Maturity and Maturity indices
“Maturity is the attainment of a particular size or stage followed by ripening, called maturity.”
“It is also defined as the stage of development at which the product has completed its natural growth and is ready for harvesting.”
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This step will ensure the proper completion of the ripening process.
The word maturity is derived from the Latin word ‘maturus’ which means to ripen. This is the stage of fruit development that ensures maximum edible quality at the completion of the ripening process.
The principles that determine at what stage of maturity a fruit or vegetable should be harvested are critical to its subsequent storage and marketable life and quality. Fruits harvested too early may lack flavor and may not ripen properly after harvest; When the produce is harvested too late they will be fibrous or have a very limited market life.
Physiologists divide the life span of fruits and vegetables into three stages after harvesting: maturity, ripening, and senescence.
Maturation is a sign that the fruit is ready for harvesting. At this point, the edible portion of the fruit or vegetable is fully grown in size, although it may not be ready for immediate consumption.
Ripening follows or overlaps maturity, making the product edible, as indicated by the taste.
Senescence is the last stage in the ontogeny of the plant organ, Senescence is the final stage in the ontogeny of a plant organ, characterized by the natural degradation of a fruit or vegetable, as in loss of texture, taste, etc. (aging ends with the death of fruit tissue).
Maturity is divided into four categories.
This is the developmental stage of the fruit on the tree, which will result in a satisfactory product after harvesting.
It refers to the stage of development of fruits and vegetables when maximum growth and maturity have occurred. It is usually associated with full ripening in fruits. After physiological maturity comes senescence.
This is the state of essential plant organs for a market. It usually has little to do with physiological maturity and can occur at any stage during the developmental stage.
It can be defined in terms of physiological maturity and horticultural maturity, a stage that will allow the fruit/vegetable to reach its peak state when it reaches the consumer and develop an acceptable taste or appearance and has a sufficient shelf life.
Methods of Determination of Maturity
The maturity of the crop can be determined in different ways:
- Computation methods: (1) calendar date, (2) Days from Full bloom to Harvest, (3) Mean heat units.
- Physical Methods: (1) Fruit retention strength, (2) Fruit size and surface morphology (3) Weight, (4) Specific gravity, (5) Colour, (6) Flesh firmness, (7) T- Stage.
- Chemical Methods: (1) Titral Acidity (2) TSS/Acid Ratio, (3) Sugar-(Total and Reducing), (4) Sugar/Acid Ratio, (5) Bioelectrical Conductivity, (6) Starch-Iodine Test (7) Tannin content (8) Oil content, (8) Juice content, (9) Total Soluble Solids (TSS).
- Physiological Methods: (1) Respiration Rate and (2) Ethylene evolution Rate
Determination of maturity
No one method of maturity indices is satisfactory, a combination of the following may be better than relying on one.
- Peel colour: The change in color of many fruits is a valuable guide to maturity. Initially, the dark green color gradually decreases in intensity and the color becomes lighter in many fruits. The green disappears completely with the development of yellow, red, or purple pigments. Some fruits do not show any visible colour change during maturity. Assessing crop maturity by skin color depends on the decision of the grower, but colour charts are available for varieties in apple, tomato, peach, chilli, capsicum, etc. Although the human eye is used to evaluate colour outcomes, it can be quite different from human differences in color perception. Therefore, a special device is used to assign a specific color value based on the amount of light reflected from the surface of the object or the light transmitted through the object. This instrument can measure small differences in color accuracy and can be used automatically in the packing line. This instrument is popularly known as colour difference meter. This instrument uses the colorimetric method for colour measurement. This method is not completely reliable as it is affected by factors other than maturity.
- Shape: The shape of the fruit changes during maturity and can be used as a feature to determine the maturity of the crop. For example, a banana becomes more rounded in cross-section and less angular as it develops on the plant. Mangoes also change shape during maturity. As the mango matures on the tree, the relationship between the shoulders of the fruit and the point at which it attaches to the stalk may change. The shoulders of immature mangoes are bent away from the fruit stalk; However, on more mature mangoes the shoulders become flat with the point of attachment, and on even more mature mangoes the shoulders may rise above this point.
Size: Variation in fruit/vegetable size is often used to determine the maturity time of harvesting. Size is generally of limited importance as a maturity index in fruits, although it is widely used for vegetables, especially those marketed at the time of their development. For products, size is often specified as a quality standard, with a larger size generally indicating a commercially mature product and a smaller size indicating an immature product. However, this assumption is not always a reliable guide for all purposes.
Optical methods: The 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 decreases during maturity. The fruit is exposed to a bright light, which is then turned off so that the fruit is completely dark. Next, a sensor measures the amount of light emitted from the fruit, which is proportional to its chlorophyll content and thus its ripeness.
Heat units/degree days: It is the value of time required for the maturity of fruit after flowering by measuring degree days or heat units in a particular environment. It has been found that a crop usually requires a specific number of heat units or degree days to mature under warm conditions, and maturity will be quicker and maturity will be delayed in colder conditions. The number of degree days to maturity is determined over a period of several years by obtaining an algebraic sum, plus or minus the difference between the daily average temperature and a fixed base temperature (usually the minimum temperature at which growth occurs). The average or the specific number of degree days is used to forecast the likely date of maturity for the current year.
Aroma: Most fruits synthesize volatile chemicals during ripening. Such chemicals give the fruit its distinctive odor and can be used to determine whether it is ripe. These odors can only be detected by humans when the fruit is fully ripe, and therefore have limited use in commercial situations.
Leaf changes: The quality of foliage often determines when fruits and vegetables should be harvested. In root crops, the position of the leaves can also indicate the position of the crop below the ground. For example, if potatoes are to be stored, the appropriate time to harvest is immediately after the leaves and stems die off. If dug earlier, the peel will be less resistant to harvesting and handling damage and more prone to storage diseases. Apple leaves turn green to light green and yellow at maturity.
Abscission: As a stage of the natural development of the fruit, an abscission layer is formed in the pedicel. For example, in melons, the fruit does not taste as good when harvested before the abscission layer, as compared to fruits left on the vine for the entire period.
Firmness: The fruit changes in texture during maturity, especially during ripening when it can become increasingly soft. Excessive loss of moisture can also affect the texture of crops. These texture changes are detected by touch, and the grower may be able to determine by simply pressing the fruit gently. Nowadays, sophisticated instruments have been developed to measure texture in fruits and vegetables, for example, texture analyzers and pressure testers; They are currently available in various forms for fruits and vegetables. A force is applied to the surface of the fruit, allowing the probe of the penetrometer or texturometer to penetrate the flesh (pulp) of the fruit, which then gives a reading on their firmness. Two commonly used pressure testers to measure the firmness of fruits and vegetables are the Magness-Taylor and the UC Fruit Firmness Tester.
Quantity of juice: As the fruits ripen on the tree, the amount of juice increases in many fruits. To measure the amount of fruit juice, a representative sample of the fruit is taken, and then the juice is extracted in a standard and specified manner. The amount of juice is related to the original mass of the juice, which is proportional to its maturity. The minimum values for citrus juices are presented in the table.
Minimum juice values for mature citrus
Oil content and dry matter percentage: Oil content can be used to determine the ripeness of fruit, such as an avocado. According to the California Agricultural Code, at the time of harvest and at any time thereafter, avocados must contain not less than 8% oil per avocado, excluding the skin and seeds, similarly, the oil content of an avocado is related to the moisture content. The oil content is determined by weighing 5–10 g of avocado pulp and then extracting the oil with a solvent (eg, benzene or petroleum ether) in a distillation column. This method has been successful for those crops which have naturally high oil content.
Moisture content: During the development of avocado fruit, the oil content increases, and the moisture content decreases rapidly. The required moisture levels for different types of avocados grown in Chile are listed in the table below.
Sugars: In seasonal fruits, carbohydrates are stored as starch during maturity. As fruits ripen, starch breaks down into sugars. In off-season fruits, sugars are stored during maturity. A quick way to measure the amount of sugar in fruits is with a refractometer. A drop of fruit juice is placed in the sample holder of the refractometer and a reading is taken; It is equal to the total amount of soluble solids or sugars. This factor is used to specify maturity in many parts of the world.
Starch content: Measurement of starch content is a reliable technique for determining ripeness in pear and apple varieties. The method involves cutting the fruit into two halves and dipping the cut pieces in a solution containing 4% potassium iodide or 1% iodine. The cut surface turns a bluish-black color in places where starch is present. As harvest time approaches, starch turns into sugar. Harvesting begins when samples show that 65-70% of the cut surface has turned blue-black.
Acidity: In many fruits, acidity changes during maturity and ripening, and in citrus and other fruits, the acidity progressively decreases as the fruit matures on the tree. Taking samples of such fruits, extracting the juice, and titrating it with a standard alkaline solution, is one measure that can be related to the optimum time of harvest. Generally, acidity is not taken as a measure of fruit maturity, but in relation to the soluble solids, called the Brix: acid ratio.
Specific Gravity: Specific gravity is the relative gravity, or the weight of a solid or liquid, compared to pure distilled water at 62 °F (16.7 °C), which is considered to be unity. Specific gravity is obtained by comparing the weight of the equivalent bulk of other bodies with the weight of the water. In practice, the fruit or vegetable is weighed in air, then in purified water. The weight in air divided by the weight in water gives the specific gravity. This will ensure a reliable measure of fruit maturity. As the fruit matures, its specific gravity increases. This parameter is rarely used to determine harvest time. However, it is used after harvest to grade crops according to different maturities. This is done by placing the fruit in a water tank, in which the swimmers are less mature than the sinkers.
Maturity index of some fruits and vegetables