The time necessary for crops to successfully complete reproduction is species and environment-dependent. Life cycles can be completed in a few weeks or take several years depending on the plant species.
Crop development is divided into phenophases that are affected primarily by light and temperature changes, interacting with phyto-hormones. Some species are influenced more by light and others by temperature.
Maturity/Quality Indices of Crop Products
Maturity at harvest is the most important determinant of storage life and final fruit quality. Immature fruit is highly susceptible to shriveling and mechanical damage and is of inferior flavor quality when ripe.
Overripe fruit is likely to become soft and mealy with an insipid flavor soon after harvest. Fruit picked either prematurely or too late, is more susceptible to post-harvest physiological disorders than fruit picked at the proper stage of maturity.
With a few exceptions, all fruits attain optimal eating quality when allowed to ripen on the plant. Some fruits are, however, picked at a mature but unripe stage of development so as to allow them to withstand post-harvest handling conditions when shipped over long distances.
Maturity indices for such fruit are based on a compromise between those indices that would ensure the best eating quality to the consumer and those that provide flexibility in marketing.
Fruit can be divided into two groups:
(1) Those that are incapable of continuing their ripening process once removed from the plant, and
(2) Those that can be harvested at the mature stage and allowed to ripen off the plant.
Group 1 includes cane berries, cherries, citrus fruits, grapes, lychee, pineapple, pomegranate, and strawberry.
Group 2 on the other hand, includes apple, apricot, avocado, banana, cherimoya, guava, kiwifruit, mango, nectarine, papaya, passion fruit, pear, peach, persimmon, plum, quince, and sapodilla
Fruit of the Group 1 category, produce very small quantities of ethylene and do not respond to ethylene treatment except in terms of de-greening (removal of chlorophyll); these should be picked when fully ripe if good flavor quality is to be ensured.
On the other hand, fruit of the Group 2 category produce comparably larger quantities of ethylene associated with their ripening and undergoes more rapid and uniform ripening upon exposure to ethylene.
Many vegetables, in particular leafy vegetables and immature fruit-vegetables (such as cucumbers, sweet corn, green beans, peas, and okra), attain optimum eating quality prior to reaching full maturity.
Maturity Indices
The maturity index of a fruit provides an indication of its stage of development or maturation.
Maturity indices are based on characteristics that are known to change as the fruit matures. Maturity indices for harvest can be either subjective or objective.
1. Physical Indices of Maturity
1. Skin color
This factor is commonly applied to fruits since skin colour changes as the fruit ripens or matures. Some fruits exhibit no perceptible colour change during maturation, depending on the type of fruit or vegetable.
Assessment of harvest maturity by skin colour depends on the judgment of the harvester, but colour charts are available for cultivars, such as apples, tomatoes, peaches, chili peppers, etc.
2. Optical Methods
Light transmission properties can be used to measure the degree of maturity of fruits. These methods are based on the chlorophyll content of the fruit, which is reduced during maturation.
The fruit is exposed to a bright light, which is then switched off so that the fruit is in total darkness. Next, a sensor measures the amount of light emitted from the fruit, which is proportional to its chlorophyll content and thus its maturity.
3. Shape
The shape of fruit can change during maturation and can be used as a characteristic to determine harvest maturity. For instance, a banana becomes more rounded in cross-sections and less angular as it develops on the plant.
Mangoes also change shape during maturation. As the mango matures on the tree the relationship between the shoulders of the fruit and the point at which the stalk is attached may change.
The shoulders of immature mangoes slope away from the fruit stalk; however, on more mature mangoes the shoulders become level with the point of attachment, and with even more maturity the shoulders may be raised above this point.
4. Size
Changes in the size of a crop while growing are frequently used to determine the time of harvest. For example, partially mature cobs of Zea mays saccharata are marketed as sweet corn, while even less mature and thus smaller cobs are marketed as baby corn.
For bananas, the width of individual fingers can be used to determine harvest maturity. Usually a finger is placed midway along the bunch and its maximum width is measured with caliper; this is referred to as the caliper grade.
5. Aroma
Most fruits synthesize volatile chemicals as they ripen. Such chemicals give fruit its characteristic odour and can be used to determine whether it is ripe or not. These doors may only be detectable by humans when a fruit is completely ripe, and therefore has limited use in commercial situations.
6. Fruit opening
Some fruits may develop toxic compounds during ripening, such as ackee tree fruit, which contains toxic levels of hypoglycine. The fruit splits when it is fully mature, revealing black seeds on yellow arils.
At this stage, it has been shown to contain minimal amounts of hypoglycine or none at all. This creates a problem in marketing; because the fruit is so mature, it will have a very short post-harvest life.
Analysis of hypoglycine A‘ (hyp) in ackee tree fruit revealed that the seed contained appreciable hyp at all stages of maturity, at approximately 1000 ppm, while levels in the membrane mirrored those in the arils.
This analysis supports earlier observations that unopened or partially opened ackee fruit should not be consumed, whereas fruit that opens naturally to over 15 mm of lobe separation poses little health hazard, provided the seed and membrane portions are removed.
7. Leaf changes
Leaf quality often determines when fruits and vegetables should be harvested. In root crops, the condition of the leaves can likewise indicate the condition of the crop below ground.
For example, if potatoes are to be stored, then the optimum harvest time is soon after the leaves and stems have died. If harvested earlier, the skins will be less resistant to harvesting and handling damage and more prone to storage diseases.
8. Abscission
As part of the natural development of a fruit an abscission layer is formed in the pedicel. For example, in cantaloupe melons, harvesting before the abscission layer is fully developed results in inferior flavoured fruit, compared to those left on the vine for the full period.
9. Firmness
A fruit may change in texture during maturation, especially during ripening when it may become rapidly softer. Excessive loss of moisture may also affect the texture of crops.
These textural changes are detected by touch, and the harvester may simply be able to gently squeeze the fruit and judge whether the crop can be harvested.
Today sophisticated devices have been developed to measure texture in fruits and vegetables, for example, texture analyzers and pressure testers; they are currently available for fruits and vegetables in various forms.
A force is applied to the surface of the fruit, allowing the probe of the penetrometer or tetrameter to penetrate the fruit flesh, which then gives a reading on firmness.
Hand-held pressure testers could give variable results because the basis on which they are used to measure firmness is affected by the angle at which the force is applied.
Two commonly used pressure testers to measure the firmness of fruits and vegetables are the Magness-Taylor and UC Fruit Firmness testers.
A more elaborate test, but not necessarily more effective, uses instruments like the Instron Universal Testing Machine. It is necessary to specify the instrument and all settings used when reporting test pressure values or attempting to set standards.
10. Juice content
The juice content of many fruits increases as the fruit matures on the tree. To measure the juice content of a fruit, a representative sample of fruit is taken and then the juice extracted in a standard and specified manner.
The juice volume is related to the original mass of juice, which is proportional to its maturity.
Read Also: Juvenility, Maturity and Senescence of Plants
2. Chemical Indices of Maturity
Sugars: In climacteric fruits, carbohydrates accumulate during maturation in the form of starch. As the fruit ripens, starch is broken down into sugar. In non-climacteric fruits, sugar tends to accumulate during maturation.
As the fruit ripens starch is broken down to sugars. Measurement of sugars indicate the stage of maturity or ripeness, sugar constitutes the major portion of soluble solid of fruit juice. Measurement of TSS is done on the refractometer
Starch: Starch content in developing fruit of pear and apple provides harvest maturity.
Acidity: In many fruits, the acidity changes during maturation and ripening, and in the case of citrus and other fruits, acidity reduces progressively as the fruit matures on the tree.
Quality Indices of Fruits
Quality i.e. the degree of excellence or superiority of fresh fruits and their products is combination of attributes, properties or characteristics that give each commodity value in terms of human food.
The relative importance of each quality component depends upon the commodity and its intended use (e.g., fresh or processed) and varies among producers, handlers and consumers.
To producers a given commodity must have high yield and good appearance, must be easy to harvest and must withstand long distance shipping to markets. Appearance quality, firmness, and shelf-life are important from the point of view of wholesale and retail marketers.
Consumers judge quality of fresh fruits on the basis of appearance including freshness and firmness at the time of initial purchases. Subsequent purchases depend upon the consumers satisfaction in terms of flavour (eating) quality of the product.
Consumers are also concerned about the nutritional quality of fresh fruits, which are only colourful and flavorful components of our diets, but also a good source of energy, vitamins, minerals, dietary fibers and many bioactive compounds that enhance human health
Maturity indices are important for deciding when a given commodity should be harvested to provide some marketing flexibility and ensure the attainment of acceptable eating quality to the consumer. These two goals are not always compatible.
The necessity of shipping fruits long distance has often resulted in harvesting them at less than ideal maturity. This in turn, has resulted in less than optimum quality to the consumer.
Most maturity indices are also factors of quality, but there are many important quality indices that are not used in determining the optimum harvesting stage.
Read Also: Understanding Maturity, Ripening, Senescence, and Types of Maturity
The flavor quality of fruits cannot be accurately determined by appearance factors alone. Also the post-harvest quality of fruits based on flavor is generally shorter than their postharvest-life based on appearance (such as color and absence of defects and decay).
1. Maturity Standards
Maturity standards have been determined for many fruit, vegetable and floral crops. Harvesting crops at the proper maturity allows handlers to begin their work with the best possible quality produce.
Produce harvested too early may lack flavor and may not ripen properly, while produce harvested too late may be fibrous or overripe. Pickers can be trained in methods of identifying produce that is ready for harvest.
The following table below provides some examples of maturity indices.
Table: Examples of Maturity indices of some fruits
| Index | Examples | |
| Elapsed days from full bloom to harvest | Apples, pears | |
| Mean heat units during development | Peas, apples, sweet corn | |
| Development of abscission layer | Some melons, apples | |
| Surface morphology and structure | Cuticle formation on grapes, tomatoes Netting of some melons . Gloss of some fruits (development of wax) | |
| Size | All fruits and many vegetables | |
| Specific gravity | Cherries, watermelons, potatoes | |
| Shape | Angularity of banana fingers Full cheeks of mangos Compactness of broccoli and cauliflower | |
| Solidity | Lettuce, cabbage, brussel sprouts | |
| Textural properties | ||
| Firmness | Apples, pears, stone fruits | |
| Tenderness | Peas | |
| Color, external | All fruits and most vegetables |
| Internal color and structure | Formation of jelly-like material in tomato fruits Flesh color of some fruits | |
| Compositional factors | ||
| Starch content | Apples, pears | |
| Sugar content | Apples, pears, stone fruits, grapes | |
| Acid content, sugar/acid ratio | Pomegranates, citrus, papaya, melons, kiwifruit | |
| Juice content | Citrus fruits | |
| Oil content | Avocados | |
| Astringency (tannin content) | Persimmons, dates | |
| Internal ethylene concentration | Apples, pears |
Vegetables are harvested over a wide range of maturities, depending upon the part of the plant used as food.
The table below provides some examples of maturity indices of vegetable crops.
Table: Examples of Maturity indices of vegetable crops
| Crop | Index | ||
| Root, bulb and tuber crops | |||
| Radish and carrot | Large enough and crispy | ||
| Potato, onion, and garlic | Tops beginning to dry out and topple down |
| Yam bean and ginger | Large enough (over-mature if tough and fibrous) | ||
| Green onion | Leaves at their broadest and longest | ||
| Fruit vegetables | |||
| Cowpea, snap bean, potato, sweet pea and winged bean | Well-filled pods that snap readily | ||
| Lima bean and pigeon pea | Well-filled pods that are beginning to lose their greenness | ||
| Okra | Desirable size reached and the tips of which can be snapped readily | ||
| Gourd | Desirable size reached and thumbnail can still penetrate flesh readily (over-mature if thumbnail cannot penetrate flesh readily) | ||
| Eggplant, bitter gourd, chayote or slicing cucumber | Desirable size reached but still tender (over- mature if color dulls or changes and seeds are tough) | ||
| Sweet corn | Exudes milky sap from kernel if cut | ||
| Tomato | Seeds slipping when fruit is cut, or green color turning pink | ||
| Sweet pepper | Deep green color turning dull or red | ||
| Muskmelon | Easily separated from vine with a slight twist leaving clean cavity | ||
| Honeydew melon | Change in fruit color from a slight greenish white to cream; aroma noticeable | ||
| Watermelon | Color of lower part turning creamy yellow, dull hollow sound when thumped | ||
| Flower vegetables | |||
| Cauliflower | Curd compact (over-mature if flower cluster elongates and become loose) | ||
| Broccoli | Bud cluster compact (over-mature if loose) | ||
| Leafy vegetables | |||
| Lettuce | Big enough before flowering |
| Cabbage | Head compact (over-mature if head cracks) | |
| Celery | Big enough before it becomes pithy |
In conclusion, maturity in virtually all crops can be divided into two types, physiological maturity which describes that period when sexually induced reproductive growth has ceased, and harvest maturity, where the seed, fruit, or another economically important organ of yield has reached a state of ripeness and can be removed from the parent plant for consumption.
Maturity at harvest is the most important determinant of storage-life and final fruit quality. Maturity indices are important for deciding when a given commodity should be harvested to provide some marketing flexibility and ensure the attainment of acceptable eating quality to the consumer.
The deteriorative processes which ultimately lead to complete loss of organization and functioning of the plant or its parts are known as senescence
Maturity indexes for most fruits and vegetables could be any or a combination of the following such as changes in colour, shape, size, aroma, fruit opening, abscission, leaf changes, firmness, juice content, sugar and acidity
The lifecycle duration of all agricultural crops is important to their management for maximum economic yield. For most agronomic crops maturity ratings refer to the time from germination until physiological maturity.
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