Author: Pawan Singh Gurjar
Several pre-harvest and post-harvest factors affect the quality and shelf life of horticultural crops. Some of these factors are related to plant, others are related to environment and cultural practices.
Pre-harvest factors
A). Related to plants
Type of fruit crop: Shelf life of the fruit are varies from crop to crop e.g. jackfruit, bael, apple, pumpkin, water melon having good shelf life while mango, cherry, strawberry, peach, plum, guava, tomato, etc having less shelf life.
Cultivars: The shelf life of fruits varies according to variety within a crop. Because several parameters of shelf life are controlled genetically. Varieties with shorter shelf-lives are generally prone to higher post harvest losses. Varieties with thick peel, high firmness, low respiration rate and low ethylene
production rates would usually have longer storage life. The cultivars that have ability to withstand the rigors of marketing and distribution will have lesser losses after harvest. Varieties with resistance to low temperature disorders and/or decay-causing pathogens can be stored well for longer duration with minimum storage losses. Hence, while growing horticultural crops, one must choose such varieties that inherently have got good quality and storage potential in addition to the high yield and pest resistance potential. For example in Guava Lalit variety has less shelf life than L-49. Similarly in mango Mallika has more shelf life than Lucknow Safeda and Dashahari.
Planting density: It affects the quantity, quality and shelf life of the produce. High density planting increases competition between plants, reduces light availability, and thus may decrease quantity. Low density planting lead to large size, better colored fruit which may have shorter shelf life. Larger fruits are commonly more sensitive to physiological disorders.
B) Related to intercultural operations
Water relation and irrigation: Stress due to excessive or inadequate water in the medium reduces the longevity of the fruits. In general, <5 % of water absorbed in the plant system is utilized for the development of different plant components. Moisture stress increases the rate of transpiration over the rate of absorption and irregular irrigation/ moisture regime leads fruit cracking (pomegranate cracking). Higher level of moisture stress affects both yield and quality by decreasing cell enlargement. Crops which have higher moisture content generally have poorer storage characteristics. An example of this is the hybrid onions, which tend to give high yield of bulbs with low dry matter content but which have only a very short storage life. If fully matured banana harvested soon after rainfall or irrigation the fruit can easily split during handling operations, allowing micro organism infection and post harvest rotting. If orange is too turgid at harvest (early morning) the flavdeo/oil gland in the skin can be ruptured during harvesting, releasing phenolic compounds and causes Oleocellosis or oil spotting (green spot on the yellow / orange coloured citrus fruit after degreening).
Mango hot water treatment is better if there is delay of 48 hr. between harvest and treatment and resulted better efficiency of hot water in disease control.
Generally, crops that have higher moisture content or low dry matter content have poorer storage characteristics. Keeping quality of bulb crops like onion and garlic will be poor if irrigation is not stopped before three weeks of harvesting.
Mineral nutrition: Balanced application of all nutrient elements is necessary for the maintaining growth and development of the plants. The application of fertilizers to crops influences their post harvest respiration rate. Excess or deficiency of certain elements can affect crop quality and its post harvest life. Numerous physiological disorders are also associated with mineral deficiencies which ultimately lead to post harvest losses.
Nitrogen - High nitrogen fertilization reduces while moderate to high potassium improves post harvest life and quality of pomegranate and many horticultural produce. Application of potassium in water melon tends to decrease the post harvest respiration. High levels of nitrogen tend to decrease flavor, TSS, firmness and color of the fruit and in stone fruits (peach, plum, apricot) it increases physiological disorders and decrease fruit colour.
Generally, crops that have high levels of nitrogen typically have poorer keeping qualities than those with lower levels. As high nitrogen increases fruit respiration, faster tissue deterioration thereby reducing their storage life.
Phosphorous - Phosphorous nutrition can alter the post harvest physiology of some produce by affecting membrane lipid chemistry, membrane integrity and respiratory metabolism. The respiration rate of low-phosphorous fruits will be higher than that of high phosphorous fruits during storage.
Potassium - Potassic fertilizers improves keeping quality, its deficiency can bring about abnormal ripening of fruits and vegetables. Potassium helps in reducing some physiological storage disorders, e.g. superficial rind pitting in oranges.
Calcium - the storage potential of the fruits is largely dependent on the level of calcium and it is associated with produce texture. The higher level of nitrogen, phosphorus and magnesium and low levels of potassium and boron lead to the Ca deficiency in fruits and reduce its storage life. Reduction in calcium uptake causes lateral stem breakage of poinsettia. Calcium treatment delays ripening, senescence, reduces susceptibility to chilling injury, increase firmness and reduces decay subsequent to storage in avocados and improves the quality.
Physiological disorders of storage organs related to low Ca content of the tissue are
- Bitter pit in apples
- Cork spot in pears
- Blossom end rot in tomato
- Red blotch of lemons
The incorporation of 4% Ca into proto pectin of middle lamella form bond with the cellulose of the cell wall and thus delayed softening in fruits.
Infused Ca inhibits the internal browning, retarded respiration, and reduced the metabolism of endogenous substrates. Post climacteric respiration of apple decreased as peel Ca level increased from 400 to 1300 ppm. Calcium may reduce the endogenous substrate catabolism by limiting the diffusion of substrate from vacuole to the respiratory enzymes in the cytoplasm (limited membrane permeability). Application of CaCl2 delayed the accumulation of free sugars, decreased inorganic contents, mold development, softening and development of red colour in strawberry. In pears reduced cork spot, increased flesh firmness, total acidity and juiciness and in apple even after 90 day of storage at ambient condition shown acceptable quality.
Canopy manipulation
Fruit thinning – increases fruit size but reduces total yield. It helps in obtaining better quality produce.
Fruit position in the tree – Fruits which are exposed to high light environment possesses higher TSS, acidity, fruit size, aroma, and shelf life compared to which lies inside the canopy. Hence better training system should be practiced to circulate optimum light and air. Eg.: Grapes, Mango, peaches, kiwifruits.
Girdling - increases the fruit size and advance and synchronized fruit maturity in peach, litchi and nectarines. Increases fruitfulness in many fruit tree species.
Use of Agrochemicals: Use of chemicals on the plants to prevent the pathogen will have direct impact on extending the postharvest life. Generally, if produce has suffered an infection during development its storage or marketable life may be adversely affected. Banana which suffers a severe infection with diseases such as leaf spot may ripen pre maturely or abnormally after harvest and in mango it is rapid postharvest loss. Pre harvest application chemicals like MH on onion filed prevent them sprouting during storage.
C). Related to environment
Light: Light regulates several physiological processes like chlorophyll synthesis, phototropisum, respiration and stomatal opening. The duration, intensity and quality of light affect the quality of fruits and vegetables at harvest. Most of the produce needs high light intensity (3000-8000 f.c.). Absorption of red light (625-700 nm) through pigments, phytochrome, is essential for carbohydrates synthesis which determines the shelf life of the produce.
Citrus and mango fruits produced in full sun generally had a thinner skin, a lower weight, low juice content and lower acidity but a higher TSS. And citrus fruits grown in the shade may be less susceptible to chilling injury when subsequently stored in cold storage.
In tomatoes, leaf shading of fruits produced a deeper red colour during the ripening than in the case of those exposed to light. The side of the fruit that have been exposed to sun will generally firmer than the non exposed side. In general, the lower the light intensity the lower the ascorbic acid content of plant tissues. In leafy vegetables, leaves are larger and thinner under condition of low light intensity.
Humidity: High humidity during growing season results in thin rind and increased size in some horticultural produce and this produce is more prone to high incidence of disease during post harvest period. Humid atmosphere may cause the development of fungal and bacterial diseases, which damages produce during storage and transport. Damaged produce remove water very quickly and emit a larger concentration of ethylene than healthy ones. Low humidity may cause browning of leaf edge on plants with thin leaves or leaflets. High humidity can maintain the water – borne pollutants in a condition so that they can be more easily absorbed through the cuticles or stomata’s. Reduced transpiration leads to calcium and other elemental deficiency.
Temperature: All type of physiological and biochemical process related to plant growth and yield are influenced by the temperature. The higher temperature during field conditions decreases life and quality of the produce. At high temperature, stored carbohydrates of fruits are quickly depleted during respiration and plant respires at the faster rate. The produce which is having higher amount of stored carbohydrates show longer storage. For example- high temperature during fruiting season of tomato leads to quick ripening of fruits on and off the plant.
Orange grown in the tropics tend to have higher sugars and TSS than those grown sub tropics. However, tropical grown oranges tend to be green in colour and peel less easily and it is due to the lower diurnal temperature that occurs in the tropics.
Rainfall: Rainfall affects water supply to the plant and influences the composition of the harvested plant part. This affects its susceptibility to mechanical damage and decay during subsequent harvesting and handling operations. On the other hand, excess water supply to plants results in cracking of fruits such as cherries, plums, and tomatoes.
During harvest factors
Season: Quality of produce are greatly inf luenced by season e.g. Winter season harvest having more shelf life as compared to other season, while off season fruits and vegetables give more remunerative price. Harvesting during or immediately after rains should not be carried out since it creates most favourable conditions for multiplication of micro-organisms. Citrus fruits become susceptible to damage if harvested during rains as their rind becomes turgid and prone to easy bruising, sun-scald etc.
Time: Fruits and vegetables should always be harvested when temperature ismild. Because, higher temperature leads to faster respiration. Morning harvest of horticultural crop prefer for local market because they are fully fresh and turgid and having dew drop in this time. Evening harvesting is preferred for distant market due to higher accumulation of reserved carbohydrates and less amount of moisture which give the better quality of the produce to consumer.
Method of harvesting: Selection of suitable method for harvesting of the produce is necessary otherwise bruises or injuries during harvesting may later manifest as black or brown patches making them unattractive. Latex coming out of stem in mango should not be allowed to fall on fruits as it creates a black spot. Injury to peel may become an entry point for microorganisms, causing rotting. Some harvesting gadgets have been developed, e.g. mango harvester in Lucknow (CISH).
Stage of harvesting: Fruits must be harvested at right stage of maturity. A very common cause of poor product quality at harvest and rapid deterioration thereafter is harvesting immature fruits. Fruits harvested immature or over mature usually do not keep long. Fruits harvested too early lose water fast and are more susceptible to mechanical damage and microbial attack. An over mature fruit is more susceptible to decay, has passed its best eating quality, and deteriorates fast.
Post-harvest factors
Pre-cooling: High temperatures are detrimental to keeping quality of fruits and vegetables, especially when harvesting is done during hot days. Pre-cooling is a means of removing the field heat. It slows down the rate of respiration, minimizes susceptibility to attack of micro-organisms, and reduces water loss.
Washing and drying: Most of the fruits and vegetables are washed after harvesting to improve their appearance, to prevent wilting and to remove primary inoculum load of microorganism. Hence, a fungicide/bactericide should be used in washing water. Washing, improves shelf life of bananas by delaying their ripening. After washing, excess of water should be removed which would otherwise encourage microbial spoilage.
Sorting and grading: Fruits and vegetables require sorting and grading for uniform packing at field level. Sorting is done on the basis of size and colour while grading practice is performed as per the defect or on the basis of marketable and unmarketable produce.
Disinfection: Papaya, mango, melon and other fruits are susceptible to fruit fly attack. Disinfection is done either by vapour heat treatment (VHT) at 43°C with saturated air with water vapour for 6-8 hr by Ethylene dibromide fumigation.
Waxing: Fruits and vegetables have a natural layer on their outer surface which is partly removed by washing. An extra discontinuous layer of wax applied artificially with sufficient thickness and consistency to prevent anaerobic condition within the fruits provides necessary protection against decay organism. Waxing also improves the appearance and glossiness, making them more acceptable.
Packing: It means more than carrying multiples of an object. Packing not only protects the horticultural produce but also makes a favourable impression on the buyers and May able to fetch higher income.
Delivery: Moving the harvest produce from the farm to the customer in good condition is important. All efforts up to delivery can be invalid if the fresh fruits and vegetables reach the destination in poor condition. Care should be taken to protect the produce and it becomes necessary when mixing load of fruits and vegetables to prevent violating the compatibility factors.
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