storage & processing of vegetable, post harvest, transport


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Vegetable storage and Processing:

Vegetable storage and Processing


Storage The management of temperature and relative humidity are the most important factors determining storage life of vegetable crops. The natural means like ice, water, night temperature have been used for long time for protecting food materials from spoilage and these are still common. However, with the development of innovative technologies, it is possible to achieve optimal environments in the insulated stores. In India onion, garlic and potato are important vegetables which need long period of storage in large quantity.

Goals of storage:

Goals of storage To meet the demand of fresh vegetables throughout the year. To reduce waste during glut season and to avoid the low price during peak season. To extend the processing season of some commodities. To provide planting material when needed. To slow biological activity of product by maintaining the lowest temperature. To slow growth and spread of microorganisms. To reduce product moisture loss.

Storage: general facts:

Storage: general facts If produce is to be stored, it is important to begin with high quality produce. The lot of produce should not contain damaged or diseased units, and containers must be well ventilated and strong enough to withstand stacking. Damaged produce will lose water and have higher decay rates in storage as compared to undamaged produce. In general, proper storage practices include temperature and relative humidity control, air circulation and maintenance of space between containers for adequate ventilation and avoiding incompatible produce mixtures.

Factors affecting storage:

Factors affecting storage Temperature Relative humidity Atmospheric composition Light

Effects of Temperature:

Effects of Temperature Temperature is the most important factor that influence rate of deterioration of harmful commodities. For each increase of 10 0 C above optimum, rate of deterioration increases by two to three fold. Rate of enzymatic reactions involve in the process of respiration within physiological temperature range, increases exponentially with increase in temperature. Temperature below optimum range causes physiological disorders like freezing and chilling injury.

Effects of Relative humidity:

Effects of Relative humidity An effective method for reducing water loss from vegetables is to increase relative humidity of air. The relative humidity in a storage facility should be kept in the range of 90 to 95 %. Humidity below this range results in unacceptable moisture loss. Humidity close to 100% may also cause excessive growth of microorganisms and may also cause cracking.

Effects of Atmospheric composition:

Effects of Atmospheric composition Storage life of vegetables are mostly affected by concentration of CO 2 and O 2 in surrounding environment. Shelf life of these perishables can be enhanced by maintaining an atmosphere, in which O 2 content is low and CO 2 concentration is more than in normal air.

Effects of Light:

Effects of Light Influence of light has not been adequately studied; however it may affect final atmosphere of packed fresh produce. In presence of light photosynthetic green vegetables could counteract the process of respiration by utilizing CO 2 and producing O 2 . Some commodities are adversely affected by excessive light, viz. The chlorophyll bleaching of Brussels sprout. Exposure of potatoes in light also results in greening due to formation of chlorophyll.

Storage temperature and relative humidity:

Storage temperature and relative humidity Cooling Method(s) Temp. o F Freezing Temp o F Relative Humidity % Storage Life Tomatoes R,F 46-50 31 90-95 1 week Okra R,F 45-50 29 90-95 7-10 days Beans R,F,H 40-45 31 95 7-10 days Brinjal R,F 45-54 31 90-95 1 week Garden Peas F,H 32 31 95-98 1-2 weeks Chilli R,F 45-50 31 90-95 2-3 weeks Squash melon R,F 45-50 31 95 1-2 weeks Watermelon R 50-60 31 90 2-3 weeks Musk melon H 32-40 30 95 2 weeks Cucumber F,H 45-50 31 95 2 weeks R: refrigerated; F: freezing; H: hydrobaric ;

Storage systems:

Storage systems

Storage systems:

Storage systems Refrigerated / low temperature storage Controlled atmosphere storage Evaporative cool storage Evaporative cool storage (Zero energy) Hypobaric or Low Pressure Storage (LP)

Refrigerated / low temperature storage:

Refrigerated / low temperature storage The temperature in storage facility normally should be kept within 1 0 C of the desired temperature for the commodities being stored. Temperature below the optimum range for commodity cause freezing or chilling injury and temperature above it, shorten storage life. It is important to precisely control temperature and relative humidity conditions inside the refrigerated storage environment.

Controlled atmosphere storage (CA):

Controlled atmosphere storage (CA ) It is based, on the principle of maintaining an artificial atmosphere in storage room, which has higher concentration of CO 2 and lower concentration of O 2 than normal atmosphere. This reduces the rate of respiration and thus delays aging. This method of storage is very effective when combined with low temperature storage.

Evaporative cool storage (Zero energy):

Evaporative cool storage (Zero energy) Evaporative cooler is located on the peak of a storage structure which can cool can entire room stored produce such as sweet potato and other chilling sensitive crops. The vents for outside air should be located at base so that cool air is circulated throughout the room before exit. The entire building is set below the ground level taking advantage of the cooling properties of soil.

Hypobaric or Low Pressure Storage (LP):

Hypobaric or Low Pressure Storage (LP) It is the form of controlled atmospheric storage in which the produce is stored in partial vacuum. It is the effective method for reducing oxygen and for accelerating the escape of ethylene and other volatiles. Ripening of vegetables is retarded by hypobaric storage, due to reduction in partial pressure of oxygen up to concentration of 2 percent at normal atmospheric pressure

Alternative storage:

Alternative storage In-situ storage Storage in sand Pit storage Field storage in heaps

In-situ storage:

In-situ storage In-situ storage means delaying the harvest of the crop until it is required. This can be practised in crops like cassava and potato. Storage of potatoes for upto 3 months can be practised in Meghalaya and Kumaon hills. The disadvantage is that the crop can be exposed to pests and diseases attack and land remain occupied.

Storage in sand:

Storage in sand This method is practised for storage of small quantity of potato on layer of sand on Katcha floor in houses. This method is used in Bihar for storage of potatoes upto six months.

Pit storage:

Pit storage Pit is another traditional method of on-farm storage. In Himachal Pradesh, farmers make Katcha pits( 4x4x4 ft) or Pakka pits and store cabbage, cauliflower, peas and beans for 1-3 months during winter.

Field storage in heaps:

Field storage in heaps This is widely used in field to store vegetables in heaps. For eg : Potato, onions, pumpkin, sweet potato etc are stored in heaps in field and covered with straw and dried sugarcane leaves. The temperature inside the heap is 10 to 14 0 C lower and RH 18-20% higher than the ambient. This method ensures that produce is free from soil humidity and is protected from weather. It is also cost effective for bulky crops that require large buildings for storage.

Processing of vegetables:

Processing of vegetables

Processing of vegetables:

Processing of vegetables Because of the variation in growing and harvesting seasons of different vegetables at different locations, the availability of fresh vegetables differs greatly in different parts of the world. Processing can transform vegetables from perishable produce into stable foods with long shelf lives and thereby aid in the global transportation and distribution of many varieties of vegetables.

Goal of processing:

Goal of processing The goal of processing is to deter microbial spoilage and natural physiological deterioration of the plant cells.

Techniques in vegetable processing:

Techniques in vegetable processing Blanching Dehydration Canning Freezing Fermentation and pickling Irradiation


Blanching Vegetables have been washed clean, they must undergo blanching (heating) in hot water at 88° C (190° F) for two to five minutes or with steam in a conveyor at 100° C (212° F) for one-half to one minute. Blanching inactivates natural enzymes that would cause discoloration and off-flavours and aromas. It also serves to reduce the number of microorganisms and to render vegetables limp for easy packing into containers.

Blanching (cont.):

Blanching (cont.) For some vegetables, such as spinach, snap beans, and collards, the blanching step also serves to remove harsh flavours. After blanching the vegetables must go through rapid cooling in either cold water or cold air for better quality retention. The vegetables are then ready for the various food-processing methods .


Dehydration Drying is probably the oldest method of preserving foods. The removal of water from vegetables is accomplished primarily by applying heat, whether it be through the radiant energy of the sun or through air heated by electrical energy. A major advantage of removing water is a reduction in volume and weight, which aids in storage and transportation of the dried products. Modern drying techniques are very sophisticated. Many machines are available to perform tunnel drying, vacuum drying, drum drying, spray drying, and freeze-drying.

Dehydration (cont.):

Dehydration (cont.) Although freeze-drying produces a food of outstanding quality, the cost is high, and it has not been used widely in vegetable products. A small amount of sulfite may be used in producing certain dried vegetables. The sulfite serves as an antimicrobial agent, aids in heat transfer, and (in the case of potatoes) acts as a blanching agent. A small percentage of the consumer population is allergic to sulfite . Although the rehydrated product contains little or no sulfite


Canning Method of preserving food from spoilage by storing it in containers that are hermetically sealed and then sterilized by heat. Or Putting foods into metal cans or glass jars is the major food-processing method of the world. It is particularly useful in developing countries where refrigeration is limited or nonexistent. In the canning process, vegetables are often cut into pieces, packed in cans, and put through severe heat treatment to ensure the destruction of bacteria spores.

Canning (cont.):

Canning (cont.) The containers are sealed while hot so as to create a vacuum inside when they are cooled to room temperature. Properly processed canned vegetables can be stored at room temperature for years. Minor defects of the process : Bulges occur in cans after a long storage time. For safety reasons, the contents of these cans should not be consumed. Although in most cases bulged cans are caused by the formation of gas from chemical reactions between the metal cans and their acidic contents, there is a remote possibility that inadequate heat processing did not destroy all bacteria spores.


Freezing It is the method of preserving food by lowering the temperature to inhibit microorganism growth. Frozen foods have outstanding quality and nutritive value. Indeed, some frozen vegetables, such as green peas and sweet corn, may be superior in flavour to fresh produce. The high quality of frozen foods is mainly due to the development of a technology known as the individually quick-frozen (IQF) method. IQF is a method that does not allow large ice crystals to form in vegetable cells. Most commercial freezing is done either in cold air kept in motion by fans (blast freezing) or by placing the foodstuffs in packages or metal trays on refrigerated surfaces (contact freezing).

Fermentation and pickling:

Fermentation and pickling In both fermented and pickled vegetables, acid is used to preserve the products. Pickled vegetables include cucumbers, green tomatoes, onions, radishes, and cabbages. The variety of vegetables used for fermentation or pickling may not be the same as fresh market vegetables. Owing to the acidic environment, fermented or pickled vegetables need less heat treatment before being placed in containers.


Irradiation Ionizing radiation, mostly gamma-ray, has been used in several countries to preserve vegetables. The practice is quite common in preventing potatoes from sprouting during long-term storage. Despite studies showing that products treated with low-dose ionizing radiation are safe, consumers are still concerned about this processing technology and have not accepted it.

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