top of the load);
Lack of feeder roads loading to highways or collection centres;
Heat accumulation or very poor ventilation within the transport vehicles;
Virtual absence of refrigerated and insulated trucks;
Delays in product procurement after harvesting or at collection centres.
Precooling Good temperature management is the most effective way to reduce post-harvest losses and preserve the quality of fruits and vegetables. Products harvested from hot fields often carry field heat and have high rates of respiration. Rapid removal of field heat by precooling is so effective in quality preservation that this procedure is widely used for highly perishable fruits and vegetables. Currently, used precooling methods include room cooling, forced-air cooling, water cooling, vacuum cooling and package icing.
Forced-air cooling is a more rapid way of using air to cool produce. Cold air is forced to flow through the inside of each container, so that it carries away heat directly from the surface of the produce rather than from the surface of the container. The airflow is produced by creating a pressure difference between the two perforated sides of each container. The containers are stacked inside a covered tunnel with an exhaust fan at one end. Highly perishable and high-value products such as grapes, strawberries and raspberries may be cooled in less than an hour using this method.
Hydro cooling is a rapid and less expensive method. Produce is exposed to cold water by means of showering or dipping. The required cooling time is often a matter of minutes. However, not all kinds of products tolerate hydro cooling. Hydro cooled products inevitably have a wet surface, which may encourage decay in some kinds of produce.
Sanitation is of great concern to produce handlers, not only to protect produce against post-harvest diseases, but also to protect consumers from food borne illnesses. E.coli 157:H7, Salmonella, Chryptosporidium, Hepatitis and Cyclospera are among the diseasecausing organisms that have been transferred via fresh fruits and vegetables. Use of a disinfectant in wash water can help to prevent both post-harvest diseases and food borne illnesses.
Chlorine in the form of a sodium hypochlorite solution or as a dry powdered calcium hypochlorite can be used in hydro-cooling or wash water as a disinfectant. For the majority of vegetables, chlorine in wash water should be maintained in the range of 75-150 pm (parts per million). The antimicrobial form, hypochlorous acid, is mostly available in water with a neutral pH (6.5 to 7.5). Organic growers must use chlorine with caution, as it is classified as a restricted material.
Ozonation is another technology that can be used to sanitise produce. A naturally occurring molecule, ozone is a powerful disinfectant. Fruit and vegetable growers have begun using it in dump tanks as well, where it can be thousands of times more effective than chlorine.
Ozone not only kills whatever food borne pathogens might be present, it also destroys microbes responsible for spoilage. A basic system consists of an ozone generator, a monitor to gauge and adjust the levels of ozone being produced and a device to dissolve the ozone gas into the water.
Hydrogen peroxide can also be used as a disinfectant. Concentrations of 0.5 per cent or less are effective for inhibiting development of post-harvest decay caused by a number of fungi. Hydrogen peroxide has a low toxicity rating and is generally recognised as having little potential for environmental damage.
Presizing and Storage
For many commodities fruits below a certain size are eliminated manually or mechanically by presizing belt. Undersized fruits are diverted for processing. The sorting process eliminates cull, overripe, misshapen and otherwise defective fruit and separates produce by colour, maturity and ripeness classes.
Essentially all fruits and vegetables sold in modern markets are graded and sized into two or more grades according to trade standards. Sophisticated marketing systems require precise grading standards for each kind of product. More primitive markets may not use written grade standards, but the products are sorted and sized to some extent.
Typical grading facilities in large packhouses include dumpers and conveyors. Produce is graded by human eyes and hands while moving along conveyor belts or rollers. ‘Electric eyes’ are sometimes used to sort produce by colour. In small scale packing operations, one or a few grading tables may be enough. Dumping, conveying and grasping can cause mechanical injury to some products. Equipment should have a smooth, soft surface and dumping and grading operations should be gentle to minimise injuries.
Many products are sized according to their weight. Automated weight sizers of various capacities are used in packhouses. Round or nearly round fruits are often sized according to their diameter, using automated chain or roller sizers or hand carried ring sizers. An inefficient sizing operation can also cause significant injuries.
Food grade waxes are commonly applied to replace some of the natural waxes removed in the washing and cleaning operations to reduce water loss and to improve appearance. It also provides protection against decay organisms. Waxing may be done after grading and fungicides may be added to the wax. Application of wax and postharvest fungicides must be indicated on each container where the refrigerated storage facilities are not available Protective skin coating with wax is one of the methods for increasing the storage life of fresh fruits.
Packaging of fresh fruits and vegetables has a great significance in reducing the wastage. Packaging provides protection from physical damage during storage, transportation and marketing. There are variety of packages, packaging materials and inserts available. There are two types of packaging. The first is when produce is packed in containers for transportation and wholesale. The second is when produce is packed into small retail units. Ideal containers for packing fruits and vegetables should have the following attributes. They are easy to handle, they provide good protection from mechanical damage, they have adequate ventilation and they are convenient for merchandising. They should also be inexpensive and easily degradable or recyclable. Many kinds of containers have been used but the ‘ideal’ is yet to be found. Users often put economic considerations first is selecting containers. Fancy containers such as fiber board boxes or wooden or plastic crates are often used for high-value products. Inexpensive containers such as bamboo baskets or nylon net sacs are used for low-priced produce. Methods of packaging can affect the stability of products in the container during shipping and influence how much the container protects their quality. In fiber board boxes, for example, delicate and high-priced products are often packed in trays, while other products are simply put in the box in groups.
Prepackaging or consumer packaging generally provides additional protection for the products. It is also convenient for retailers as well as customers, and therefore adds value to produce. However, over-use of non-biodegradable plastic trays and wrapping materials, as often seen in modern supermarkets, which creates an extra burden of waste disposal and damages the environment.
Factors Affecting Storage Life
Transpiration rates (water loss from produce) are determined by the moisture content of the air, which is usually expressed as relative humidity. At high relative humidity, produce maintains salable weight, appearance, nutritional quality and flavour, while wilting, softening and juiciness are reduced. Leafy vegetables with high surface-to-volume ratios; injured produce and immature fruits and vegetables have higher transpiration rates. High temperatures, low relative humidity and high air velocity increase transpiration rates.
Relative humidity needs to be monitored and controlled in storage. Control can be achieved by a variety of methods:
Operating a humidifier in the storage area.
Regulating air movement and ventilation in relation to storage room load.
Maintaining refrigeration coil temperature within the storage room.
Using moisture barriers in the insulation of the storage room or transport vehicle.
Wetting the storage room floor.
Using crushed ice to pack produce for shipment.
Sprinkling leafy vegetables, coolseason root vegetables and immature fruits and vegetables with water.
Respiration and metabolic rates are directly related to room temperatures within a given range. The higher the rate of respiration, the faster the produce deteriorates. Lower temperatures reduce respiration rates and the ripening and senescence processes, which prolong the storage life of fruits and vegetables. Low temperatures also slow the growth of pathogenic fungi, which cause spoilage of fruits and vegetables in storage.
Producers should give special care and attention to proper storage conditions for produce with high to extremely high respiration rates, as these crops will deteriorate much more quickly.
It is impossible to make a single recommendation for cool storage of all fruits and vegetables. Climate of the area where the crop originated, the plant part, the season of harvest and crop maturity at harvest are important factors in determining the optimum temperature. A general rule for vegetables is that coolseason crops should be stored at cooler temperatures (0 to 1.7oC) and warmseason crops should be stored at warmer temperatures (7 to 13oC).
Temperatures that are too low can be just as damaging as those too high. Freezing will occur in all commodities below 0oC. Whether injury occurs depends on the commodity. Some can be repeatedly frozen and thawed without damage, while others are ruined by one freezing.
Injury from freezing temperatures can appear in plant tissues as loss of rigidity, softening and water soaking. Injury can be reduced if the produce is allowed to warm up slowly to optimum storage temperatures and if it is not handled during the thawing period. Injured produce should be marketed immediately, as freezing shortens its storage life.
Fruits and vegetables that require warmer storage temperatures (4.5 to 13oC) can be damaged if they are subjected to near-freezing temperatures (0oC). Cooler temperatures interfere with normal metabolic processes. Injury symptoms are varied and often do not develop until the produce has been returned to warmer temperatures for several days. Besides physical damage, chilled produce is often more susceptible to disease infection.
Ethylene, a natural hormone produced by some fruits as they ripen, promotes additional ripening of produce exposed to it. The old age saying that one bad apple spoils the whole bushel is true. The damaged or diseased fruits produce high levels of ethylene and stimulate the other apples to ripen too quickly. As the fruits ripen, they become more susceptible to disease. Ethylene producers should not be stored with fruits, vegetables, or flowers that are sensitive to it. The result could be loss of quality, reduced shelf life and specific symptoms of injury. Ethylene producers include apples, apricots, avocados, ripening bananas, honeydew melons, papayas, peaches, pears, plums and tomatoes.
Crops that require different storage conditions will need three different storage facilities.
Cold Storage (temperatures 0 to 2.2°C)
Cool Storage (temperatures 4.5 to 13°C)
Warmer storage (temperatures 13 to 20°C)
A recording thermometer can be helpful in determining whether storage facilities are maintaining ideal conditions and are not fluctuating. A maximum or minimum thermometer could be substituted. Relative humidity also should be monitored with a hygrometer.
Controlling and monitoring temperature and relative humidity will enable a grower to maintain optimum storage conditions for maximum storage life of the crop and to minimize crop damage from chilling, freezing or high temperature injuries and water loss from the crop.